Contents
- Abstract
- SIL in the Swift Compiler
- Syntax
- Dataflow Errors
- Runtime Failure
- Undefined Behavior
- Calling Convention
- Type Based Alias Analysis
- Value Dependence
- Instruction Set
- Allocation and Deallocation
- Debug Information
- Accessing Memory
- Reference Counting
- strong_retain
- strong_release
- set_deallocating
- strong_retain_unowned
- unowned_retain
- unowned_release
- load_weak
- store_weak
- load_unowned
- store_unowned
- fix_lifetime
- mark_dependence
- is_unique
- is_escaping_closure
- copy_block
- copy_block_without_escaping
- builtin "unsafeGuaranteed"
- builtin "unsafeGuaranteedEnd"
- Literals
- Dynamic Dispatch
- Function Application
- Metatypes
- Aggregate Types
- retain_value
- retain_value_addr
- unmanaged_retain_value
- copy_value
- release_value
- release_value_addr
- unmanaged_release_value
- destroy_value
- autorelease_value
- tuple
- tuple_extract
- tuple_element_addr
- destructure_tuple
- struct
- struct_extract
- struct_element_addr
- destructure_struct
- object
- ref_element_addr
- ref_tail_addr
- Enums
- Protocol and Protocol Composition Types
- init_existential_addr
- init_existential_value
- deinit_existential_addr
- deinit_existential_value
- open_existential_addr
- open_existential_value
- init_existential_ref
- open_existential_ref
- init_existential_metatype
- open_existential_metatype
- alloc_existential_box
- project_existential_box
- open_existential_box
- open_existential_box_value
- dealloc_existential_box
- Blocks
- Unchecked Conversions
- upcast
- address_to_pointer
- pointer_to_address
- unchecked_ref_cast
- unchecked_ref_cast_addr
- unchecked_addr_cast
- unchecked_trivial_bit_cast
- unchecked_bitwise_cast
- ref_to_raw_pointer
- raw_pointer_to_ref
- ref_to_unowned
- unowned_to_ref
- ref_to_unmanaged
- unmanaged_to_ref
- convert_function
- convert_escape_to_noescape
- thin_function_to_pointer
- pointer_to_thin_function
- classify_bridge_object
- value_to_bridge_object
- ref_to_bridge_object
- bridge_object_to_ref
- bridge_object_to_word
- thin_to_thick_function
- thick_to_objc_metatype
- objc_to_thick_metatype
- objc_metatype_to_object
- objc_existential_metatype_to_object
- Checked Conversions
- Runtime Failures
- Terminators
- Assertion configuration
SIL is an SSA-form IR with high-level semantic information designed to implement the Swift programming language. SIL accommodates the following use cases:
- A set of guaranteed high-level optimizations that provide a predictable baseline for runtime and diagnostic behavior.
- Diagnostic dataflow analysis passes that enforce Swift language requirements, such as definitive initialization of variables and constructors, code reachability, switch coverage.
- High-level optimization passes, including retain/release optimization, dynamic method devirtualization, closure inlining, memory allocation promotion, and generic function instantiation.
- A stable distribution format that can be used to distribute "fragile" inlineable or generic code with Swift library modules, to be optimized into client binaries.
In contrast to LLVM IR, SIL is a generally target-independent format representation that can be used for code distribution, but it can also express target-specific concepts as well as LLVM can.
For more information on developing the implementation of SIL and SIL passes, see SILProgrammersManual.md.
At a high level, the Swift compiler follows a strict pipeline architecture:
- The Parse module constructs an AST from Swift source code.
- The Sema module type-checks the AST and annotates it with type information.
- The SILGen module generates raw SIL from an AST.
- A series of Guaranteed Optimization Passes and Diagnostic Passes are run over the raw SIL both to perform optimizations and to emit language-specific diagnostics. These are always run, even at -Onone, and produce canonical SIL.
- General SIL Optimization Passes optionally run over the canonical SIL to improve performance of the resulting executable. These are enabled and controlled by the optimization level and are not run at -Onone.
- IRGen lowers canonical SIL to LLVM IR.
- The LLVM backend (optionally) applies LLVM optimizations, runs the LLVM code generator and emits binary code.
The stages pertaining to SIL processing in particular are as follows:
SILGen produces raw SIL by walking a type-checked Swift AST. The form of SIL emitted by SILGen has the following properties:
- Variables are represented by loading and storing mutable memory locations
instead of being in strict SSA form. This is similar to the initial
alloca
-heavy LLVM IR emitted by frontends such as Clang. However, Swift represents variables as reference-counted "boxes" in the most general case, which can be retained, released, and captured into closures. - Dataflow requirements, such as definitive assignment, function returns, switch coverage (TBD), etc. have not yet been enforced.
transparent
function optimization has not yet been honored.
These properties are addressed by subsequent guaranteed optimization and diagnostic passes which are always run against the raw SIL.
After SILGen, a deterministic sequence of optimization passes is run over the raw SIL. We do not want the diagnostics produced by the compiler to change as the compiler evolves, so these passes are intended to be simple and predictable.
- Mandatory inlining inlines calls to "transparent" functions.
- Memory promotion is implemented as two optimization phases, the first
of which performs capture analysis to promote
alloc_box
instructions toalloc_stack
, and the second of which promotes non-address-exposedalloc_stack
instructions to SSA registers. - Constant propagation folds constant expressions and propagates the constant values. If an arithmetic overflow occurs during the constant expression computation, a diagnostic is issued.
- Return analysis verifies that each function returns a value on every
code path and doesn't "fall off the end" of its definition, which is an error.
It also issues an error when a
noreturn
function returns. - Critical edge splitting splits all critical edges from terminators that don't support arbitrary basic block arguments (all non cond_branch terminators).
If all diagnostic passes succeed, the final result is the canonical SIL for the program.
TODO:
- Generic specialization
- Basic ARC optimization for acceptable performance at -Onone.
SIL captures language-specific type information, making it possible to perform high-level optimizations that are difficult to perform on LLVM IR.
- Generic Specialization analyzes specialized calls to generic functions and generates new specialized version of the functions. Then it rewrites all specialized usages of the generic to a direct call of the appropriate specialized function.
- Witness and VTable Devirtualization for a given type looks up the associated method from a class's vtable or a type witness table and replaces the indirect virtual call with a call to the mapped function.
- Performance Inlining
- Reference Counting Optimizations
- Memory Promotion/Optimizations
- High-level domain specific optimizations The Swift compiler implements high-level optimizations on basic Swift containers such as Array or String. Domain specific optimizations require a defined interface between the standard library and the optimizer. More details can be found here: HighLevelSILOptimizations
SIL is reliant on Swift's type system and declarations, so SIL syntax
is an extension of Swift's. A .sil
file is a Swift source file
with added SIL definitions. The Swift source is parsed only for its
declarations; Swift func
bodies (except for nested declarations)
and top-level code are ignored by the SIL parser. In a .sil
file,
there are no implicit imports; the swift
and/or Builtin
standard modules must be imported explicitly if used.
Here is an example of a .sil
file:
sil_stage canonical
import Swift
// Define types used by the SIL function.
struct Point {
var x : Double
var y : Double
}
class Button {
func onClick()
func onMouseDown()
func onMouseUp()
}
// Declare a Swift function. The body is ignored by SIL.
func taxicabNorm(_ a:Point) -> Double {
return a.x + a.y
}
// Define a SIL function.
// The name @_T5norms11taxicabNormfT1aV5norms5Point_Sd is the mangled name
// of the taxicabNorm Swift function.
sil @_T5norms11taxicabNormfT1aV5norms5Point_Sd : $(Point) -> Double {
bb0(%0 : $Point):
// func Swift.+(Double, Double) -> Double
%1 = function_ref @_Tsoi1pfTSdSd_Sd
%2 = struct_extract %0 : $Point, #Point.x
%3 = struct_extract %0 : $Point, #Point.y
%4 = apply %1(%2, %3) : $(Double, Double) -> Double
return %4 : Double
}
// Define a SIL vtable. This matches dynamically-dispatched method
// identifiers to their implementations for a known static class type.
sil_vtable Button {
#Button.onClick!1: @_TC5norms6Button7onClickfS0_FT_T_
#Button.onMouseDown!1: @_TC5norms6Button11onMouseDownfS0_FT_T_
#Button.onMouseUp!1: @_TC5norms6Button9onMouseUpfS0_FT_T_
}
decl ::= sil-stage-decl
sil-stage-decl ::= 'sil_stage' sil-stage
sil-stage ::= 'raw'
sil-stage ::= 'canonical'
There are different invariants on SIL depending on what stage of processing has been applied to it.
- Raw SIL is the form produced by SILGen that has not been run through
guaranteed optimizations or diagnostic passes. Raw SIL may not have a
fully-constructed SSA graph. It may contain dataflow errors. Some instructions
may be represented in non-canonical forms, such as
assign
anddestroy_addr
for non-address-only values. Raw SIL should not be used for native code generation or distribution. - Canonical SIL is SIL as it exists after guaranteed optimizations and diagnostics. Dataflow errors must be eliminated, and certain instructions must be canonicalized to simpler forms. Performance optimization and native code generation are derived from this form, and a module can be distributed containing SIL in this (or later) forms.
SIL files declare the processing stage of the included SIL with one of the
declarations sil_stage raw
or sil_stage canonical
at top level. Only
one such declaration may appear in a file.
sil-type ::= '$' '*'? generic-parameter-list? type
SIL types are introduced with the $
sigil. SIL's type system is
closely related to Swift's, and so the type after the $
is parsed
largely according to Swift's type grammar.
A formal type is the type of a value in Swift, such as an expression result. Swift's formal type system intentionally abstracts over a large number of representational issues like ownership transfer conventions and directness of arguments. However, SIL aims to represent most such implementation details, and so these differences deserve to be reflected in the SIL type system. Type lowering is the process of turning a formal type into its lowered type.
It is important to be aware that the lowered type of a declaration need not be the lowered type of the formal type of that declaration. For example, the lowered type of a declaration reference:
- will usually be thin,
- will frequently be uncurried,
- may have a non-Swift calling convention,
- may use bridged types in its interface, and
- may use ownership conventions that differ from Swift's default conventions.
Generic functions working with values of unconstrained type must generally work with them indirectly, e.g. by allocating sufficient memory for them and then passing around pointers to that memory. Consider a generic function like this:
func generateArray<T>(n : Int, generator : () -> T) -> [T]
The function generator
will be expected to store its result
indirectly into an address passed in an implicit parameter. There's
really just no reasonable alternative when working with a value of
arbitrary type:
- We don't want to generate a different copy of
generateArray
for every typeT
. - We don't want to give every type in the language a common representation.
- We don't want to dynamically construct a call to
generator
depending on the typeT
.
But we also don't want the existence of the generic system to force
inefficiencies on non-generic code. For example, we'd like a function
of type () -> Int
to be able to return its result directly; and
yet, () -> Int
is a valid substitution of () -> T
, and a
caller of generateArray<Int>
should be able to pass an arbitrary
() -> Int
in as the generator.
Therefore, the representation of a formal type in a generic context may differ from the representation of a substitution of that formal type. We call such differences abstraction differences.
SIL's type system is designed to make abstraction differences always result in differences between SIL types. The goal is that a properly- abstracted value should be correctly usable at any level of substitution.
In order to achieve this, the formal type of a generic entity should always be lowered using the abstraction pattern of its unsubstituted formal type. For example, consider the following generic type:
struct Generator<T> {
var fn : () -> T
}
var intGen : Generator<Int>
intGen.fn
has the substituted formal type () -> Int
, which
would normally lower to the type @callee_owned () -> Int
, i.e.
returning its result directly. But if that type is properly lowered
with the pattern of its unsubstituted type () -> T
, it becomes
@callee_owned () -> @out Int
.
When a type is lowered using the abstraction pattern of an unrestricted type, it is lowered as if the pattern were replaced with a type sharing the same structure but replacing all materializable types with fresh type variables.
For example, if g
has type Generator<(Int, Int) -> Float>
, g.fn
is
lowered using the pattern () -> T
, which eventually causes (Int, Int)
-> Float
to be lowered using the pattern T
, which is the same as
lowering it with the pattern U -> V
; the result is that g.fn
has the following lowered type:
@callee_owned () -> @owned @callee_owned (@in (Int, Int)) -> @out Float.
As another example, suppose that h
has type
Generator<(Int, inout Int) -> Float>
. Neither (Int, inout Int)
nor inout Int
are potential results of substitution because they
aren't materializable, so h.fn
has the following lowered type:
@callee_owned () -> @owned @callee_owned (@in Int, @inout Int) -> @out Float
This system has the property that abstraction patterns are preserved
through repeated substitutions. That is, you can consider a lowered
type to encode an abstraction pattern; lowering T
by R
is
equivalent to lowering T
by (S
lowered by R
).
SILGen has procedures for converting values between abstraction patterns.
At present, only function and tuple types are changed by abstraction differences.
The type of a value in SIL shall be:
- a loadable legal SIL type,
$T
, - the address of a legal SIL type,
$*T
, or
A type T
is a legal SIL type if:
- it is a function type which satisfies the constraints (below) on function types in SIL,
- it is a metatype type which describes its representation,
- it is a tuple type whose element types are legal SIL types,
- it is
Optional<U>
, whereU
is a legal SIL type, - it is a legal Swift type that is not a function, tuple, optional, metatype, or l-value type, or
- it is a
@box
containing a legal SIL type.
Note that types in other recursive positions in the type grammar are still formal types. For example, the instance type of a metatype or the type arguments of a generic type are still formal Swift types, not lowered SIL types.
The address of T $*T
is a pointer to memory containing a value
of any reference or value type $T
. This can be an internal
pointer into a data structure. Addresses of loadable types can be
loaded and stored to access values of those types.
Addresses of address-only types (see below) can only be used with
instructions that manipulate their operands indirectly by address, such
as copy_addr
or destroy_addr
, or as arguments to functions.
It is illegal to have a value of type $T
if T
is address-only.
Addresses are not reference-counted pointers like class values are. They cannot be retained or released.
Address types are not first-class: they cannot appear in recursive
positions in type expressions. For example, the type $**T
is not
a legal type.
The address of an address cannot be directly taken. $**T
is not a representable
type. Values of address type thus cannot be allocated, loaded, or stored
(though addresses can of course be loaded from and stored to).
Addresses can be passed as arguments to functions if the corresponding parameter is indirect. They cannot be returned.
Captured local variables and the payloads of indirect
value types are stored
on the heap. The type @box T
is a reference-counted type that references
a box containing a mutable value of type T
. Boxes always use Swift-native
reference counting, so they can be queried for uniqueness and cast to the
Builtin.NativeObject
type.
A concrete or existential metatype in SIL must describe its representation. This can be:
@thin
, meaning that it requires no storage and thus necessarily represents an exact type (only allowed for concrete metatypes);@thick
, meaning that it stores a reference to a type or (if a concrete class) a subclass of that type; or@objc
, meaning that it stores a reference to a class type (or a subclass thereof) using an Objective-C class object representation rather than the native Swift type-object representation.
Function types in SIL are different from function types in Swift in a number of ways:
A SIL function type may be generic. For example, accessing a generic function with
function_ref
will give a value of generic function type.A SIL function type may be declared
@noescape
. This is required for any function type passed to a parameter not declared with@escaping
declaration modifier.@noescape
function types may be either@convention(thin)
or@callee_guaranteed
. They have an unowned context--the context's lifetime must be independently guaranteed.A SIL function type declares its conventional treatment of its context value:
- If it is
@convention(thin)
, the function requires no context value. Such types may also be declared@noescape
, which trivially has no effect passing the context value. - If it is
@callee_guaranteed
, the context value is treated as a direct parameter. This implies@convention(thick)
. If the function type is also@noescape
, then the context value is unowned, otherwise it is guaranteed. - If it is
@callee_owned
, the context value is treated as an owned direct parameter. This implies@convention(thick)
and is mutually exclusive with@noescape
. - If it is
@convention(block)
, the context value is treated as an unowned direct parameter. - Other function type conventions are described in
Properties of Types
andCalling Convention
.
- If it is
A SIL function type declares the conventions for its parameters. The parameters are written as an unlabeled tuple; the elements of that tuple must be legal SIL types, optionally decorated with one of the following convention attributes.
The value of an indirect parameter has type
*T
; the value of a direct parameter has typeT
.- An
@in
parameter is indirect. The address must be of an initialized object; the function is responsible for destroying the value held there. - An
@inout
parameter is indirect. The address must be of an initialized object. The memory must remain initialized for the duration of the call until the function returns. The function may mutate the pointee, and furthermore may weakly assume that there are no aliasing reads from or writes to the argument, though must preserve a valid value at the argument so that well-ordered aliasing violations do not compromise memory safety. This allows for optimizations such as local load and store propagation, introduction or elimination of temporary copies, and promotion of the@inout
parameter to an@owned
direct parameter and result pair, but does not admit "take" optimization out of the parameter or other optimization that would leave memory in an uninitialized state. - An
@inout_aliasable
parameter is indirect. The address must be of an initialized object. The memory must remain initialized for the duration of the call until the function returns. The function may mutate the pointee, and must assume that other aliases may mutate it as well. These aliases however can be assumed to be well-typed and well-ordered; ill-typed accesses and data races to the parameter are still undefined. - An
@owned
parameter is an owned direct parameter. - A
@guaranteed
parameter is a guaranteed direct parameter. - An
@in_guaranteed
parameter is indirect. The address must be of an initialized object; both the caller and callee promise not to mutate the pointee, allowing the callee to read it. - An
@in_constant
parameter is indirect. The address must be of an initialized object; the function will treat the value held there as read-only. - Otherwise, the parameter is an unowned direct parameter.
- An
A SIL function type declares the conventions for its results. The results are written as an unlabeled tuple; the elements of that tuple must be legal SIL types, optionally decorated with one of the following convention attributes. Indirect and direct results may be interleaved.
Indirect results correspond to implicit arguments of type
*T
in function entry blocks and in the arguments toapply
andtry_apply
instructions. These arguments appear in the order in which they appear in the result list, always before any parameters.Direct results correspond to direct return values of type
T
. A SIL function type has areturn type
derived from its direct results in the following way: when there is a single direct result, the return type is the type of that result; otherwise, it is the tuple type of the types of all the direct results, in the order they appear in the results list. The return type is the type of the operand ofreturn
instructions, the type ofapply
instructions, and the type of the normal result oftry_apply
instructions.- An
@out
result is indirect. The address must be of an uninitialized object. The function is required to leave an initialized value there unless it terminates with athrow
instruction or it has a non-Swift calling convention. - An
@owned
result is an owned direct result. - An
@autoreleased
result is an autoreleased direct result. If there is an autoreleased result, it must be the only direct result. - Otherwise, the parameter is an unowned direct result.
- An
A direct parameter or result of trivial type must always be unowned.
An owned direct parameter or result is transferred to the recipient, which becomes responsible for destroying the value. This means that the value is passed at +1.
An unowned direct parameter or result is instantaneously valid at the
point of transfer. The recipient does not need to worry about race
conditions immediately destroying the value, but should copy it
(e.g. by strong_retain
ing an object pointer) if the value will be
needed sooner rather than later.
A guaranteed direct parameter is like an unowned direct parameter
value, except that it is guaranteed by the caller to remain valid
throughout the execution of the call. This means that any
strong_retain
, strong_release
pairs in the callee on the
argument can be eliminated.
An autoreleased direct result must have a type with a retainable
pointer representation. Autoreleased results are nominally transferred
at +0, but the runtime takes steps to ensure that a +1 can be safely
transferred, and those steps require precise code-layout control.
Accordingly, the SIL pattern for an autoreleased convention looks exactly
like the SIL pattern for an owned convention, and the extra runtime
instrumentation is inserted on both sides when the SIL is lowered into
LLVM IR. An autoreleased apply
of a function that is defined with
an autoreleased result has the effect of a +1 transfer of the result.
An autoreleased apply
of a function that is not defined with
an autoreleased result has the effect of performing a strong retain in
the caller. A non-autoreleased apply
of a function that is defined
with an autoreleased result has the effect of performing an
autorelease in the callee.
SIL function types may provide an optional error result, written by placing
@error
on a result. An error result is always implicitly@owned
. Only functions with a native calling convention may have an error result.A function with an error result cannot be called with
apply
. It must be called withtry_apply
. There is one exception to this rule: a function with an error result can be called withapply [nothrow]
if the compiler can prove that the function does not actually throw.return
produces a normal result of the function. To return an error result, usethrow
.Type lowering lowers the
throws
annotation on formal function types into more concrete error propagation:- For native Swift functions,
throws
is turned into an error result. - For non-native Swift functions,
throws
is turned in an explicit error-handling mechanism based on the imported API. The importer only imports non-native methods and types asthrows
when it is possible to do this automatically.
- For native Swift functions,
A coroutine is a function which can suspend itself and return control to its caller without terminating the function. That is, it does not need to obey a strict stack discipline.
SIL supports two kinds of coroutine: @yield_many
and @yield_once
.
Either of these attributes may be written before a function type to
indicate that it is a coroutine type.
A coroutine type may declare any number of yielded values, which is to
say, values which are provided to the caller at a yield point. Yielded
values are written in the result list of a function type, prefixed by
the @yields
attribute. A yielded value may have a convention attribute,
taken from the set of parameter attributes and interpreted as if the yield
site were calling back to the calling function.
Currently, a coroutine may not have normal results.
Coroutine functions may be used in many of the same ways as normal
function values. However, they cannot be called with the standard
apply
or try_apply
instructions. A non-throwing yield-once
coroutine can be called with the begin_apply
instruction. There
is no support yet for calling a throwing yield-once coroutine or for
calling a yield-many coroutine of any kind.
Coroutines may contain the special yield
and unwind
instructions.
A @yield_many
coroutine may yield as many times as it desires.
A @yield_once
coroutine may yield exactly once before returning,
although it may also throw
before reaching that point.
This coroutine representation is well-suited to coroutines whose control
flow is tightly integrated with their callers and which intend to pass
information back and forth. This matches the needs of generalized
accessor and generator features in Swift. It is not a particularly good
match for async
/await
-style features; a simpler representation
would probably do fine for that.
SIL classifies types into additional subgroups based on ABI stability and generic constraints:
Loadable types are types with a fully exposed concrete representation:
- Reference types
- Builtin value types
- Fragile struct types in which all element types are loadable
- Tuple types in which all element types are loadable
- Class protocol types
- Archetypes constrained by a class protocol
A loadable aggregate type is a tuple or struct type that is loadable.
A trivial type is a loadable type with trivial value semantics. Values of trivial type can be loaded and stored without any retain or release operations and do not need to be destroyed.
Runtime-sized types are restricted value types for which the compiler does not know the size of the type statically:
- Resilient value types
- Fragile struct or tuple types that contain resilient types as elements at any depth
- Archetypes not constrained by a class protocol
Address-only types are restricted value types which cannot be loaded or otherwise worked with as SSA values:
- Runtime-sized types
- Non-class protocol types
- @weak types
Values of address-only type ("address-only values") must reside in memory and can only be referenced in SIL by address. Addresses of address-only values cannot be loaded from or stored to. SIL provides special instructions for indirectly manipulating address-only values, such as
copy_addr
anddestroy_addr
.
Some additional meaningful categories of type:
- A heap object reference type is a type whose representation consists of a
single strong-reference-counted pointer. This includes all class types,
the
Builtin.NativeObject
andAnyObject
types, and archetypes that conform to one or more class protocols. - A reference type is more general in that its low-level representation may
include additional global pointers alongside a strong-reference-counted
pointer. This includes all heap object reference types and adds
thick function types and protocol/protocol composition types that conform to
one or more class protocols. All reference types can be
retain
-ed andrelease
-d. Reference types also have ownership semantics for their referenced heap object; see Reference Counting below. - A type with retainable pointer representation is guaranteed to
be compatible (in the C sense) with the Objective-C
id
type. The value at runtime may benil
. This includes classes, class metatypes, block functions, and class-bounded existentials with only Objective-C-compatible protocol constraints, as well as one level ofOptional
orImplicitlyUnwrappedOptional
applied to any of the above. Types with retainable pointer representation can be returned via the@autoreleased
return convention.
SILGen does not always map Swift function types one-to-one to SIL function types. Function types are transformed in order to encode additional attributes:
The convention of the function, indicated by the
@convention(convention)
attribute. This is similar to the language-level
@convention
attribute, though SIL extends the set of supported conventions with additional distinctions not exposed at the language level:@convention(thin)
indicates a "thin" function reference, which uses the Swift calling convention with no special "self" or "context" parameters.@convention(thick)
indicates a "thick" function reference, which uses the Swift calling convention and carries a reference-counted context object used to represent captures or other state required by the function. This attribute is implied by@callee_owned
or@callee_guaranteed
.@convention(block)
indicates an Objective-C compatible block reference. The function value is represented as a reference to the block object, which is anid
-compatible Objective-C object that embeds its invocation function within the object. The invocation function uses the C calling convention.@convention(c)
indicates a C function reference. The function value carries no context and uses the C calling convention.@convention(objc_method)
indicates an Objective-C method implementation. The function uses the C calling convention, with the SIL-levelself
parameter (by SIL convention mapped to the final formal parameter) mapped to theself
and_cmd
arguments of the implementation.@convention(method)
indicates a Swift instance method implementation. The function uses the Swift calling convention, using the specialself
parameter.@convention(witness_method)
indicates a Swift protocol method implementation. The function's polymorphic convention is emitted in such a way as to guarantee that it is polymorphic across all possible implementors of the protocol.
The fully uncurried representation of the function type, with all of the curried argument clauses flattened into a single argument clause. For instance, a curried function
func foo(_ x:A)(y:B) -> C
might be emitted as a function of type((y:B), (x:A)) -> C
. The exact representation depends on the function's calling convention, which determines the exact ordering of currying clauses. Methods are treated as a form of curried function.
(This section applies only to Swift 1.0 and will hopefully be obviated in future releases.)
SIL tries to be ignorant of the details of type layout, and low-level
bit-banging operations such as pointer casts are generally undefined. However,
as a concession to implementation convenience, some types are allowed to be
considered layout compatible. Type T
is layout compatible with type
U
iff:
- an address of type
$*U
can be cast byaddress_to_pointer
/pointer_to_address
to$*T
and a valid value of typeT
can be loaded out (or indirectly used, ifT
is address- only), - if
T
is a nontrivial type, thenretain_value
/release_value
of the loadedT
value is equivalent toretain_value
/release_value
of the originalU
value.
This is not always a commutative relationship; T
can be layout-compatible
with U
whereas U
is not layout-compatible with T
. If the layout
compatible relationship does extend both ways, T
and U
are
commutatively layout compatible. It is however always transitive; if T
is layout-compatible with U
and U
is layout-compatible with V
, then
T
is layout-compatible with V
. All types are layout-compatible with
themselves.
The following types are considered layout-compatible:
Builtin.RawPointer
is commutatively layout compatible with all heap object reference types, andOptional
of heap object reference types. (Note thatRawPointer
is a trivial type, so does not have ownership semantics.)Builtin.RawPointer
is commutatively layout compatible withBuiltin.Word
.- Structs containing a single stored property are commutatively layout compatible with the type of that property.
- A heap object reference is commutatively layout compatible with any type
that can correctly reference the heap object. For instance, given a class
B
and a derived classD
inheriting fromB
, a value of typeB
referencing an instance of typeD
is layout compatible with bothB
andD
, as well asBuiltin.NativeObject
andAnyObject
. It is not layout compatible with an unrelated class typeE
. - For payloaded enums, the payload type of the first payloaded case is layout-compatible with the enum (not commutatively).
sil-identifier ::= [A-Za-z_0-9]+
sil-value-name ::= '%' sil-identifier
sil-value ::= sil-value-name
sil-value ::= 'undef'
sil-operand ::= sil-value ':' sil-type
SIL values are introduced with the %
sigil and named by an
alphanumeric identifier, which references the instruction or basic block
argument that produces the value. SIL values may also refer to the keyword
'undef', which is a value of undefined contents.
Unlike LLVM IR, SIL instructions that take value operands only accept
value operands. References to literal constants, functions, global variables, or
other entities require specialized instructions such as integer_literal
,
function_ref
, global_addr
, etc.
decl ::= sil-function
sil-function ::= 'sil' sil-linkage? sil-function-name ':' sil-type
'{' sil-basic-block+ '}'
sil-function-name ::= '@' [A-Za-z_0-9]+
SIL functions are defined with the sil
keyword. SIL function names
are introduced with the @
sigil and named by an alphanumeric
identifier. This name will become the LLVM IR name for the function,
and is usually the mangled name of the originating Swift declaration.
The sil
syntax declares the function's name and SIL type, and
defines the body of the function inside braces. The declared type must
be a function type, which may be generic.
sil-basic-block ::= sil-label sil-instruction-def* sil-terminator
sil-label ::= sil-identifier ('(' sil-argument (',' sil-argument)* ')')? ':'
sil-argument ::= sil-value-name ':' sil-type
sil-instruction-result ::= sil-value-name
sil-instruction-result ::= '(' (sil-value-name (',' sil-value-name)*)? ')'
sil-instruction-source-info ::= (',' sil-scope-ref)? (',' sil-loc)?
sil-instruction-def ::=
(sil-instruction-result '=')? sil-instruction sil-instruction-source-info
A function body consists of one or more basic blocks that correspond to the nodes of the function's control flow graph. Each basic block contains one or more instructions and ends with a terminator instruction. The function's entry point is always the first basic block in its body.
In SIL, basic blocks take arguments, which are used as an alternative to LLVM's phi nodes. Basic block arguments are bound by the branch from the predecessor block:
sil @iif : $(Builtin.Int1, Builtin.Int64, Builtin.Int64) -> Builtin.Int64 {
bb0(%cond : $Builtin.Int1, %ifTrue : $Builtin.Int64, %ifFalse : $Builtin.Int64):
cond_br %cond : $Builtin.Int1, then, else
then:
br finish(%ifTrue : $Builtin.Int64)
else:
br finish(%ifFalse : $Builtin.Int64)
finish(%result : $Builtin.Int64):
return %result : $Builtin.Int64
}
Arguments to the entry point basic block, which has no predecessor, are bound by the function's caller:
sil @foo : $(Int) -> Int {
bb0(%x : $Int):
return %x : $Int
}
sil @bar : $(Int, Int) -> () {
bb0(%x : $Int, %y : $Int):
%foo = function_ref @foo
%1 = apply %foo(%x) : $(Int) -> Int
%2 = apply %foo(%y) : $(Int) -> Int
%3 = tuple ()
return %3 : $()
}
sil-scope-ref ::= 'scope' [0-9]+
sil-scope ::= 'sil_scope' [0-9]+ '{'
sil-loc
'parent' scope-parent
('inlined_at' sil-scope-ref)?
'}'
scope-parent ::= sil-function-name ':' sil-type
scope-parent ::= sil-scope-ref
sil-loc ::= 'loc' string-literal ':' [0-9]+ ':' [0-9]+
Each instruction may have a debug location and a SIL scope reference at the end. Debug locations consist of a filename, a line number, and a column number. If the debug location is omitted, it defaults to the location in the SIL source file. SIL scopes describe the position inside the lexical scope structure that the Swift expression a SIL instruction was generated from had originally. SIL scopes also hold inlining information.
sil-decl-ref ::= '#' sil-identifier ('.' sil-identifier)* sil-decl-subref?
sil-decl-subref ::= '!' sil-decl-subref-part ('.' sil-decl-uncurry-level)? ('.' sil-decl-lang)?
sil-decl-subref ::= '!' sil-decl-uncurry-level ('.' sil-decl-lang)?
sil-decl-subref ::= '!' sil-decl-lang
sil-decl-subref-part ::= 'getter'
sil-decl-subref-part ::= 'setter'
sil-decl-subref-part ::= 'allocator'
sil-decl-subref-part ::= 'initializer'
sil-decl-subref-part ::= 'enumelt'
sil-decl-subref-part ::= 'destroyer'
sil-decl-subref-part ::= 'deallocator'
sil-decl-subref-part ::= 'globalaccessor'
sil-decl-subref-part ::= 'ivardestroyer'
sil-decl-subref-part ::= 'ivarinitializer'
sil-decl-subref-part ::= 'defaultarg' '.' [0-9]+
sil-decl-uncurry-level ::= [0-9]+
sil-decl-lang ::= 'foreign'
Some SIL instructions need to reference Swift declarations directly. These
references are introduced with the #
sigil followed by the fully qualified
name of the Swift declaration. Some Swift declarations are
decomposed into multiple entities at the SIL level. These are distinguished by
following the qualified name with !
and one or more .
-separated component
entity discriminators:
getter
: the getter function for avar
declarationsetter
: the setter function for avar
declarationallocator
: astruct
orenum
constructor, or aclass
's allocating constructorinitializer
: aclass
's initializing constructorenumelt
: a member of aenum
type.destroyer
: a class's destroying destructordeallocator
: a class's deallocating destructorglobalaccessor
: the addressor function for a global variableivardestroyer
: a class's ivar destroyerivarinitializer
: a class's ivar initializerdefaultarg.
n: the default argument-generating function for the n-th argument of a Swiftfunc
foreign
: a specific entry point for C/Objective-C interoperability
Methods and curried function definitions in Swift also have multiple "uncurry levels" in SIL, representing the function at each possible partial application level. For a curried function declaration:
// Module example
func foo(_ x:A)(y:B)(z:C) -> D
The declaration references and types for the different uncurry levels are as follows:
#example.foo!0 : $@convention(thin) (x:A) -> (y:B) -> (z:C) -> D
#example.foo!1 : $@convention(thin) ((y:B), (x:A)) -> (z:C) -> D
#example.foo!2 : $@convention(thin) ((z:C), (y:B), (x:A)) -> D
The deepest uncurry level is referred to as the natural uncurry level. In
this specific example, the reference at the natural uncurry level is
#example.foo!2
. Note that the uncurried argument clauses are composed
right-to-left, as specified in the calling convention. For uncurry levels
less than the uncurry level, the entry point itself is @convention(thin)
but
returns a thick function value carrying the partially applied arguments for its
context.
Dynamic dispatch instructions such as class method
require their method
declaration reference to be uncurried to at least uncurry level 1 (which applies
both the "self" argument and the method arguments), because uncurry level zero
represents the application of the method to its "self" argument, as in
foo.method
, which is where the dynamic dispatch semantically occurs
in Swift.
sil-linkage ::= 'public'
sil-linkage ::= 'hidden'
sil-linkage ::= 'shared'
sil-linkage ::= 'private'
sil-linkage ::= 'public_external'
sil-linkage ::= 'hidden_external'
sil-linkage ::= 'non_abi'
A linkage specifier controls the situations in which two objects in different SIL modules are linked, i.e. treated as the same object.
A linkage is external if it ends with the suffix external
. An
object must be a definition if its linkage is not external.
All functions, global variables, and witness tables have linkage.
The default linkage of a definition is public
. The default linkage of a
declaration is public_external
. (These may eventually change to hidden
and hidden_external
, respectively.)
On a global variable, an external linkage is what indicates that the
variable is not a definition. A variable lacking an explicit linkage
specifier is presumed a definition (and thus gets the default linkage
for definitions, public
.)
Two objects are linked if they have the same name and are mutually visible:
- An object with
public
orpublic_external
linkage is always visible.- An object with
hidden
,hidden_external
, orshared
linkage is visible only to objects in the same Swift module.- An object with
private
linkage is visible only to objects in the same SIL module.
Note that the linked relationship is an equivalence relation: it is reflexive, symmetric, and transitive.
If two objects are linked, they must have the same type.
If two objects are linked, they must have the same linkage, except:
- A
public
object may be linked to apublic_external
object.- A
hidden
object may be linked to ahidden_external
object.
If two objects are linked, at most one may be a definition, unless:
- both objects have
shared
linkage or- at least one of the objects has an external linkage.
If two objects are linked, and both are definitions, then the definitions must be semantically equivalent. This equivalence may exist only on the level of user-visible semantics of well-defined code; it should not be taken to guarantee that the linked definitions are exactly operationally equivalent. For example, one definition of a function might copy a value out of an address parameter, while another may have had an analysis applied to prove that said value is not needed.
If an object has any uses, then it must be linked to a definition with non-external linkage.
The non_abi linkage is a special linkage used for definitions which only exist in serialized SIL, and do not define visible symbols in the object file.
A definition with non_abi linkage behaves like it has shared linkage, except that it must be serialized in the SIL module even if not referenced from anywhere else in the module. For example, this means it is considered a root for dead function elimination.
When a non_abi definition is deserialized, it will have shared_external linkage.
There is no non_abi_external linkage. Instead, when referencing a non_abi declaration that is defined in a different translation unit from the same Swift module, you must use hidden_external linkage.
public
definitions are unique and visible everywhere in the program. In LLVM IR, they will be emitted withexternal
linkage anddefault
visibility.hidden
definitions are unique and visible only within the current Swift module. In LLVM IR, they will be emitted withexternal
linkage andhidden
visibility.private
definitions are unique and visible only within the current SIL module. In LLVM IR, they will be emitted withprivate
linkage.shared
definitions are visible only within the current Swift module. They can be linked only with othershared
definitions, which must be equivalent; therefore, they only need to be emitted if actually used. In LLVM IR, they will be emitted withlinkonce_odr
linkage andhidden
visibility.public_external
andhidden_external
objects always have visible definitions somewhere else. If this object nonetheless has a definition, it's only for the benefit of optimization or analysis. In LLVM IR, declarations will haveexternal
linkage and definitions (if actually emitted as definitions) will haveavailable_externally
linkage.
decl ::= sil-vtable
sil-vtable ::= 'sil_vtable' identifier '{' sil-vtable-entry* '}'
sil-vtable-entry ::= sil-decl-ref ':' sil-linkage? sil-function-name
SIL represents dynamic dispatch for class methods using the class_method, super_method, objc_method, and objc_super_method instructions.
The potential destinations for class_method and super_method are
tracked in sil_vtable
declarations for every class type. The declaration
contains a mapping from every method of the class (including those inherited
from its base class) to the SIL function that implements the method for that
class:
class A {
func foo()
func bar()
func bas()
}
sil @A_foo : $@convention(thin) (@owned A) -> ()
sil @A_bar : $@convention(thin) (@owned A) -> ()
sil @A_bas : $@convention(thin) (@owned A) -> ()
sil_vtable A {
#A.foo!1: @A_foo
#A.bar!1: @A_bar
#A.bas!1: @A_bas
}
class B : A {
func bar()
}
sil @B_bar : $@convention(thin) (@owned B) -> ()
sil_vtable B {
#A.foo!1: @A_foo
#A.bar!1: @B_bar
#A.bas!1: @A_bas
}
class C : B {
func bas()
}
sil @C_bas : $@convention(thin) (@owned C) -> ()
sil_vtable C {
#A.foo!1: @A_foo
#A.bar!1: @B_bar
#A.bas!1: @C_bas
}
Note that the declaration reference in the vtable is to the least-derived method
visible through that class (in the example above, B
's vtable references
A.bar
and not B.bar
, and C
's vtable references A.bas
and not
C.bas
). The Swift AST maintains override relationships between declarations
that can be used to look up overridden methods in the SIL vtable for a derived
class (such as C.bas
in C
's vtable).
In case the SIL function is a thunk, the function name is preceded with the linkage of the original implementing function.
decl ::= sil-witness-table
sil-witness-table ::= 'sil_witness_table' sil-linkage?
normal-protocol-conformance '{' sil-witness-entry* '}'
SIL encodes the information needed for dynamic dispatch of generic types into witness tables. This information is used to produce runtime dispatch tables when generating binary code. It can also be used by SIL optimizations to specialize generic functions. A witness table is emitted for every declared explicit conformance. Generic types share one generic witness table for all of their instances. Derived classes inherit the witness tables of their base class.
protocol-conformance ::= normal-protocol-conformance
protocol-conformance ::= 'inherit' '(' protocol-conformance ')'
protocol-conformance ::= 'specialize' '<' substitution* '>'
'(' protocol-conformance ')'
protocol-conformance ::= 'dependent'
normal-protocol-conformance ::= identifier ':' identifier 'module' identifier
Witness tables are keyed by protocol conformance, which is a unique identifier for a concrete type's conformance to a protocol.
- A normal protocol conformance names a (potentially unbound generic) type, the protocol it conforms to, and the module in which the type or extension declaration that provides the conformance appears. These correspond 1:1 to protocol conformance declarations in the source code.
- If a derived class conforms to a protocol through inheritance from its base class, this is represented by an inherited protocol conformance, which simply references the protocol conformance for the base class.
- If an instance of a generic type conforms to a protocol, it does so with a specialized conformance, which provides the generic parameter bindings to the normal conformance, which should be for a generic type.
Witness tables are only directly associated with normal conformances. Inherited and specialized conformances indirectly reference the witness table of the underlying normal conformance.
sil-witness-entry ::= 'base_protocol' identifier ':' protocol-conformance
sil-witness-entry ::= 'method' sil-decl-ref ':' sil-function-name
sil-witness-entry ::= 'associated_type' identifier
sil-witness-entry ::= 'associated_type_protocol'
'(' identifier ':' identifier ')' ':' protocol-conformance
Witness tables consist of the following entries:
- Base protocol entries provide references to the protocol conformances that satisfy the witnessed protocols' inherited protocols.
- Method entries map a method requirement of the protocol to a SIL function that implements that method for the witness type. One method entry must exist for every required method of the witnessed protocol.
- Associated type entries map an associated type requirement of the protocol to the type that satisfies that requirement for the witness type. Note that the witness type is a source-level Swift type and not a SIL type. One associated type entry must exist for every required associated type of the witnessed protocol.
- Associated type protocol entries map a protocol requirement on an associated type to the protocol conformance that satisfies that requirement for the associated type.
decl ::= sil-default-witness-table
sil-default-witness-table ::= 'sil_default_witness_table'
identifier minimum-witness-table-size
'{' sil-default-witness-entry* '}'
minimum-witness-table-size ::= integer
SIL encodes requirements with resilient default implementations in a default witness table. We say a requirement has a resilient default implementation if the following conditions hold:
- The requirement has a default implementation
- The requirement is either the last requirement in the protocol, or all subsequent requirements also have resilient default implementations
The set of requirements with resilient default implementations is stored in protocol metadata.
The minimum witness table size is the size of the witness table, in words, not including any requirements with resilient default implementations.
Any conforming witness table must have a size between the minimum size, and the maximum size, which is equal to the minimum size plus the number of default requirements.
At load time, if the runtime encounters a witness table with fewer than the maximum number of witnesses, the witness table is copied, with default witnesses copied in. This ensures that callers can always expect to find the correct number of requirements in each witness table, and new requirements can be added by the framework author, without breaking client code, as long as the new requirements have resilient default implementations.
Default witness tables are keyed by the protocol itself. Only protocols with public visibility need a default witness table; private and internal protocols are never seen outside the module, therefore there are no resilience issues with adding new requirements.
sil-default-witness-entry ::= 'method' sil-decl-ref ':' sil-function-name
Default witness tables currently contain only one type of entry:
- Method entries map a method requirement of the protocol to a SIL function that implements that method in a manner suitable for all witness types.
decl ::= sil-global-variable
static-initializer ::= '=' '{' sil-instruction-def* '}'
sil-global-variable ::= 'sil_global' sil-linkage identifier ':' sil-type
(static-initializer)?
SIL representation of a global variable.
Global variable access is performed by the alloc_global
, global_addr
and global_value
instructions.
A global can have a static initializer if its initial value can be composed of literals. The static initializer is represented as a list of literal and aggregate instructions where the last instruction is the top-level value of the static initializer:
sil_global hidden @$S4test3varSiv : $Int {
%0 = integer_literal $Builtin.Int64, 27
%initval = struct $Int (%0 : $Builtin.Int64)
}
If a global does not have a static initializer, the alloc_global
instruction must be performed prior an access to initialize the storage.
Once a global's storage has been initialized, global_addr
is used to
project the value.
If the last instruction in the static initializer is an object
instruction
the global variable is a statically initialized object. In this case the
variable cannot be used as l-value, i.e. the reference to the object cannot be
modified. As a consequence the variable cannot be accessed with global_addr
but only with global_value
.
Dataflow errors may exist in raw SIL. Swift's semantics defines these conditions as errors, so they must be diagnosed by diagnostic passes and must not exist in canonical SIL.
Swift requires that all local variables be initialized before use. In constructors, all instance variables of a struct, enum, or class type must be initialized before the object is used and before the constructor is returned from.
The unreachable
terminator is emitted in raw SIL to mark incorrect control
flow, such as a non-Void
function failing to return
a value, or a
switch
statement failing to cover all possible values of its subject.
The guaranteed dead code elimination pass can eliminate truly unreachable
basic blocks, or unreachable
instructions may be dominated by applications
of functions returning uninhabited types. An unreachable
instruction that
survives guaranteed DCE and is not immediately preceded by a no-return
application is a dataflow error.
Some operations, such as failed unconditional checked conversions or the
Builtin.trap
compiler builtin, cause a runtime failure, which
unconditionally terminates the current actor. If it can be proven that a
runtime failure will occur or did occur, runtime failures may be reordered so
long as they remain well-ordered relative to operations external to the actor
or the program as a whole. For instance, with overflow checking on integer
arithmetic enabled, a simple for
loop that reads inputs in from one or more
arrays and writes outputs to another array, all local
to the current actor, may cause runtime failure in the update operations:
// Given unknown start and end values, this loop may overflow
for var i = unknownStartValue; i != unknownEndValue; ++i {
...
}
It is permitted to hoist the overflow check and associated runtime failure out of the loop itself and check the bounds of the loop prior to entering it, so long as the loop body has no observable effect outside of the current actor.
Incorrect use of some operations is undefined behavior, such as invalid
unchecked casts involving Builtin.RawPointer
types, or use of compiler
builtins that lower to LLVM instructions with undefined behavior at the LLVM
level. A SIL program with undefined behavior is meaningless, much like undefined
behavior in C, and has no predictable semantics. Undefined behavior should not
be triggered by valid SIL emitted by a correct Swift program using a correct
standard library, but cannot in all cases be diagnosed or verified at the SIL
level.
This section describes how Swift functions are emitted in SIL.
The Swift calling convention is the one used by default for native Swift functions.
Tuples in the input type of the function are recursively destructured into
separate arguments, both in the entry point basic block of the callee, and
in the apply
instructions used by callers:
func foo(_ x:Int, y:Int)
sil @foo : $(x:Int, y:Int) -> () {
entry(%x : $Int, %y : $Int):
...
}
func bar(_ x:Int, y:(Int, Int))
sil @bar : $(x:Int, y:(Int, Int)) -> () {
entry(%x : $Int, %y0 : $Int, %y1 : $Int):
...
}
func call_foo_and_bar() {
foo(1, 2)
bar(4, (5, 6))
}
sil @call_foo_and_bar : $() -> () {
entry:
...
%foo = function_ref @foo : $(x:Int, y:Int) -> ()
%foo_result = apply %foo(%1, %2) : $(x:Int, y:Int) -> ()
...
%bar = function_ref @bar : $(x:Int, y:(Int, Int)) -> ()
%bar_result = apply %bar(%4, %5, %6) : $(x:Int, y:(Int, Int)) -> ()
}
Calling a function with trivial value types as inputs and outputs simply passes the arguments by value. This Swift function:
func foo(_ x:Int, y:Float) -> UnicodeScalar
foo(x, y)
gets called in SIL as:
%foo = constant_ref $(Int, Float) -> UnicodeScalar, @foo
%z = apply %foo(%x, %y) : $(Int, Float) -> UnicodeScalar
NOTE This section only is speaking in terms of rules of thumb. The
actual behavior of arguments with respect to arguments is defined by
the argument's convention attribute (e.g. @owned
), not the
calling convention itself.
Reference type arguments are passed in at +1 retain count and consumed by the callee. A reference type return value is returned at +1 and consumed by the caller. Value types with reference type components have their reference type components each retained and released the same way. This Swift function:
class A {}
func bar(_ x:A) -> (Int, A) { ... }
bar(x)
gets called in SIL as:
%bar = function_ref @bar : $(A) -> (Int, A)
strong_retain %x : $A
%z = apply %bar(%x) : $(A) -> (Int, A)
// ... use %z ...
%z_1 = tuple_extract %z : $(Int, A), 1
strong_release %z_1
When applying a thick function value as a callee, the function value is also consumed at +1 retain count.
For address-only arguments, the caller allocates a copy and passes the address of the copy to the callee. The callee takes ownership of the copy and is responsible for destroying or consuming the value, though the caller must still deallocate the memory. For address-only return values, the caller allocates an uninitialized buffer and passes its address as the first argument to the callee. The callee must initialize this buffer before returning. This Swift function:
@API struct A {}
func bas(_ x:A, y:Int) -> A { return x }
var z = bas(x, y)
// ... use z ...
gets called in SIL as:
%bas = function_ref @bas : $(A, Int) -> A
%z = alloc_stack $A
%x_arg = alloc_stack $A
copy_addr %x to [initialize] %x_arg : $*A
apply %bas(%z, %x_arg, %y) : $(A, Int) -> A
dealloc_stack %x_arg : $*A // callee consumes %x.arg, caller deallocs
// ... use %z ...
destroy_addr %z : $*A
dealloc_stack stack %z : $*A
The implementation of @bas
is then responsible for consuming %x_arg
and
initializing %z
.
Tuple arguments are destructured regardless of the address-only-ness of the tuple type. The destructured fields are passed individually according to the above convention. This Swift function:
@API struct A {}
func zim(_ x:Int, y:A, (z:Int, w:(A, Int)))
zim(x, y, (z, w))
gets called in SIL as:
%zim = function_ref @zim : $(x:Int, y:A, (z:Int, w:(A, Int))) -> ()
%y_arg = alloc_stack $A
copy_addr %y to [initialize] %y_arg : $*A
%w_0_addr = element_addr %w : $*(A, Int), 0
%w_0_arg = alloc_stack $A
copy_addr %w_0_addr to [initialize] %w_0_arg : $*A
%w_1_addr = element_addr %w : $*(A, Int), 1
%w_1 = load %w_1_addr : $*Int
apply %zim(%x, %y_arg, %z, %w_0_arg, %w_1) : $(x:Int, y:A, (z:Int, w:(A, Int))) -> ()
dealloc_stack %w_0_arg
dealloc_stack %y_arg
Variadic arguments and tuple elements are packaged into an array and passed as a single array argument. This Swift function:
func zang(_ x:Int, (y:Int, z:Int...), v:Int, w:Int...)
zang(x, (y, z0, z1), v, w0, w1, w2)
gets called in SIL as:
%zang = function_ref @zang : $(x:Int, (y:Int, z:Int...), v:Int, w:Int...) -> ()
%zs = <<make array from %z1, %z2>>
%ws = <<make array from %w0, %w1, %w2>>
apply %zang(%x, %y, %zs, %v, %ws) : $(x:Int, (y:Int, z:Int...), v:Int, w:Int...) -> ()
Curried function definitions in Swift emit multiple SIL entry points, one for each "uncurry level" of the function. When a function is uncurried, its outermost argument clauses are combined into a tuple in right-to-left order. For the following declaration:
func curried(_ x:A)(y:B)(z:C)(w:D) -> Int {}
The types of the SIL entry points are as follows:
sil @curried_0 : $(x:A) -> (y:B) -> (z:C) -> (w:D) -> Int { ... }
sil @curried_1 : $((y:B), (x:A)) -> (z:C) -> (w:D) -> Int { ... }
sil @curried_2 : $((z:C), (y:B), (x:A)) -> (w:D) -> Int { ... }
sil @curried_3 : $((w:D), (z:C), (y:B), (x:A)) -> Int { ... }
@inout
arguments are passed into the entry point by address. The callee
does not take ownership of the referenced memory. The referenced memory must
be initialized upon function entry and exit. If the @inout
argument
refers to a fragile physical variable, then the argument is the address of that
variable. If the @inout
argument refers to a logical property, then the
argument is the address of a caller-owned writeback buffer. It is the caller's
responsibility to initialize the buffer by storing the result of the property
getter prior to calling the function and to write back to the property
on return by loading from the buffer and invoking the setter with the final
value. This Swift function:
func inout(_ x: inout Int) {
x = 1
}
gets lowered to SIL as:
sil @inout : $(@inout Int) -> () {
entry(%x : $*Int):
%1 = integer_literal $Int, 1
store %1 to %x
return
}
The method calling convention is currently identical to the freestanding function convention. Methods are considered to be curried functions, taking the "self" argument as their outer argument clause, and the method arguments as the inner argument clause(s). When uncurried, the "self" argument is thus passed last:
struct Foo {
func method(_ x:Int) -> Int {}
}
sil @Foo_method_1 : $((x : Int), @inout Foo) -> Int { ... }
The witness method calling convention is used by protocol witness methods in
witness tables. It is identical to the method
calling convention
except that its handling of generic type parameters. For non-witness methods,
the machine-level convention for passing type parameter metadata may be
arbitrarily dependent on static aspects of the function signature, but because
witnesses must be polymorphically dispatchable on their Self
type,
the Self
-related metadata for a witness must be passed in a maximally
abstracted manner.
In Swift's C module importer, C types are always mapped to Swift types considered trivial by SIL. SIL does not concern itself with platform ABI requirements for indirect return, register vs. stack passing, etc.; C function arguments and returns in SIL are always by value regardless of the platform calling convention.
SIL (and therefore Swift) cannot currently invoke variadic C functions.
Objective-C methods use the same argument and return value ownership rules as
ARC Objective-C. Selector families and the ns_consumed
,
ns_returns_retained
, etc. attributes from imported Objective-C definitions
are honored.
Applying a @convention(block)
value does not consume the block.
In SIL, the "self" argument of an Objective-C method is uncurried to the last argument of the uncurried type, just like a native Swift method:
@objc class NSString {
func stringByPaddingToLength(Int) withString(NSString) startingAtIndex(Int)
}
sil @NSString_stringByPaddingToLength_withString_startingAtIndex \
: $((Int, NSString, Int), NSString)
That self
is passed as the first argument at the IR level is abstracted
away in SIL, as is the existence of the _cmd
selector argument.
SIL supports two types of Type Based Alias Analysis (TBAA): Class TBAA and Typed Access TBAA.
Class instances and other heap object references are pointers at the
implementation level, but unlike SIL addresses, they are first class values and
can be capture
-d and aliased. Swift, however, is memory-safe and statically
typed, so aliasing of classes is constrained by the type system as follows:
- A
Builtin.NativeObject
may alias any native Swift heap object, including a Swift class instance, a box allocated byalloc_box
, or a thick function's closure context. It may not alias natively Objective-C class instances. - An
AnyObject
orBuiltin.BridgeObject
may alias any class instance, whether Swift or Objective-C, but may not alias non-class-instance heap objects. - Two values of the same class type
$C
may alias. Two values of related class type$B
and$D
, where there is a subclass relationship between$B
and$D
, may alias. Two values of unrelated class types may not alias. This includes different instantiations of a generic class type, such as$C<Int>
and$C<Float>
, which currently may never alias. - Without whole-program visibility, values of archetype or protocol type must
be assumed to potentially alias any class instance. Even if it is locally
apparent that a class does not conform to that protocol, another component
may introduce a conformance by an extension. Similarly, a generic class
instance, such as
$C<T>
for archetypeT
, must be assumed to potentially alias concrete instances of the generic type, such as$C<Int>
, becauseInt
is a potential substitution forT
.
A violation of the above aliasing rules only results in undefined
behavior if the aliasing references are dereferenced within Swift code.
For example,
__SwiftNativeNS[Array|Dictionary|String]
classes alias with
NS[Array|Dictionary|String]
classes even though they are not
statically related. Since Swift never directly accesses stored
properties on the Foundation classes, this aliasing does not pose a
danger.
Define a typed access of an address or reference as one of the following:
- Any instruction that performs a typed read or write operation upon the memory
at the given location (e.x.
load
,store
). - Any instruction that yields a typed offset of the pointer by performing a
typed projection operation (e.x.
ref_element_addr
,tuple_element_addr
).
With limited exceptions, it is undefined behavior to perform a typed access to an address or reference addressed memory is not bound to the relevant type.
This allows the optimizer to assume that two addresses cannot alias if there does not exist a substitution of archetypes that could cause one of the types to be the type of a subobject of the other. Additionally, this applies to the types of the values from which the addresses were derived via a typed projection.
Consider the following SIL:
struct Element {
var i: Int
}
struct S1 {
var elt: Element
}
struct S2 {
var elt: Element
}
%adr1 = struct_element_addr %ptr1 : $*S1, #S.elt
%adr2 = struct_element_addr %ptr2 : $*S2, #S.elt
The optimizer may assume that %adr1
does not alias with %adr2
because the values that the addresses are derived from (%ptr1
and
%ptr2
) have unrelated types. However, in the following example,
the optimizer cannot assume that %adr1
does not alias with
%adr2
because %adr2
is derived from a cast, and any subsequent
typed operations on the address will refer to the common Element
type:
%adr1 = struct_element_addr %ptr1 : $*S1, #S.elt
%adr2 = pointer_to_address %ptr2 : $Builtin.RawPointer to $*Element
Exceptions to typed access TBAA rules are only allowed for blessed
alias-introducing operations. This permits limited type-punning. The only
current exception is the non-struct pointer_to_address
variant. The
optimizer must be able to defensively determine that none of the roots of an
address are alias-introducing operations. An address root is the operation that
produces the address prior to applying any typed projections, indexing, or
casts. The following are valid address roots:
- Object allocation that generates an address, such as
alloc_stack
andalloc_box
. - Address-type function arguments. These are crucially not considered alias-introducing operations. It is illegal for the SIL optimizer to form a new function argument from an arbitrary address-type value. Doing so would require the optimizer to guarantee that the new argument is both has a non-alias-introducing address root and can be properly represented by the calling convention (address types do not have a fixed representation).
- A strict cast from an untyped pointer,
pointer_to_address [strict]
. It is illegal forpointer_to_address [strict]
to derive its address from an alias-introducing operation's value. A type punned address may only be produced from an opaque pointer via a non-strictpointer_to_address
at the point of conversion.
Address-to-address casts, via unchecked_addr_cast
, transparently
forward their source's address root, just like typed projections.
Address-type basic block arguments can be conservatively considered aliasing-introducing operations; they are uncommon enough not to matter and may eventually be prohibited altogether.
Although some pointer producing intrinsics exist, they do not need to be
considered alias-introducing exceptions to TBAA rules. Builtin.inttoptr
produces a Builtin.RawPointer
which is not interesting because by definition
it may alias with everything. Similarly, the LLVM builtins Builtin.bitcast
and Builtin.trunc|sext|zextBitCast
cannot produce typed pointers. These
pointer values must be converted to an address via pointer_to_address
before
typed access can occur. Whether the pointer_to_address
is strict determines
whether aliasing may occur.
Memory may be rebound to an unrelated type. Addresses to unrelated types may alias as long as typed access only occurs while memory is bound to the relevant type. Consequently, the optimizer cannot outright assume that addresses accessed as unrelated types are nonaliasing. For example, pointer comparison cannot be eliminated simply because the two addresses derived from those pointers are accessed as unrelated types at different program points.
In general, analyses can assume that independent values are independently assured of validity. For example, a class method may return a class reference:
bb0(%0 : $MyClass):
%1 = class_method %0 : $MyClass, #MyClass.foo!1
%2 = apply %1(%0) : $@convention(method) (@guaranteed MyClass) -> @owned MyOtherClass
// use of %2 goes here; no use of %1
strong_release %2 : $MyOtherClass
strong_release %1 : $MyClass
The optimizer is free to move the release of %1
to immediately
after the call here, because %2
can be assumed to be an
independently-managed value, and because Swift generally permits the
reordering of destructors.
However, some instructions do create values that are intrinsically
dependent on their operands. For example, the result of
ref_element_addr
will become a dangling pointer if the base is
released too soon. This is captured by the concept of value dependence,
and any transformation which can reorder of destruction of a value
around another operation must remain conscious of it.
A value %1
is said to be value-dependent on a value %0
if:
%1
is the result and%0
is the first operand of one of the following instructions:ref_element_addr
struct_element_addr
tuple_element_addr
unchecked_take_enum_data_addr
pointer_to_address
address_to_pointer
index_addr
index_raw_pointer
- possibly some other conversions
%1
is the result ofmark_dependence
and%0
is either of the operands.%1
is the value address of a box allocation instruction of which%0
is the box reference.%1
is the result of astruct
,tuple
, orenum
instruction and%0
is an operand.%1
is the result of projecting out a subobject of%0
withtuple_extract
,struct_extract
,unchecked_enum_data
,select_enum
, orselect_enum_addr
.%1
is the result ofselect_value
and%0
is one of the cases.%1
is a basic block parameter and%0
is the corresponding argument from a branch to that block.%1
is the result of aload
from%0
. However, the value dependence is cut after the first attempt to manage the value of%1
, e.g. by retaining it.- Transitivity: there exists a value
%2
which%1
depends on and which depends on%0
. However, transitivity does not apply to different subobjects of a struct, tuple, or enum.
Note, however, that an analysis is not required to track dependence
through memory. Nor is it required to consider the possibility of
dependence being established "behind the scenes" by opaque code, such
as by a method returning an unsafe pointer to a class property. The
dependence is required to be locally obvious in a function's SIL
instructions. Precautions must be taken against this either by SIL
generators (by using mark_dependence
appropriately) or by the user
(by using the appropriate intrinsics and attributes with unsafe
language or library features).
Only certain types of SIL value can carry value-dependence:
- SIL address types
- unmanaged pointer types:
@sil_unmanaged
typesBuiltin.RawPointer
- aggregates containing such a type, such as
UnsafePointer
, possibly recursively
- non-trivial types (but they can be independently managed)
This rule means that casting a pointer to an integer type breaks
value-dependence. This restriction is necessary so that reading an
Int
from a class doesn't force the class to be kept around!
A class holding an unsafe reference to an object must use some
sort of unmanaged pointer type to do so.
This rule does not include generic or resilient value types which
might contain unmanaged pointer types. Analyses are free to assume
that e.g. a copy_addr
of a generic or resilient value type yields
an independently-managed value. The extension of value dependence to
types containing obvious unmanaged pointer types is an affordance to
make the use of such types more convenient; it does not shift the
ultimate responsibility for assuring the safety of unsafe
language/library features away from the user.
These instructions allocate and deallocate memory.
sil-instruction ::= 'alloc_stack' sil-type (',' debug-var-attr)*
%1 = alloc_stack $T
// %1 has type $*T
Allocates uninitialized memory that is sufficiently aligned on the stack
to contain a value of type T
. The result of the instruction is the address
of the allocated memory.
If a type is runtime-sized, the compiler must emit code to potentially dynamically allocate memory. So there is no guarantee that the allocated memory is really located on the stack.
alloc_stack
marks the start of the lifetime of the value; the
allocation must be balanced with a dealloc_stack
instruction to
mark the end of its lifetime. All alloc_stack
allocations must be
deallocated prior to returning from a function. If a block has multiple
predecessors, the stack height and order of allocations must be consistent
coming from all predecessor blocks. alloc_stack
allocations must be
deallocated in last-in, first-out stack order.
The memory is not retainable. To allocate a retainable box for a value
type, use alloc_box
.
sil-instruction ::= 'alloc_ref'
('[' 'objc' ']')?
('[' 'stack' ']')?
('[' 'tail_elems' sil-type '*' sil-operand ']')*
sil-type
%1 = alloc_ref [stack] $T
%1 = alloc_ref [tail_elems $E * %2 : Builtin.Word] $T
// $T must be a reference type
// %1 has type $T
// $E is the type of the tail-allocated elements
// %2 must be of a builtin integer type
Allocates an object of reference type T
. The object will be initialized
with retain count 1; its state will be otherwise uninitialized. The
optional objc
attribute indicates that the object should be
allocated using Objective-C's allocation methods (+allocWithZone:
).
The optional stack
attribute indicates that the object can be allocated
on the stack instead on the heap. In this case the instruction must have
balanced with a dealloc_ref [stack]
instruction to mark the end of the
object's lifetime.
Note that the stack
attribute only specifies that stack allocation is
possible. The final decision on stack allocation is done during llvm IR
generation. This is because the decision also depends on the object size,
which is not necessarily known at SIL level.
The optional tail_elems
attributes specifies the amount of space to be
reserved for tail-allocated arrays of given element types and element counts.
If there are more than one tail_elems
attributes then the tail arrays are
allocated in the specified order.
The count-operand must be of a builtin integer type.
The instructions ref_tail_addr
and tail_addr
can be used to project
the tail elements.
The objc
attribute cannot be used together with tail_elems
.
sil-instruction ::= 'alloc_ref_dynamic'
('[' 'objc' ']')?
('[' 'tail_elems' sil-type '*' sil-operand ']')*
sil-operand ',' sil-type
%1 = alloc_ref_dynamic %0 : $@thick T.Type, $T
%1 = alloc_ref_dynamic [objc] %0 : $@objc_metatype T.Type, $T
%1 = alloc_ref_dynamic [tail_elems $E * %2 : Builtin.Word] %0 : $@thick T.Type, $T
// $T must be a class type
// %1 has type $T
// $E is the type of the tail-allocated elements
// %2 must be of a builtin integer type
Allocates an object of class type T
or a subclass thereof. The
dynamic type of the resulting object is specified via the metatype
value %0
. The object will be initialized with retain count 1; its
state will be otherwise uninitialized.
The optional tail_elems
and objc
attributes have the same effect as
for alloc_ref
. See alloc_ref
for details.
sil-instruction ::= 'alloc_box' sil-type (',' debug-var-attr)*
%1 = alloc_box $T
// %1 has type $@box T
Allocates a reference-counted @box
on the heap large enough to hold a value
of type T
, along with a retain count and any other metadata required by the
runtime. The result of the instruction is the reference-counted @box
reference that owns the box. The project_box
instruction is used to retrieve
the address of the value inside the box.
The box will be initialized with a retain count of 1; the storage will be
uninitialized. The box owns the contained value, and releasing it to a retain
count of zero destroys the contained value as if by destroy_addr
.
Releasing a box is undefined behavior if the box's value is uninitialized.
To deallocate a box whose value has not been initialized, dealloc_box
should be used.
sil-instruction ::= 'alloc_value_buffer' sil-type 'in' sil-operand
%1 = alloc_value_buffer $(Int, T) in %0 : $*Builtin.UnsafeValueBuffer
// The operand must have the exact type shown.
// The result has type $*(Int, T).
Given the address of an unallocated value buffer, allocate space in it for a value of the given type. This instruction has undefined behavior if the value buffer is currently allocated.
The type operand must be a lowered object type.
sil-instruction ::= 'alloc_global' sil-global-name
alloc_global @foo
Initialize the storage for a global variable. This instruction has undefined behavior if the global variable has already been initialized.
The type operand must be a lowered object type.
sil-instruction ::= 'dealloc_stack' sil-operand
dealloc_stack %0 : $*T
// %0 must be of $*T type
Deallocates memory previously allocated by alloc_stack
. The
allocated value in memory must be uninitialized or destroyed prior to
being deallocated. This instruction marks the end of the lifetime for
the value created by the corresponding alloc_stack
instruction. The operand
must be the shallowest live alloc_stack
allocation preceding the
deallocation. In other words, deallocations must be in last-in, first-out
stack order.
sil-instruction ::= 'dealloc_box' sil-operand
dealloc_box %0 : $@box T
Deallocates a box, bypassing the reference counting mechanism. The box
variable must have a retain count of one. The boxed type must match the
type passed to the corresponding alloc_box
exactly, or else
undefined behavior results.
This does not destroy the boxed value. The contents of the
value must have been fully uninitialized or destroyed before
dealloc_box
is applied.
sil-instruction ::= 'project_box' sil-operand
%1 = project_box %0 : $@box T
// %1 has type $*T
Given a @box T
reference, produces the address of the value inside the box.
sil-instruction ::= 'dealloc_ref' ('[' 'stack' ']')? sil-operand
dealloc_ref [stack] %0 : $T
// $T must be a class type
Deallocates an uninitialized class type instance, bypassing the reference counting mechanism.
The type of the operand must match the allocated type exactly, or else undefined behavior results.
The instance must have a retain count of one.
This does not destroy stored properties of the instance. The contents
of stored properties must be fully uninitialized at the time
dealloc_ref
is applied.
The stack
attribute indicates that the instruction is the balanced
deallocation of its operand which must be a alloc_ref [stack]
.
In this case the instruction marks the end of the object's lifetime but
has no other effect.
sil-instruction ::= 'dealloc_partial_ref' sil-operand sil-metatype
dealloc_partial_ref %0 : $T, %1 : $U.Type
// $T must be a class type
// $T must be a subclass of U
Deallocates a partially-initialized class type instance, bypassing the reference counting mechanism.
The type of the operand must be a supertype of the allocated type, or else undefined behavior results.
The instance must have a retain count of one.
All stored properties in classes more derived than the given metatype value must be initialized, and all other stored properties must be uninitialized. The initialized stored properties are destroyed before deallocating the memory for the instance.
This does not destroy the reference type instance. The contents of the
heap object must have been fully uninitialized or destroyed before
dealloc_ref
is applied.
sil-instruction ::= 'dealloc_value_buffer' sil-type 'in' sil-operand
dealloc_value_buffer $(Int, T) in %0 : $*Builtin.UnsafeValueBuffer
// The operand must have the exact type shown.
Given the address of a value buffer, deallocate the storage in it. This instruction has undefined behavior if the value buffer is not currently allocated, or if it was allocated with a type other than the type operand.
The type operand must be a lowered object type.
sil-instruction ::= 'project_value_buffer' sil-type 'in' sil-operand
%1 = project_value_buffer $(Int, T) in %0 : $*Builtin.UnsafeValueBuffer
// The operand must have the exact type shown.
// The result has type $*(Int, T).
Given the address of a value buffer, return the address of the value storage in it. This instruction has undefined behavior if the value buffer is not currently allocated, or if it was allocated with a type other than the type operand.
The result is the same value as was originally returned by
alloc_value_buffer
.
The type operand must be a lowered object type.
Debug information is generally associated with allocations (alloc_stack or alloc_box) by having a Decl node attached to the allocation with a SILLocation. For declarations that have no allocation we have explicit instructions for doing this. This is used by 'let' declarations, which bind a value to a name and for var decls who are promoted into registers. The decl they refer to is attached to the instruction with a SILLocation.
sil-instruction ::= debug_value sil-operand (',' debug-var-attr)*
debug_value %1 : $Int
This indicates that the value of a declaration with loadable type has changed value to the specified operand. The declaration in question is identified by the SILLocation attached to the debug_value instruction.
The operand must have loadable type.
debug-var-attr ::= 'var'
debug-var-attr ::= 'let'
debug-var-attr ::= 'name' string-literal
debug-var-attr ::= 'argno' integer-literal
There are a number of attributes that provide details about the source
variable that is being described, including the name of the
variable. For function and closure arguments argno
is the number
of the function argument starting with 1.
sil-instruction ::= debug_value_addr sil-operand (',' debug-var-attr)*
debug_value_addr %7 : $*SomeProtocol
This indicates that the value of a declaration with address-only type has changed value to the specified operand. The declaration in question is identified by the SILLocation attached to the debug_value_addr instruction.
sil-instruction ::= 'load' sil-operand
%1 = load %0 : $*T
// %0 must be of a $*T address type for loadable type $T
// %1 will be of type $T
Loads the value at address %0
from memory. T
must be a loadable type.
This does not affect the reference count, if any, of the loaded value; the
value must be retained explicitly if necessary. It is undefined behavior to
load from uninitialized memory or to load from an address that points to
deallocated storage.
sil-instruction ::= 'store' sil-value 'to' sil-operand
store %0 to %1 : $*T
// $T must be a loadable type
Stores the value %0
to memory at address %1
. The type of %1 is *T
and the type of %0
is T
, which must be a loadable type. This will
overwrite the memory at %1
. If %1
already references a value that
requires release
or other cleanup, that value must be loaded before being
stored over and cleaned up. It is undefined behavior to store to an address
that points to deallocated storage.
sil-instruction ::= 'load_borrow' sil-value
%1 = load_borrow %0 : $*T
// $T must be a loadable type
Loads the value %1
from the memory location %0
. The load_borrow
instruction creates a borrowed scope in which a read-only borrow value %1
can be used to read the value stored in %0
. The end of scope is delimited
by an end_borrow
instruction. All load_borrow
instructions must be
paired with exactly one end_borrow
instruction along any path through the
program. Until end_borrow
, it is illegal to invalidate or store to %0
.
sil-instruction ::= 'end_borrow' sil-value 'from' sil-value : sil-type, sil-type
end_borrow %1 from %0 : $T, $T
end_borrow %1 from %0 : $T, $*T
end_borrow %1 from %0 : $*T, $T
end_borrow %1 from %0 : $*T, $*T
// We allow for end_borrow to be specified in between values and addresses
// all of the same type T.
Ends the scope for which the SILValue %1
is borrowed from the SILValue
%0
. Must be paired with at most 1 borrowing instruction (like
load_borrow
) along any path through the program. In the region in between
the borrow instruction and the end_borrow
, the original SILValue can not be
modified. This means that:
- If
%0
is an address,%0
can not be written to. - If
%0
is a non-trivial value,%0
can not be destroyed.
We require that %1
and %0
have the same type ignoring SILValueCategory.
sil-instruction ::= 'assign' sil-value 'to' sil-operand
assign %0 to %1 : $*T
// $T must be a loadable type
Represents an abstract assignment of the value %0
to memory at address
%1
without specifying whether it is an initialization or a normal store.
The type of %1 is *T
and the type of %0
is T
, which must be a
loadable type. This will overwrite the memory at %1
and destroy the value
currently held there.
The purpose of the assign
instruction is to simplify the
definitive initialization analysis on loadable variables by removing
what would otherwise appear to be a load and use of the current value.
It is produced by SILGen, which cannot know which assignments are
meant to be initializations. If it is deemed to be an initialization,
it can be replaced with a store
; otherwise, it must be replaced
with a sequence that also correctly destroys the current value.
This instruction is only valid in Raw SIL and is rewritten as appropriate by the definitive initialization pass.
sil-instruction ::= 'assign_by_wrapper' sil-operand 'to' sil-operand ',' 'init' sil-operand ',' 'set' sil-operand
assign_by_wrapper %0 : $S to %1 : $*T, init %2 : $F, set %3 : $G
// $S can be a value or address type
// $T must be the type of a property wrapper.
// $F must be a function type, taking $S as a single argument and returning $T
// $G must be a function type, taking $S as a single argument and with not return value
Similar to the assign
instruction, but the assignment is done via a
delegate.
In case of an initialization, the function %2
is called with %0
as
argument. The result is stored to %1
. In case %2
is an address type,
it is simply passed as a first out-argument to %2
.
In case of a re-assignment, the function %3
is called with %0
as
argument. As %3
is a setter (e.g. for the property in the containing
nominal type), the destination address %1
is not used in this case.
This instruction is only valid in Raw SIL and is rewritten as appropriate by the definitive initialization pass.
sil-instruction ::= 'mark_uninitialized' '[' mu_kind ']' sil-operand
mu_kind ::= 'var'
mu_kind ::= 'rootself'
mu_kind ::= 'crossmodulerootself'
mu_kind ::= 'derivedself'
mu_kind ::= 'derivedselfonly'
mu_kind ::= 'delegatingself'
mu_kind ::= 'delegatingselfallocated'
%2 = mark_uninitialized [var] %1 : $*T
// $T must be an address
Indicates that a symbolic memory location is uninitialized, and must be explicitly initialized before it escapes or before the current function returns. This instruction returns its operands, and all accesses within the function must be performed against the return value of the mark_uninitialized instruction.
The kind of mark_uninitialized instruction specifies the type of data the mark_uninitialized instruction refers to:
var
: designates the start of a normal variable live rangerootself
: designatesself
in a struct, enum, or root classcrossmodulerootself
: same asrootself
, but in a case where it's not- really safe to treat
self
as a root because the original module might add more stored properties. This is only used for Swift 4 compatibility.
derivedself
: designatesself
in a derived (non-root) classderivedselfonly
: designatesself
in a derived (non-root) class whose stored properties have already been initializeddelegatingself
: designatesself
on a struct, enum, or class in a delegating constructor (one that calls self.init)delegatingselfallocated
: designatesself
on a class convenience initializer's initializing entry point
The purpose of the mark_uninitialized
instruction is to enable
definitive initialization analysis for global variables (when marked as
'globalvar') and instance variables (when marked as 'rootinit'), which need to
be distinguished from simple allocations.
It is produced by SILGen, and is only valid in Raw SIL. It is rewritten as appropriate by the definitive initialization pass.
sil-instruction ::= 'mark_function_escape' sil-operand (',' sil-operand)
%2 = mark_function_escape %1 : $*T
Indicates that a function definition closes over a symbolic memory location. This instruction is variadic, and all of its operands must be addresses.
The purpose of the mark_function_escape
instruction is to enable
definitive initialization analysis for global variables and instance variables,
which are not represented as box allocations.
It is produced by SILGen, and is only valid in Raw SIL. It is rewritten as appropriate by the definitive initialization pass.
init-case ::= sil-value sil-apply-substitution-list? '(' sil-value ')' ':' sil-type
set-case ::= sil-value sil-apply-substitution-list? '(' sil-value ')' ':' sil-type
sil-instruction ::= 'mark_uninitialized_behavior' init-case set-case
mark_uninitialized_behavior %init<Subs>(%storage) : $T -> U,
%set<Subs>(%self) : $V -> W
Indicates that a logical property is uninitialized at this point and needs to be
initialized by the end of the function and before any escape point for this
instruction. Assignments to the property trigger the behavior's init
or
set
logic based on the logical initialization state of the property.
It is expected that the init-case
is passed some sort of storage and the
set
case is passed self
.
This is only valid in Raw SIL.
sil-instruction ::= 'copy_addr' '[take]'? sil-value
'to' '[initialization]'? sil-operand
copy_addr [take] %0 to [initialization] %1 : $*T
// %0 and %1 must be of the same $*T address type
Loads the value at address %0
from memory and assigns a copy of it back into
memory at address %1
. A bare copy_addr
instruction when T
is a
non-trivial type:
copy_addr %0 to %1 : $*T
is equivalent to:
%new = load %0 : $*T // Load the new value from the source
%old = load %1 : $*T // Load the old value from the destination
strong_retain %new : $T // Retain the new value
strong_release %old : $T // Release the old
store %new to %1 : $*T // Store the new value to the destination
except that copy_addr
may be used even if %0
is of an address-only
type. The copy_addr
may be given one or both of the [take]
or
[initialization]
attributes:
[take]
destroys the value at the source address in the course of the copy.[initialization]
indicates that the destination address is uninitialized. Without the attribute, the destination address is treated as already initialized, and the existing value will be destroyed before the new value is stored.
The three attributed forms thus behave like the following loadable type operations:
// take-assignment
copy_addr [take] %0 to %1 : $*T
// is equivalent to:
%new = load %0 : $*T
%old = load %1 : $*T
// no retain of %new!
strong_release %old : $T
store %new to %1 : $*T
// copy-initialization
copy_addr %0 to [initialization] %1 : $*T
// is equivalent to:
%new = load %0 : $*T
strong_retain %new : $T
// no load/release of %old!
store %new to %1 : $*T
// take-initialization
copy_addr [take] %0 to [initialization] %1 : $*T
// is equivalent to:
%new = load %0 : $*T
// no retain of %new!
// no load/release of %old!
store %new to %1 : $*T
If T
is a trivial type, then copy_addr
is always equivalent to its
take-initialization form.
sil-instruction ::= 'destroy_addr' sil-operand
destroy_addr %0 : $*T
// %0 must be of an address $*T type
Destroys the value in memory at address %0
. If T
is a non-trivial type,
This is equivalent to:
%1 = load %0
strong_release %1
except that destroy_addr
may be used even if %0
is of an
address-only type. This does not deallocate memory; it only destroys the
pointed-to value, leaving the memory uninitialized.
If T
is a trivial type, then destroy_addr
is a no-op.
sil-instruction ::= 'index_addr' sil-operand ',' sil-operand
%2 = index_addr %0 : $*T, %1 : $Builtin.Int<n>
// %0 must be of an address type $*T
// %1 must be of a builtin integer type
// %2 will be of type $*T
Given an address that references into an array of values, returns the address
of the %1
-th element relative to %0
. The address must reference into
a contiguous array. It is undefined to try to reference offsets within a
non-array value, such as fields within a homogeneous struct or tuple type, or
bytes within a value, using index_addr
. (Int8
address types have no
special behavior in this regard, unlike char*
or void*
in C.) It is
also undefined behavior to index out of bounds of an array, except to index
the "past-the-end" address of the array.
sil-instruction ::= 'tail_addr' sil-operand ',' sil-operand ',' sil-type
%2 = tail_addr %0 : $*T, %1 : $Builtin.Int<n>, $E
// %0 must be of an address type $*T
// %1 must be of a builtin integer type
// %2 will be of type $*E
Given an address of an array of %1
values, returns the address of an
element which is tail-allocated after the array.
This instruction is equivalent to index_addr
except that the resulting
address is aligned-up to the tail-element type $E
.
This instruction is used to project the N-th tail-allocated array from an
object which is created by an alloc_ref
with multiple tail_elems
.
The first operand is the address of an element of the (N-1)-th array, usually
the first element. The second operand is the number of elements until the end
of that array. The result is the address of the first element of the N-th array.
It is undefined behavior if the provided address, count and type do not match the actual layout of tail-allocated arrays of the underlying object.
sil-instruction ::= 'index_raw_pointer' sil-operand ',' sil-operand
%2 = index_raw_pointer %0 : $Builtin.RawPointer, %1 : $Builtin.Int<n>
// %0 must be of $Builtin.RawPointer type
// %1 must be of a builtin integer type
// %2 will be of type $Builtin.RawPointer
Given a Builtin.RawPointer
value %0
, returns a pointer value at the
byte offset %1
relative to %0
.
sil-instruction ::= 'bind_memory' sil-operand ',' sil-operand 'to' sil-type
bind_memory %0 : $Builtin.RawPointer, %1 : $Builtin.Word to $T
// %0 must be of $Builtin.RawPointer type
// %1 must be of $Builtin.Word type
Binds memory at Builtin.RawPointer
value %0
to type $T
with enough
capacity to hold %1
values. See SE-0107: UnsafeRawPointer.
sil-instruction ::= 'begin_access' '[' sil-access ']' '[' sil-enforcement ']' '[no_nested_conflict]'? '[builtin]'? sil-operand ':' sil-type
sil-access ::= init
sil-access ::= read
sil-access ::= modify
sil-access ::= deinit
sil-enforcement ::= unknown
sil-enforcement ::= static
sil-enforcement ::= dynamic
sil-enforcement ::= unsafe
%1 = begin_access [read] [unknown] %0 : $*T
// %0 must be of $*T type.
Begins an access to the target memory.
The operand must be a root address derivation:
- a function argument,
- an
alloc_stack
instruction, - a
project_box
instruction, - a
global_addr
instruction, - a
ref_element_addr
instruction, or - another
begin_access
instruction.
It will eventually become a basic structural rule of SIL that no memory
access instructions can be directly applied to the result of one of these
instructions; they can only be applied to the result of a begin_access
on them. For now, this rule will be conditional based on compiler settings
and the SIL stage.
An access is ended with a corresponding end_access
. Accesses must be
uniquely ended on every control flow path which leads to either a function
exit or back to the begin_access
instruction. The set of active
accesses must be the same on every edge into a basic block.
An init
access takes uninitialized memory and initializes it.
It must always use static
enforcement.
An deinit
access takes initialized memory and leaves it uninitialized.
It must always use static
enforcement.
read
and modify
accesses take initialized memory and leave it
initialized. They may use unknown
enforcement only in the raw
SIL stage.
A no_nested_conflict
access has no potentially conflicting access within
its scope (on any control flow path between it and its corresponding
end_access
). Consequently, the access will not need to be tracked by the
runtime for the duration of its scope. This access may still conflict with an
outer access scope; therefore may still require dynamic enforcement at a single
point.
A builtin
access was emitted for a user-controlled Builtin (e.g. the
standard library's KeyPath access). Non-builtin accesses are auto-generated by
the compiler to enforce formal access that derives from the language. A
builtin
access is always fully enforced regardless of the compilation mode
because it may be used to enforce access outside of the current module.
sil-instruction ::= 'end_access' ( '[' 'abort' ']' )? sil-operand
Ends an access. The operand must be a begin_access
instruction.
If the begin_access
is init
or deinit
, the end_access
may be an abort
, indicating that the described transition did not
in fact take place.
sil-instruction ::= 'begin_unpaired_access' '[' sil-access ']' '[' sil-enforcement ']' '[no_nested_conflict]'? '[builtin]'? sil-operand : sil-type, sil-operand : $*Builtin.UnsafeValueBuffer
sil-access ::= init
sil-access ::= read
sil-access ::= modify
sil-access ::= deinit
sil-enforcement ::= unknown
sil-enforcement ::= static
sil-enforcement ::= dynamic
sil-enforcement ::= unsafe
%2 = begin_unpaired_access [read] [dynamic] %0 : $*T, %1 : $*Builtin.UnsafeValueBuffer
// %0 must be of $*T type.
Begins an access to the target memory. This has the same semantics and obeys all
the same constraints as begin_access
. With the following exceptions:
begin_unpaired_access
has an additional operand for the scratch buffer used to uniquely identify this access within its scope.- An access initiated by
begin_unpaired_access
must end withend_unpaired_access
unless it has theno_nested_conflict
flag. Abegin_unpaired_access
withno_nested_conflict
is effectively an instantaneous access with no associated scope. - The associated
end_unpaired_access
must use the same scratch buffer.
sil-instruction ::= 'end_unpaired_access' ( '[' 'abort' ']' )? '[' sil-enforcement ']' sil-operand : $*Builtin.UnsafeValueBuffer
sil-enforcement ::= unknown
sil-enforcement ::= static
sil-enforcement ::= dynamic
sil-enforcement ::= unsafe
%1 = end_unpaired_access [dynamic] %0 : $*Builtin.UnsafeValueBuffer
Ends an access. This has the same semantics and constraints as end_access
with the following exceptions:
- The single operand refers to the scratch buffer that uniquely identified the access with this scope.
- The enforcement level is reiterated, since the corresponding
begin_unpaired_access
may not be statically discoverable. It must be identical to thebegin_unpaired_access
enforcement.
These instructions handle reference counting of heap objects. Values of strong reference type have ownership semantics for the referenced heap object. Retain and release operations, however, are never implicit in SIL and always must be explicitly performed where needed. Retains and releases on the value may be freely moved, and balancing retains and releases may be deleted, so long as an owning retain count is maintained for the uses of the value.
All reference-counting operations are defined to work correctly on null references (whether strong, unowned, or weak). A non-null reference must actually refer to a valid object of the indicated type (or a subtype). Address operands are required to be valid and non-null.
While SIL makes reference-counting operations explicit, the SIL type system also fully represents strength of reference. This is useful for several reasons:
- Type-safety: it is impossible to erroneously emit SIL that naively
uses a
@weak
or@unowned
reference as if it were a strong reference. - Consistency: when a reference is kept in memory, instructions like
copy_addr
anddestroy_addr
implicitly carry the right semantics in the type of the address, rather than needing special variants or flags. - Ease of tooling: SIL directly stores the user's intended strength of reference, making it straightforward to generate instrumentation that would convey this to a memory profiler. In principle, with only a modest number of additions and restrictions on SIL, it would even be possible to drop all reference-counting instructions and use the type information to feed a garbage collector.
sil-instruction ::= 'strong_retain' sil-operand
strong_retain %0 : $T
// $T must be a reference type
Increases the strong retain count of the heap object referenced by %0
.
strong_release %0 : $T
// $T must be a reference type.
Decrements the strong reference count of the heap object referenced by %0
.
If the release operation brings the strong reference count of the object to
zero, the object is destroyed and @weak
references are cleared. When both
its strong and unowned reference counts reach zero, the object's memory is
deallocated.
set_deallocating %0 : $T
// $T must be a reference type.
Explicitly sets the state of the object referenced by %0
to deallocated.
This is the same operation what's done by a strong_release immediately before
it calls the deallocator of the object.
It is expected that the strong reference count of the object is one. Furthermore, no other thread may increment the strong reference count during execution of this instruction.
sil-instruction ::= 'strong_retain_unowned' sil-operand
strong_retain_unowned %0 : $@unowned T
// $T must be a reference type
Asserts that the strong reference count of the heap object referenced by %0
is still positive, then increases it by one.
sil-instruction ::= 'unowned_retain' sil-operand
unowned_retain %0 : $@unowned T
// $T must be a reference type
Increments the unowned reference count of the heap object underlying %0
.
sil-instruction ::= 'unowned_release' sil-operand
unowned_release %0 : $@unowned T
// $T must be a reference type
Decrements the unowned reference count of the heap object referenced by
%0
. When both its strong and unowned reference counts reach zero,
the object's memory is deallocated.
sil-instruction ::= 'load_weak' '[take]'? sil-operand
load_weak [take] %0 : $*@sil_weak Optional<T>
// $T must be an optional wrapping a reference type
Increments the strong reference count of the heap object held in the operand,
which must be an initialized weak reference. The result is value of type
$Optional<T>
, except that it is null
if the heap object has begun
deallocation.
If [take]
is specified then the underlying weak reference is invalidated
implying that the weak reference count of the loaded value is decremented. If
[take]
is not specified then the underlying weak reference count is not
affected by this operation (i.e. it is a +0 weak ref count operation). In either
case, the strong reference count will be incremented before any changes to the
weak reference count.
This operation must be atomic with respect to the final strong_release
on
the operand heap object. It need not be atomic with respect to store_weak
operations on the same address.
sil-instruction ::= 'store_weak' sil-value 'to' '[initialization]'? sil-operand
store_weak %0 to [initialization] %1 : $*@sil_weak Optional<T>
// $T must be an optional wrapping a reference type
Initializes or reassigns a weak reference. The operand may be nil
.
If [initialization]
is given, the weak reference must currently either be
uninitialized or destroyed. If it is not given, the weak reference must
currently be initialized. After the evaluation:
- The value that was originally referenced by the weak reference will have its weak reference count decremented by 1.
- If the optionally typed operand is non-nil, the strong reference wrapped in the optional has its weak reference count incremented by 1. In contrast, the reference's strong reference count is not touched.
This operation must be atomic with respect to the final strong_release
on
the operand (source) heap object. It need not be atomic with respect to
store_weak
or load_weak
operations on the same address.
TODO: Fill this in
TODO: Fill this in
sil-instruction :: 'fix_lifetime' sil-operand
fix_lifetime %0 : $T
// Fix the lifetime of a value %0
fix_lifetime %1 : $*T
// Fix the lifetime of the memory object referenced by %1
Acts as a use of a value operand, or of the value in memory referenced by an
address operand. Optimizations may not move operations that would destroy the
value, such as release_value
, strong_release
, copy_addr [take]
, or
destroy_addr
, past this instruction.
sil-instruction :: 'mark_dependence' sil-operand 'on' sil-operand
%2 = mark_dependence %0 : $*T on %1 : $Builtin.NativeObject
Indicates that the validity of the first operand depends on the value
of the second operand. Operations that would destroy the second value
must not be moved before any instructions which depend on the result
of this instruction, exactly as if the address had been obviously
derived from that operand (e.g. using ref_element_addr
).
The result is always equal to the first operand. The first operand will typically be an address, but it could be an address in a non-obvious form, such as a Builtin.RawPointer or a struct containing the same. Transformations should be somewhat forgiving here.
The second operand may have either object or address type. In the latter case, the dependency is on the current value stored in the address.
sil-instruction ::= 'is_unique' sil-operand
%1 = is_unique %0 : $*T
// $T must be a reference-counted type
// %1 will be of type Builtin.Int1
Checks whether %0 is the address of a unique reference to a memory object. Returns 1 if the strong reference count is 1, and 0 if the strong reference count is greater than 1.
A discussion of the semantics can be found here: :ref:`arcopts.is_unique`.
sil-instruction ::= 'is_escaping_closure' sil-operand
%1 = is_escaping_closure %0 : $@callee_guaranteed () -> ()
// %0 must be an escaping swift closure.
// %1 will be of type Builtin.Int1
Checks whether the context reference is not nil and bigger than one and returns true if it is.
sil-instruction :: 'copy_block' sil-operand
%1 = copy_block %0 : $@convention(block) T -> U
Performs a copy of an Objective-C block. Unlike retains of other reference-counted types, this can produce a different value from the operand if the block is copied from the stack to the heap.
sil-instruction :: 'copy_block_without_escaping' sil-operand 'withoutEscaping' sil-operand
%1 = copy_block %0 : $@convention(block) T -> U withoutEscaping %1 : $T -> U
Performs a copy of an Objective-C block. Unlike retains of other reference-counted types, this can produce a different value from the operand if the block is copied from the stack to the heap.
Additionally, consumes the withoutEscaping
operand %1
which is the
closure sentinel. SILGen emits these instructions when it passes @noescape
swift closures to Objective C. A mandatory SIL pass will lower this instruction
into a copy_block
and a is_escaping
/cond_fail
/destroy_value
at
the end of the lifetime of the objective c closure parameter to check whether
the sentinel closure was escaped.
sil-instruction := 'builtin' '"unsafeGuaranteed"' '<' sil-type '>' '(' sil-operand')' ':' sil-type
%1 = builtin "unsafeGuaranteed"<T>(%0 : $T) : ($T, Builtin.Int1)
// $T must be of AnyObject type.
Asserts that there exists another reference of the value %0
for the scope
delineated by the call of this builtin up to the first call of a builtin
"unsafeGuaranteedEnd"
instruction that uses the second element %1.1
of the
returned value. If no such instruction can be found nothing can be assumed. This
assertion holds for uses of the first tuple element of the returned value
%1.0
within this scope. The returned reference value equals the input
%0
.
sil-instruction := 'builtin' '"unsafeGuaranteedEnd"' '(' sil-operand')'
%1 = builtin "unsafeGuaranteedEnd"(%0 : $Builtin.Int1)
// $T must be of AnyObject type.
Ends the scope for the builtin "unsafeGuaranteed"
instruction.
These instructions bind SIL values to literal constants or to global entities.
sil-instruction ::= 'function_ref' sil-function-name ':' sil-type
%1 = function_ref @function : $@convention(thin) T -> U
// $@convention(thin) T -> U must be a thin function type
// %1 has type $T -> U
Creates a reference to a SIL function.
sil-instruction ::= 'dynamic_function_ref' sil-function-name ':' sil-type
%1 = dynamic_function_ref @function : $@convention(thin) T -> U
// $@convention(thin) T -> U must be a thin function type
// %1 has type $T -> U
Creates a reference to a dynamically_replacable SIL function. A dynamically_replacable SIL function can be replaced at runtime.
For the following Swift code:
dynamic func test_dynamically_replaceable() {}
func test_dynamic_call() {
test_dynamically_replaceable()
}
We will generate:
sil [dynamically_replacable] @test_dynamically_replaceable : $@convention(thin) () -> () {
bb0:
%0 = tuple ()
return %0 : $()
}
sil @test_dynamic_call : $@convention(thin) () -> () {
bb0:
%0 = dynamic_function_ref @test_dynamically_replaceable : $@convention(thin) () -> ()
%1 = apply %0() : $@convention(thin) () -> ()
%2 = tuple ()
return %2 : $()
}
sil-instruction ::= 'prev_dynamic_function_ref' sil-function-name ':' sil-type
%1 = prev_dynamic_function_ref @function : $@convention(thin) T -> U
// $@convention(thin) T -> U must be a thin function type
// %1 has type $T -> U
Creates a reference to a previous implemenation of a dynamic_replacement SIL function.
For the following Swift code:
@_dynamicReplacement(for: test_dynamically_replaceable())
func test_replacement() {
test_dynamically_replaceable() // calls previous implementation
}
We will generate:
sil [dynamic_replacement_for "test_dynamically_replaceable"] @test_replacement : $@convention(thin) () -> () {
bb0:
%0 = prev_dynamic_function_ref @test_replacement : $@convention(thin) () -> ()
%1 = apply %0() : $@convention(thin) () -> ()
%2 = tuple ()
return %2 : $()
}
sil-instruction ::= 'global_addr' sil-global-name ':' sil-type
%1 = global_addr @foo : $*Builtin.Word
Creates a reference to the address of a global variable which has been
previously initialized by alloc_global
. It is undefined behavior to
perform this operation on a global variable which has not been
initialized, except the global variable has a static initializer.
sil-instruction ::= 'global_value' sil-global-name ':' sil-type
%1 = global_value @v : $T
Returns the value of a global variable which has been previously initialized
by alloc_global
. It is undefined behavior to perform this operation on a
global variable which has not been initialized, except the global variable
has a static initializer.
sil-instruction ::= 'integer_literal' sil-type ',' int-literal
%1 = integer_literal $Builtin.Int<n>, 123
// $Builtin.Int<n> must be a builtin integer type
// %1 has type $Builtin.Int<n>
Creates an integer literal value. The result will be of type
Builtin.Int<n>
, which must be a builtin integer type. The literal value
is specified using Swift's integer literal syntax.
sil-instruction ::= 'float_literal' sil-type ',' int-literal
%1 = float_literal $Builtin.FP<n>, 0x3F800000
// $Builtin.FP<n> must be a builtin floating-point type
// %1 has type $Builtin.FP<n>
Creates a floating-point literal value. The result will be of type Builtin.FP<n>
, which must be a builtin floating-point type. The literal
value is specified as the bitwise representation of the floating point value,
using Swift's hexadecimal integer literal syntax.
sil-instruction ::= 'string_literal' encoding string-literal
encoding ::= 'utf8'
encoding ::= 'utf16'
encoding ::= 'objc_selector'
%1 = string_literal "asdf"
// %1 has type $Builtin.RawPointer
Creates a reference to a string in the global string table. The result
is a pointer to the data. The referenced string is always null-terminated. The
string literal value is specified using Swift's string
literal syntax (though \()
interpolations are not allowed). When
the encoding is objc_selector
, the string literal produces a
reference to a UTF-8-encoded Objective-C selector in the Objective-C
method name segment.
These instructions perform dynamic lookup of class and generic methods.
The class_method
and super_method
instructions must reference
Swift native methods and always use vtable dispatch.
The objc_method
and objc_super_method
instructions must reference
Objective-C methods (indicated by the foreign
marker on a method
reference, as in #NSObject.description!1.foreign
).
Note that objc_msgSend
invocations can only be used as the callee
of an apply
instruction or partial_apply
instruction. They cannot
be stored or used as apply
or partial_apply
arguments.
sil-instruction ::= 'class_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = class_method %0 : $T, #T.method!1 : $@convention(class_method) U -> V
// %0 must be of a class type or class metatype $T
// #T.method!1 must be a reference to a Swift native method of T or
// of one of its superclasses, at uncurry level == 1
// %1 will be of type $U -> V
Looks up a method based on the dynamic type of a class or class metatype instance. It is undefined behavior if the class value is null.
If the static type of the class instance is known, or the method is known to be final, then the instruction is a candidate for devirtualization optimization. A devirtualization pass can consult the module's VTables to find the SIL function that implements the method and promote the instruction to a static function_ref.
sil-instruction ::= 'objc_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = objc_method %0 : $T, #T.method!1.foreign : $@convention(objc_method) U -> V
// %0 must be of a class type or class metatype $T
// #T.method!1 must be a reference to an Objective-C method of T or
// of one of its superclasses, at uncurry level == 1
// %1 will be of type $U -> V
Performs Objective-C method dispatch using objc_msgSend()
.
Objective-C method calls are never candidates for devirtualization.
sil-instruction ::= 'super_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = super_method %0 : $T, #Super.method!1 : $@convention(thin) U -> V
// %0 must be of a non-root class type or class metatype $T
// #Super.method!1 must be a reference to a native Swift method of T's
// superclass or of one of its ancestor classes, at uncurry level >= 1
// %1 will be of type $@convention(thin) U -> V
Looks up a method in the superclass of a class or class metatype instance.
sil-instruction ::= 'super_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = super_method %0 : $T, #Super.method!1.foreign : $@convention(thin) U -> V
// %0 must be of a non-root class type or class metatype $T
// #Super.method!1.foreign must be a reference to an ObjC method of T's
// superclass or of one of its ancestor classes, at uncurry level >= 1
// %1 will be of type $@convention(thin) U -> V
This instruction performs an Objective-C message send using
objc_msgSuper()
.
sil-instruction ::= 'witness_method' sil-method-attributes?
sil-type ',' sil-decl-ref ':' sil-type
%1 = witness_method $T, #Proto.method!1 \
: $@convention(witness_method) <Self: Proto> U -> V
// $T must be an archetype
// #Proto.method!1 must be a reference to a method of one of the protocol
// constraints on T
// <Self: Proto> U -> V must be the type of the referenced method,
// generic on Self
// %1 will be of type $@convention(thin) <Self: Proto> U -> V
Looks up the implementation of a protocol method for a generic type variable
constrained by that protocol. The result will be generic on the Self
archetype of the original protocol and have the witness_method
calling
convention. If the referenced protocol is an @objc
protocol, the
resulting type has the objc
calling convention.
These instructions call functions or wrap them in partial application or specialization thunks.
sil-instruction ::= 'apply' '[nothrow]'? sil-value
sil-apply-substitution-list?
'(' (sil-value (',' sil-value)*)? ')'
':' sil-type
sil-apply-substitution-list ::= '<' sil-substitution
(',' sil-substitution)* '>'
sil-substitution ::= type '=' type
%r = apply %0(%1, %2, ...) : $(A, B, ...) -> R
// Note that the type of the callee '%0' is specified *after* the arguments
// %0 must be of a concrete function type $(A, B, ...) -> R
// %1, %2, etc. must be of the argument types $A, $B, etc.
// %r will be of the return type $R
%r = apply %0<A, B>(%1, %2, ...) : $<T, U>(T, U, ...) -> R
// %0 must be of a polymorphic function type $<T, U>(T, U, ...) -> R
// %1, %2, etc. must be of the argument types after substitution $A, $B, etc.
// %r will be of the substituted return type $R'
Transfers control to function %0
, passing it the given arguments. In
the instruction syntax, the type of the callee is specified after the argument
list; the types of the argument and of the defined value are derived from the
function type of the callee. The input argument tuple type is destructured,
and each element is passed as an individual argument. The apply
instruction does no retaining or releasing of its arguments by itself; the
calling convention's retain/release policy must be handled by separate
explicit retain
and release
instructions. The return value will
likewise not be implicitly retained or released.
The callee value must have function type. That function type may not
have an error result, except the instruction has the nothrow
attribute set.
The nothrow
attribute specifies that the callee has an error result but
does not actually throw.
For the regular case of calling a function with error result, use try_apply
.
NB: If the callee value is of a thick function type, apply
currently
consumes the callee value at +1 strong retain count.
If the callee is generic, all of its generic parameters must be bound by the given substitution list. The arguments and return value is given with these generic substitutions applied.
sil-instruction ::= 'begin_apply' '[nothrow]'? sil-value
sil-apply-substitution-list?
'(' (sil-value (',' sil-value)*)? ')'
':' sil-type
(%anyAddr, %float, %token) = begin_apply %0() : $@yield_once () -> (@yields @inout %Any, @yields Float)
// %anyAddr : $*Any
// %float : $Float
// %token is a token
Transfers control to coroutine %0
, passing it the given arguments.
The rules for the application generally follow the rules for apply
,
except:
- the callee value must have a
yield_once
coroutine type, - control returns to this function not when the coroutine performs a
return
, but when it performs ayield
, and - the instruction results are derived from the yields of the coroutine instead of its normal results.
The final result of a begin_apply
is a "token", a special value which
can only be used as the operand of an end_apply
or abort_apply
instruction. Before this second instruction is executed, the coroutine
is said to be "suspended", and the token represents a reference to its
suspended activation record.
The other results of the instruction correspond to the yields in the
coroutine type. In general, the rules of a yield are similar to the rules
for a parameter, interpreted as if the coroutine caller (the one
executing the begin_apply
) were being "called" by the yield
:
- If a yield has an indirect convention, the corresponding result will
have an address type; otherwise it has an object type. For example,
a result corresponding to an
@in Any
yield will have type$Any
. - The convention attributes are the same as the parameter convention
attributes, interpreted as if the
yield
were the "call" and thebegin_apply
marked the entry to the "callee". For example, an@in Any
yield transfers ownership of theAny
value reference from the coroutine to the caller, which must destroy or move the value from that position before ending or aborting the coroutine.
A begin_apply
must be uniquely either ended or aborted before
exiting the function or looping to an earlier portion of the function.
When throwing coroutines are supported, there will need to be a
try_begin_apply
instruction.
sil-instruction ::= 'abort_apply' sil-value
abort_apply %token
Aborts the given coroutine activation, which is currently suspended at
a yield
instruction. Transfers control to the coroutine and takes
the unwind
path from the yield
. Control is transferred back
when the coroutine reaches an unwind
instruction.
The operand must always be the token result of a begin_apply
instruction, which is why it need not specify a type.
Throwing coroutines will not require a new instruction for aborting a coroutine; a coroutine is not allowed to throw when it is being aborted.
sil-instruction ::= 'end_apply' sil-value
end_apply %token
Ends the given coroutine activation, which is currently suspended at
a yield
instruction. Transfers control to the coroutine and takes
the resume
path from the yield
. Control is transferred back
when the coroutine reaches a return
instruction.
The operand must always be the token result of a begin_apply
instruction, which is why it need not specify a type.
end_apply
currently has no instruction results. If coroutines were
allowed to have normal results, they would be producted by end_apply
.
When throwing coroutines are supported, there will need to be a
try_end_apply
instruction.
sil-instruction ::= 'partial_apply' callee-ownership-attr? on-stack-attr? sil-value
sil-apply-substitution-list?
'(' (sil-value (',' sil-value)*)? ')'
':' sil-type
callee-ownership-attr ::= '[callee_guaranteed]'
on-stack-attr ::= '[on_stack]'
%c = partial_apply %0(%1, %2, ...) : $(Z..., A, B, ...) -> R
// Note that the type of the callee '%0' is specified *after* the arguments
// %0 must be of a concrete function type $(Z..., A, B, ...) -> R
// %1, %2, etc. must be of the argument types $A, $B, etc.,
// of the tail part of the argument tuple of %0
// %c will be of the partially-applied thick function type (Z...) -> R
%c = partial_apply %0<A, B>(%1, %2, ...) : $(Z..., T, U, ...) -> R
// %0 must be of a polymorphic function type $<T, U>(T, U, ...) -> R
// %1, %2, etc. must be of the argument types after substitution $A, $B, etc.
// of the tail part of the argument tuple of %0
// %r will be of the substituted thick function type $(Z'...) -> R'
Creates a closure by partially applying the function %0
to a partial
sequence of its arguments. In the instruction syntax, the type of the callee is
specified after the argument list; the types of the argument and of the defined
value are derived from the function type of the callee. If the partial_apply
has an escaping function type (not [on_stack]
) the closure context will be
allocated with retain count 1 and initialized to contain the values %1
,
%2
, etc. The closed-over values will not be retained; that must be done
separately before the partial_apply
. The closure does however take ownership
of the partially applied arguments; when the closure reference count reaches
zero, the contained values will be destroyed. If the partial_apply
has a
@noescape
function type (partial_apply [on_stack]
) the closure context
is allocated on the stack and initialized to contain the closed-over values. The
closed-over values are not retained, lifetime of the closed-over values must be
managed separately. The lifetime of the stack context of a partial_apply
[on_stack]
must be terminated with a dealloc_stack
.
If the callee is generic, all of its generic parameters must be bound by the given substitution list. The arguments are given with these generic substitutions applied, and the resulting closure is of concrete function type with the given substitutions applied. The generic parameters themselves cannot be partially applied; all of them must be bound. The result is always a concrete function.
TODO: The instruction, when applied to a generic function, currently implicitly performs abstraction difference transformations enabled by the given substitutions, such as promoting address-only arguments and returns to register arguments. This should be fixed.
By default, partial_apply
creates a closure whose invocation takes ownership
of the context, meaning that a call implicitly releases the closure. The
[callee_guaranteed]
change this to a caller-guaranteed model, where the
caller promises not to release the closure while the function is being called.
This instruction is used to implement both curry thunks and closures. A curried function in Swift:
func foo(_ a:A)(b:B)(c:C)(d:D) -> E { /* body of foo */ }
emits curry thunks in SIL as follows (retains and releases omitted for clarity):
func @foo : $@convention(thin) A -> B -> C -> D -> E {
entry(%a : $A):
%foo_1 = function_ref @foo_1 : $@convention(thin) (B, A) -> C -> D -> E
%thunk = partial_apply %foo_1(%a) : $@convention(thin) (B, A) -> C -> D -> E
return %thunk : $B -> C -> D -> E
}
func @foo_1 : $@convention(thin) (B, A) -> C -> D -> E {
entry(%b : $B, %a : $A):
%foo_2 = function_ref @foo_2 : $@convention(thin) (C, B, A) -> D -> E
%thunk = partial_apply %foo_2(%b, %a) \
: $@convention(thin) (C, B, A) -> D -> E
return %thunk : $(B, A) -> C -> D -> E
}
func @foo_2 : $@convention(thin) (C, B, A) -> D -> E {
entry(%c : $C, %b : $B, %a : $A):
%foo_3 = function_ref @foo_3 : $@convention(thin) (D, C, B, A) -> E
%thunk = partial_apply %foo_3(%c, %b, %a) \
: $@convention(thin) (D, C, B, A) -> E
return %thunk : $(C, B, A) -> D -> E
}
func @foo_3 : $@convention(thin) (D, C, B, A) -> E {
entry(%d : $D, %c : $C, %b : $B, %a : $A):
// ... body of foo ...
}
A local function in Swift that captures context, such as bar
in the
following example:
func foo(_ x:Int) -> Int {
func bar(_ y:Int) -> Int {
return x + y
}
return bar(1)
}
lowers to an uncurried entry point and is curried in the enclosing function:
func @bar : $@convention(thin) (Int, @box Int, *Int) -> Int {
entry(%y : $Int, %x_box : $@box Int, %x_address : $*Int):
// ... body of bar ...
}
func @foo : $@convention(thin) Int -> Int {
entry(%x : $Int):
// Create a box for the 'x' variable
%x_box = alloc_box $Int
%x_addr = project_box %x_box : $@box Int
store %x to %x_addr : $*Int
// Create the bar closure
%bar_uncurried = function_ref @bar : $(Int, Int) -> Int
%bar = partial_apply %bar_uncurried(%x_box, %x_addr) \
: $(Int, Builtin.NativeObject, *Int) -> Int
// Apply it
%1 = integer_literal $Int, 1
%ret = apply %bar(%1) : $(Int) -> Int
// Clean up
release %bar : $(Int) -> Int
return %ret : $Int
}
sil-instruction ::= 'builtin' string-literal
sil-apply-substitution-list?
'(' (sil-operand (',' sil-operand)*)? ')'
':' sil-type
%1 = builtin "foo"(%1 : $T, %2 : $U) : $V
// "foo" must name a function in the Builtin module
Invokes functionality built into the backend code generator, such as LLVM- level instructions and intrinsics.
These instructions access metatypes, either statically by type name or dynamically by introspecting class or generic values.
sil-instruction ::= 'metatype' sil-type
%1 = metatype $T.Type
// %1 has type $T.Type
Creates a reference to the metatype object for type T
.
sil-instruction ::= 'value_metatype' sil-type ',' sil-operand
%1 = value_metatype $T.Type, %0 : $T
// %0 must be a value or address of type $T
// %1 will be of type $T.Type
Obtains a reference to the dynamic metatype of the value %0
.
sil-instruction ::= 'existential_metatype' sil-type ',' sil-operand
%1 = existential_metatype $P.Type, %0 : $P
// %0 must be a value of class protocol or protocol composition
// type $P, or an address of address-only protocol type $*P
// %1 will be a $P.Type value referencing the metatype of the
// concrete value inside %0
Obtains the metatype of the concrete value
referenced by the existential container referenced by %0
.
sil-instruction ::= 'objc_protocol' protocol-decl : sil-type
%0 = objc_protocol #ObjCProto : $Protocol
TODO Fill this in.
These instructions construct and project elements from structs, tuples, and class instances.
sil-instruction ::= 'retain_value' sil-operand
retain_value %0 : $A
Retains a loadable value, which simply retains any references it holds.
For trivial types, this is a no-op. For reference types, this is equivalent to
a strong_retain
. For @unowned
types, this is equivalent to an
unowned_retain
. In each of these cases, those are the preferred forms.
For aggregate types, especially enums, it is typically both easier and more efficient to reason about aggregate copies than it is to reason about copies of the subobjects.
sil-instruction ::= 'retain_value_addr' sil-operand
retain_value_addr %0 : $*A
Retains a loadable value inside given address, which simply retains any references it holds.
sil-instruction ::= 'unmanaged_retain_value' sil-value
unmanaged_retain_value %0 : $A
This instruction has the same local semantics as retain_value
but:
- Is valid in ownership qualified SIL.
- Is not intended to be statically paired at compile time by the compiler.
The intention is that this instruction is used to implement unmanaged constructs.
sil-instruction ::= 'copy_value' sil-operand
%1 = copy_value %0 : $A
Performs a copy of a loadable value as if by the value's type lowering and returns the copy. The returned copy semantically is a value that is completely independent of the operand. In terms of specific types:
- For trivial types, this is equivalent to just propagating through the trivial value.
- For reference types, this is equivalent to performing a
strong_retain
operation and returning the reference. - For
@unowned
types, this is equivalent to performing anunowned_retain
and returning the operand. - For aggregate types, this is equivalent to recursively performing a
copy_value
on its components, forming a new aggregate from the copied components, and then returning the new aggregate.
In ownership qualified functions, a copy_value
produces a +1 value that must
be consumed at most once along any path through the program.
sil-instruction ::= 'release_value' sil-operand
release_value %0 : $A
Destroys a loadable value, by releasing any retainable pointers within it.
This is defined to be equivalent to storing the operand into a stack allocation and using 'destroy_addr' to destroy the object there.
For trivial types, this is a no-op. For reference types, this is
equivalent to a strong_release
. For @unowned
types, this is
equivalent to an unowned_release
. In each of these cases, those
are the preferred forms.
For aggregate types, especially enums, it is typically both easier and more efficient to reason about aggregate destroys than it is to reason about destroys of the subobjects.
sil-instruction ::= 'release_value_addr' sil-operand
release_value_addr %0 : $*A
Destroys a loadable value inside given address, by releasing any retainable pointers within it.
sil-instruction ::= 'unmanaged_release_value' sil-value
unmanaged_release_value %0 : $A
This instruction has the same local semantics as release_value
but:
- Is valid in ownership qualified SIL.
- Is not intended to be statically paired at compile time by the compiler.
The intention is that this instruction is used to implement unmanaged constructs.
sil-instruction ::= 'destroy_value' sil-operand
destroy_value %0 : $A
Destroys a loadable value, by releasing any retainable pointers within it.
This is defined to be equivalent to storing the operand into a stack allocation and using 'destroy_addr' to destroy the object there.
For trivial types, this is a no-op. For reference types, this is
equivalent to a strong_release
. For @unowned
types, this is
equivalent to an unowned_release
. In each of these cases, those
are the preferred forms.
For aggregate types, especially enums, it is typically both easier and more efficient to reason about aggregate destroys than it is to reason about destroys of the subobjects.
sil-instruction ::= 'autorelease_value' sil-operand
autorelease_value %0 : $A
TODO Complete this section.
sil-instruction ::= 'tuple' sil-tuple-elements
sil-tuple-elements ::= '(' (sil-operand (',' sil-operand)*)? ')'
sil-tuple-elements ::= sil-type '(' (sil-value (',' sil-value)*)? ')'
%1 = tuple (%a : $A, %b : $B, ...)
// $A, $B, etc. must be loadable non-address types
// %1 will be of the "simple" tuple type $(A, B, ...)
%1 = tuple $(a:A, b:B, ...) (%a, %b, ...)
// (a:A, b:B, ...) must be a loadable tuple type
// %1 will be of the type $(a:A, b:B, ...)
Creates a loadable tuple value by aggregating multiple loadable values.
If the destination type is a "simple" tuple type, that is, it has no keyword argument labels or variadic arguments, then the first notation can be used, which interleaves the element values and types. If keyword names or variadic fields are specified, then the second notation must be used, which spells out the tuple type before the fields.
sil-instruction ::= 'tuple_extract' sil-operand ',' int-literal
%1 = tuple_extract %0 : $(T...), 123
// %0 must be of a loadable tuple type $(T...)
// %1 will be of the type of the selected element of %0
Extracts an element from a loadable tuple value.
sil-instruction ::= 'tuple_element_addr' sil-operand ',' int-literal
%1 = tuple_element_addr %0 : $*(T...), 123
// %0 must of a $*(T...) address-of-tuple type
// %1 will be of address type $*U where U is the type of the 123rd
// element of T
Given the address of a tuple in memory, derives the address of an element within that value.
sil-instruction ::= 'destructure_tuple' sil-operand
(%elt1, ..., %eltn) = destructure_tuple %0 : $(Elt1Ty, ..., EltNTy)
// %0 must be a tuple of type $(Elt1Ty, ..., EltNTy)
// %eltN must have the type $EltNTy
Given a tuple value, split the value into its constituent elements.
sil-instruction ::= 'struct' sil-type '(' (sil-operand (',' sil-operand)*)? ')'
%1 = struct $S (%a : $A, %b : $B, ...)
// $S must be a loadable struct type
// $A, $B, ... must be the types of the physical 'var' fields of $S in order
// %1 will be of type $S
Creates a value of a loadable struct type by aggregating multiple loadable values.
sil-instruction ::= 'struct_extract' sil-operand ',' sil-decl-ref
%1 = struct_extract %0 : $S, #S.field
// %0 must be of a loadable struct type $S
// #S.field must be a physical 'var' field of $S
// %1 will be of the type of the selected field of %0
Extracts a physical field from a loadable struct value.
sil-instruction ::= 'struct_element_addr' sil-operand ',' sil-decl-ref
%1 = struct_element_addr %0 : $*S, #S.field
// %0 must be of a struct type $S
// #S.field must be a physical 'var' field of $S
// %1 will be the address of the selected field of %0
Given the address of a struct value in memory, derives the address of a physical field within the value.
sil-instruction ::= 'destructure_struct' sil-operand
(%elt1, ..., %eltn) = destructure_struct %0 : $S
// %0 must be a struct of type $S
// %eltN must have the same type as the Nth field of $S
Given a struct, split the struct into its constituent fields.
sil-instruction ::= 'object' sil-type '(' (sil-operand (',' sil-operand)*)? ')'
object $T (%a : $A, %b : $B, ...)
// $T must be a non-generic or bound generic reference type
// The first operands must match the stored properties of T
// Optionally there may be more elements, which are tail-allocated to T
Constructs a statically initialized object. This instruction can only appear as final instruction in a global variable static initializer list.
sil-instruction ::= 'ref_element_addr' sil-operand ',' sil-decl-ref
%1 = ref_element_addr %0 : $C, #C.field
// %0 must be a value of class type $C
// #C.field must be a non-static physical field of $C
// %1 will be of type $*U where U is the type of the selected field
// of C
Given an instance of a class, derives the address of a physical instance variable inside the instance. It is undefined behavior if the class value is null.
sil-instruction ::= 'ref_tail_addr' sil-operand ',' sil-type
%1 = ref_tail_addr %0 : $C, $E
// %0 must be a value of class type $C with tail-allocated elements $E
// %1 will be of type $*E
Given an instance of a class, which is created with tail-allocated array(s),
derives the address of the first element of the first tail-allocated array.
This instruction is used to project the first tail-allocated element from an
object which is created by an alloc_ref
with tail_elems
.
It is undefined behavior if the class instance does not have tail-allocated
arrays or if the element-types do not match.
These instructions construct and manipulate values of enum type. Loadable enum values are created with the enum instruction. Address-only enums require two-step initialization. First, if the case requires data, that data is stored into the enum at the address projected by init_enum_data_addr. This step is skipped for cases without data. Finally, the tag for the enum is injected with an inject_enum_addr instruction:
enum AddressOnlyEnum {
case HasData(AddressOnlyType)
case NoData
}
sil @init_with_data : $(AddressOnlyType) -> AddressOnlyEnum {
entry(%0 : $*AddressOnlyEnum, %1 : $*AddressOnlyType):
// Store the data argument for the case.
%2 = init_enum_data_addr %0 : $*AddressOnlyEnum, #AddressOnlyEnum.HasData!enumelt.1
copy_addr [take] %2 to [initialization] %1 : $*AddressOnlyType
// Inject the tag.
inject_enum_addr %0 : $*AddressOnlyEnum, #AddressOnlyEnum.HasData!enumelt.1
return
}
sil @init_without_data : $() -> AddressOnlyEnum {
// No data. We only need to inject the tag.
inject_enum_addr %0 : $*AddressOnlyEnum, #AddressOnlyEnum.NoData!enumelt
return
}
Accessing the value of a loadable enum is inseparable from dispatching on its discriminator and is done with the switch_enum terminator:
enum Foo { case A(Int), B(String) }
sil @switch_foo : $(Foo) -> () {
entry(%foo : $Foo):
switch_enum %foo : $Foo, case #Foo.A!enumelt.1: a_dest, case #Foo.B!enumelt.1: b_dest
a_dest(%a : $Int):
/* use %a */
b_dest(%b : $String):
/* use %b */
}
An address-only enum can be tested by branching on it using the switch_enum_addr terminator. Its value can then be taken by destructively projecting the enum value with unchecked_take_enum_data_addr:
enum Foo<T> { case A(T), B(String) }
sil @switch_foo : $<T> (Foo<T>) -> () {
entry(%foo : $*Foo<T>):
switch_enum_addr %foo : $*Foo<T>, case #Foo.A!enumelt.1: a_dest, \
case #Foo.B!enumelt.1: b_dest
a_dest:
%a = unchecked_take_enum_data_addr %foo : $*Foo<T>, #Foo.A!enumelt.1
/* use %a */
b_dest:
%b = unchecked_take_enum_data_addr %foo : $*Foo<T>, #Foo.B!enumelt.1
/* use %b */
}
Both switch_enum and switch_enum_addr must include a default
case
unless the enum can be exhaustively switched in the current function, i.e. when
the compiler can be sure that it knows all possible present and future values
of the enum in question. This is generally true for enums defined in Swift, but
there are two exceptions: non-frozen enums declared in libraries compiled
with the -enable-library-evolution
flag, which may grow new cases in the future in
an ABI-compatible way; and enums marked with the objc
attribute, for which
other bit patterns are permitted for compatibility with C. All enums imported
from C are treated as "non-exhaustive" for the same reason, regardless of the
presence or value of the enum_extensibility
Clang attribute.
(See SE-0192 for more information about non-frozen enums.)
sil-instruction ::= 'enum' sil-type ',' sil-decl-ref (',' sil-operand)?
%1 = enum $U, #U.EmptyCase!enumelt
%1 = enum $U, #U.DataCase!enumelt.1, %0 : $T
// $U must be an enum type
// #U.DataCase or #U.EmptyCase must be a case of enum $U
// If #U.Case has a data type $T, %0 must be a value of type $T
// If #U.Case has no data type, the operand must be omitted
// %1 will be of type $U
Creates a loadable enum value in the given case
. If the case
has a
data type, the enum value will contain the operand value.
sil-instruction ::= 'unchecked_enum_data' sil-operand ',' sil-decl-ref
%1 = unchecked_enum_data %0 : $U, #U.DataCase!enumelt.1
// $U must be an enum type
// #U.DataCase must be a case of enum $U with data
// %1 will be of object type $T for the data type of case U.DataCase
Unsafely extracts the payload data for an enum case
from an enum value.
It is undefined behavior if the enum does not contain a value of the given
case.
sil-instruction ::= 'init_enum_data_addr' sil-operand ',' sil-decl-ref
%1 = init_enum_data_addr %0 : $*U, #U.DataCase!enumelt.1
// $U must be an enum type
// #U.DataCase must be a case of enum $U with data
// %1 will be of address type $*T for the data type of case U.DataCase
Projects the address of the data for an enum case
inside an enum. This
does not modify the enum or check its value. It is intended to be used as
part of the initialization sequence for an address-only enum. Storing to
the init_enum_data_addr
for a case followed by inject_enum_addr
with that
same case is guaranteed to result in a fully-initialized enum value of that
case being stored. Loading from the init_enum_data_addr
of an initialized
enum value or injecting a mismatched case tag is undefined behavior.
The address is invalidated as soon as the operand enum is fully initialized by
an inject_enum_addr
.
sil-instruction ::= 'inject_enum_addr' sil-operand ',' sil-decl-ref
inject_enum_addr %0 : $*U, #U.Case!enumelt
// $U must be an enum type
// #U.Case must be a case of enum $U
// %0 will be overlaid with the tag for #U.Case
Initializes the enum value referenced by the given address by overlaying the
tag for the given case. If the case has no data, this instruction is sufficient
to initialize the enum value. If the case has data, the data must be stored
into the enum at the init_enum_data_addr
address for the case before
inject_enum_addr
is applied. It is undefined behavior if
inject_enum_addr
is applied for a case with data to an uninitialized enum,
or if inject_enum_addr
is applied for a case with data when data for a
mismatched case has been stored to the enum.
sil-instruction ::= 'unchecked_take_enum_data_addr' sil-operand ',' sil-decl-ref
%1 = unchecked_take_enum_data_addr %0 : $*U, #U.DataCase!enumelt.1
// $U must be an enum type
// #U.DataCase must be a case of enum $U with data
// %1 will be of address type $*T for the data type of case U.DataCase
Invalidates an enum value, and takes the address of the payload for the given
enum case
in-place in memory. The referenced enum value is no longer valid,
but the payload value referenced by the result address is valid and must be
destroyed. It is undefined behavior if the referenced enum does not contain a
value of the given case
. The result shares memory with the original enum
value; the enum memory cannot be reinitialized as an enum until the payload has
also been invalidated.
(1.0 only)
For the first payloaded case of an enum, unchecked_take_enum_data_addr
is guaranteed to have no side effects; the enum value will not be invalidated.
sil-instruction ::= 'select_enum' sil-operand sil-select-case*
(',' 'default' sil-value)?
':' sil-type
%n = select_enum %0 : $U, \
case #U.Case1!enumelt: %1, \
case #U.Case2!enumelt: %2, /* ... */ \
default %3 : $T
// $U must be an enum type
// #U.Case1, Case2, etc. must be cases of enum $U
// %1, %2, %3, etc. must have type $T
// %n has type $T
Selects one of the "case" or "default" operands based on the case of an enum value. This is equivalent to a trivial switch_enum branch sequence:
entry:
switch_enum %0 : $U, \
case #U.Case1!enumelt: bb1, \
case #U.Case2!enumelt: bb2, /* ... */ \
default bb_default
bb1:
br cont(%1 : $T) // value for #U.Case1
bb2:
br cont(%2 : $T) // value for #U.Case2
bb_default:
br cont(%3 : $T) // value for default
cont(%n : $T):
// use argument %n
but turns the control flow dependency into a data flow dependency. For address-only enums, select_enum_addr offers the same functionality for an indirectly referenced enum value in memory.
Like switch_enum, select_enum
must have a default
case unless the
enum can be exhaustively switched in the current function.
sil-instruction ::= 'select_enum_addr' sil-operand sil-select-case*
(',' 'default' sil-value)?
':' sil-type
%n = select_enum_addr %0 : $*U, \
case #U.Case1!enumelt: %1, \
case #U.Case2!enumelt: %2, /* ... */ \
default %3 : $T
// %0 must be the address of an enum type $*U
// #U.Case1, Case2, etc. must be cases of enum $U
// %1, %2, %3, etc. must have type $T
// %n has type $T
Selects one of the "case" or "default" operands based on the case of the referenced enum value. This is the address-only counterpart to select_enum.
Like switch_enum_addr, select_enum_addr
must have a default
case
unless the enum can be exhaustively switched in the current function.
These instructions create and manipulate values of protocol and protocol composition type. From SIL's perspective, protocol and protocol composition types consist of an existential container, which is a generic container for a value of unknown runtime type, referred to as an "existential type" in type theory. The existential container consists of a reference to the witness table(s) for the protocol(s) referred to by the protocol type and a reference to the underlying concrete value, which may be either stored in-line inside the existential container for small values or allocated separately into a buffer owned and managed by the existential container for larger values.
Depending on the constraints applied to an existential type, an existential container may use one of several representations:
- Opaque existential containers: If none of the protocols in a protocol
type are class protocols, then the existential container for that type is
address-only and referred to in the implementation as an opaque existential
container. The value semantics of the existential container propagate to the
contained concrete value. Applying
copy_addr
to an opaque existential container copies the contained concrete value, deallocating or reallocating the destination container's owned buffer if necessary. Applyingdestroy_addr
to an opaque existential container destroys the concrete value and deallocates any buffers owned by the existential container. The following instructions manipulate opaque existential containers: - Opaque existential containers loadable types: In the SIL Opaque Values mode of operation, we take an opaque value as-is. Said value might be replaced with one of the _addr instructions above before IR generation. The following instructions manipulate "loadable" opaque existential containers:
- Class existential containers: If a protocol type is constrained by one or
more class protocols, then the existential container for that type is
loadable and referred to in the implementation as a class existential
container. Class existential containers have reference semantics and can be
retain
-ed andrelease
-d. The following instructions manipulate class existential containers: - Metatype existential containers: Existential metatypes use a container consisting of the type metadata for the conforming type along with the protocol conformances. Metatype existential containers are trivial types. The following instructions manipulate metatype existential containers:
- Boxed existential containers: The standard library
Error
protocol uses a size-optimized reference-counted container, which indirectly stores the conforming value. Boxed existential containers can beretain
-ed andrelease
-d. The following instructions manipulate boxed existential containers:
Some existential types may additionally support specialized representations
when they contain certain known concrete types. For example, when Objective-C
interop is available, the Error
protocol existential supports
a class existential container representation for NSError
objects, so it
can be initialized from one using init_existential_ref
instead of the
more expensive alloc_existential_box
:
bb(%nserror: $NSError):
// The slow general way to form an Error, allocating a box and
// storing to its value buffer:
%error1 = alloc_existential_box $Error, $NSError
%addr = project_existential_box $NSError in %error1 : $Error
strong_retain %nserror: $NSError
store %nserror to %addr : $NSError
// The fast path supported for NSError:
strong_retain %nserror: $NSError
%error2 = init_existential_ref %nserror: $NSError, $Error
sil-instruction ::= 'init_existential_addr' sil-operand ',' sil-type
%1 = init_existential_addr %0 : $*P, $T
// %0 must be of a $*P address type for non-class protocol or protocol
// composition type P
// $T must be an AST type that fulfills protocol(s) P
// %1 will be of type $*T', where T' is the maximally abstract lowering
// of type T
Partially initializes the memory referenced by %0
with an existential
container prepared to contain a value of type $T
. The result of the
instruction is an address referencing the storage for the contained value, which
remains uninitialized. The contained value must be store
-d or
copy_addr
-ed to in order for the existential value to be fully initialized.
If the existential container needs to be destroyed while the contained value
is uninitialized, deinit_existential_addr
must be used to do so. A fully
initialized existential container can be destroyed with destroy_addr
as
usual. It is undefined behavior to destroy_addr
a partially-initialized
existential container.
sil-instruction ::= 'init_existential_value' sil-operand ':' sil-type ','
sil-type
%1 = init_existential_value %0 : $L' : $C, $P
// %0 must be of loadable type $L', lowered from AST type $L, conforming to
// protocol(s) $P
// %1 will be of type $P
Loadable version of the above: Inits-up the existential
container prepared to contain a value of type $P
.
sil-instruction ::= 'deinit_existential_addr' sil-operand
deinit_existential_addr %0 : $*P
// %0 must be of a $*P address type for non-class protocol or protocol
// composition type P
Undoes the partial initialization performed by
init_existential_addr
. deinit_existential_addr
is only valid for
existential containers that have been partially initialized by
init_existential_addr
but haven't had their contained value initialized.
A fully initialized existential must be destroyed with destroy_addr
.
sil-instruction ::= 'deinit_existential_value' sil-operand
deinit_existential_value %0 : $P
// %0 must be of a $P opaque type for non-class protocol or protocol
// composition type P
Undoes the partial initialization performed by
init_existential_value
. deinit_existential_value
is only valid for
existential containers that have been partially initialized by
init_existential_value
but haven't had their contained value initialized.
A fully initialized existential must be destroyed with destroy_value
.
sil-instruction ::= 'open_existential_addr' sil-allowed-access sil-operand 'to' sil-type
sil-allowed-access ::= 'immutable_access'
sil-allowed-access ::= 'mutable_access'
%1 = open_existential_addr immutable_access %0 : $*P to $*@opened P
// %0 must be of a $*P type for non-class protocol or protocol composition
// type P
// $*@opened P must be a unique archetype that refers to an opened
// existential type P.
// %1 will be of type $*@opened P
Obtains the address of the concrete value inside the existential
container referenced by %0
. The protocol conformances associated
with this existential container are associated directly with the
archetype $*@opened P
. This pointer can be used with any operation
on archetypes, such as witness_method
assuming this operation obeys the
access constraint: The returned address can either allow mutable_access
or
immutable_access
. Users of the returned address may only consume
(e.g destroy_addr
or copy_addr [take]
) or mutate the value at the
address if they have mutable_access
.
sil-instruction ::= 'open_existential_value' sil-operand 'to' sil-type
%1 = open_existential_value %0 : $P to $@opened P
// %0 must be of a $P type for non-class protocol or protocol composition
// type P
// $@opened P must be a unique archetype that refers to an opened
// existential type P.
// %1 will be of type $@opened P
Loadable version of the above: Opens-up the existential
container associated with %0
. The protocol conformances associated
with this existential container are associated directly with the
archetype $@opened P
.
sil-instruction ::= 'init_existential_ref' sil-operand ':' sil-type ','
sil-type
%1 = init_existential_ref %0 : $C' : $C, $P
// %0 must be of class type $C', lowered from AST type $C, conforming to
// protocol(s) $P
// $P must be a class protocol or protocol composition type
// %1 will be of type $P
Creates a class existential container of type $P
containing a reference to
the class instance %0
.
sil-instruction ::= 'open_existential_ref' sil-operand 'to' sil-type
%1 = open_existential_ref %0 : $P to $@opened P
// %0 must be of a $P type for a class protocol or protocol composition
// $@opened P must be a unique archetype that refers to an opened
// existential type P
// %1 will be of type $@opened P
Extracts the class instance reference from a class existential
container. The protocol conformances associated with this existential
container are associated directly with the archetype @opened P
. This
pointer can be used with any operation on archetypes, such as
witness_method
. When the operand is of metatype type, the result
will be the metatype of the opened archetype.
sil-instruction ::= 'init_existential_metatype' sil-operand ',' sil-type
%1 = init_existential_metatype $0 : $@<rep> T.Type, $@<rep> P.Type
// %0 must be of a metatype type $@<rep> T.Type where T: P
// %@<rep> P.Type must be the existential metatype of a protocol or protocol
// composition, with the same metatype representation <rep>
// %1 will be of type $@<rep> P.Type
Creates a metatype existential container of type $P.Type
containing the
conforming metatype of $T
.
sil-instruction ::= 'open_existential_metatype' sil-operand 'to' sil-type
%1 = open_existential_metatype %0 : $@<rep> P.Type to $@<rep> (@opened P).Type
// %0 must be of a $P.Type existential metatype for a protocol or protocol
// composition
// $@<rep> (@opened P).Type must be the metatype of a unique archetype that
// refers to an opened existential type P, with the same metatype
// representation <rep>
// %1 will be of type $@<rep> (@opened P).Type
Extracts the metatype from an existential metatype. The protocol conformances associated with this existential
container are associated directly with the archetype @opened P
.
sil-instruction ::= 'alloc_existential_box' sil-type ',' sil-type
%1 = alloc_existential_box $P, $T
// $P must be a protocol or protocol composition type with boxed
// representation
// $T must be an AST type that conforms to P
// %1 will be of type $P
// %1#1 will be of type $*T', where T' is the most abstracted lowering of T
Allocates a boxed existential container of type $P
with space to hold a
value of type $T'
. The box is not fully initialized until a valid value
has been stored into the box. If the box must be deallocated before it is
fully initialized, dealloc_existential_box
must be used. A fully
initialized box can be retain
-ed and release
-d like any
reference-counted type. The project_existential_box
instruction is used
to retrieve the address of the value inside the container.
sil-instruction ::= 'project_existential_box' sil-type 'in' sil-operand
%1 = project_existential_box $T in %0 : $P
// %0 must be a value of boxed protocol or protocol composition type $P
// $T must be the most abstracted lowering of the AST type for which the box
// was allocated
// %1 will be of type $*T
Projects the address of the value inside a boxed existential container.
The address is dependent on the lifetime of the owner reference %0
.
It is undefined behavior if the concrete type $T
is not the same type for
which the box was allocated with alloc_existential_box
.
sil-instruction ::= 'open_existential_box' sil-operand 'to' sil-type
%1 = open_existential_box %0 : $P to $*@opened P
// %0 must be a value of boxed protocol or protocol composition type $P
// %@opened P must be the address type of a unique archetype that refers to
/// an opened existential type P
// %1 will be of type $*@opened P
Projects the address of the value inside a boxed existential container, and
uses the enclosed type and protocol conformance metadata to bind the
opened archetype $@opened P
. The result address is dependent on both
the owning box and the enclosing function; in order to "open" a boxed
existential that has directly adopted a class reference, temporary scratch
space may need to have been allocated.
sil-instruction ::= 'open_existential_box_value' sil-operand 'to' sil-type
%1 = open_existential_box_value %0 : $P to $@opened P
// %0 must be a value of boxed protocol or protocol composition type $P
// %@opened P must be a unique archetype that refers to an opened
// existential type P
// %1 will be of type $@opened P
Projects the value inside a boxed existential container, and uses the enclosed
type and protocol conformance metadata to bind the opened archetype $@opened
P
.
sil-instruction ::= 'dealloc_existential_box' sil-operand, sil-type
dealloc_existential_box %0 : $P, $T
// %0 must be an uninitialized box of boxed existential container type $P
// $T must be the AST type for which the box was allocated
Deallocates a boxed existential container. The value inside the existential
buffer is not destroyed; either the box must be uninitialized, or the value
must have been projected out and destroyed beforehand. It is undefined behavior
if the concrete type $T
is not the same type for which the box was
allocated with alloc_existential_box
.
sil-instruction ::= 'project_block_storage' sil-operand ':' sil-type
TODO Fill this in. The printing of this instruction looks incomplete on trunk currently.
These instructions implement type conversions which are not checked. These are either user-level conversions that are always safe and do not need to be checked, or implementation detail conversions that are unchecked for performance or flexibility.
sil-instruction ::= 'upcast' sil-operand 'to' sil-type
%1 = upcast %0 : $D to $B
// $D and $B must be class types or metatypes, with B a superclass of D
// %1 will have type $B
Represents a conversion from a derived class instance or metatype to a superclass, or from a base-class-constrained archetype to its base class.
sil-instruction ::= 'address_to_pointer' sil-operand 'to' sil-type
%1 = address_to_pointer %0 : $*T to $Builtin.RawPointer
// %0 must be of an address type $*T
// %1 will be of type Builtin.RawPointer
Creates a Builtin.RawPointer
value corresponding to the address %0
.
Converting the result pointer back to an address of the same type will give
an address equivalent to %0
. It is undefined behavior to cast the
RawPointer
to any address type other than its original address type or
any layout compatible types.
sil-instruction ::= 'pointer_to_address' sil-operand 'to' ('[' 'strict' ']')? sil-type
%1 = pointer_to_address %0 : $Builtin.RawPointer to [strict] $*T
// %1 will be of type $*T
Creates an address value corresponding to the Builtin.RawPointer
value
%0
. Converting a RawPointer
back to an address of the same type as
its originating address_to_pointer
instruction gives back an equivalent
address. It is undefined behavior to cast the RawPointer
back to any type
other than its original address type or layout compatible types. It is
also undefined behavior to cast a RawPointer
from a heap object to any
address type.
The strict
flag indicates whether the returned address adheres to
strict aliasing. If true, then the type of each memory access
dependent on this address must be consistent with the memory's bound
type. A memory access from an address that is not strict cannot have
its address substituted with a strict address, even if other nearby
memory accesses at the same location are strict.
sil-instruction ::= 'unchecked_ref_cast' sil-operand 'to' sil-type
%1 = unchecked_ref_cast %0 : $A to $B
// %0 must be an object of type $A
// $A must be a type with retainable pointer representation
// %1 will be of type $B
// $B must be a type with retainable pointer representation
Converts a heap object reference to another heap object reference type. This conversion is unchecked, and it is undefined behavior if the destination type is not a valid type for the heap object. The heap object reference on either side of the cast may be a class existential, and may be wrapped in one level of Optional.
sil-instruction ::= 'unchecked_ref_cast_addr'
sil-type 'in' sil-operand 'to'
sil-type 'in' sil-operand
unchecked_ref_cast_addr $A in %0 : $*A to $B in %1 : $*B
// %0 must be the address of an object of type $A
// $A must be a type with retainable pointer representation
// %1 must be the address of storage for an object of type $B
// $B must be a retainable pointer representation
Loads a heap object reference from an address and stores it at the address of another uninitialized heap object reference. The loaded reference is always taken, and the stored reference is initialized. This conversion is unchecked, and it is undefined behavior if the destination type is not a valid type for the heap object. The heap object reference on either side of the cast may be a class existential, and may be wrapped in one level of Optional.
sil-instruction ::= 'unchecked_addr_cast' sil-operand 'to' sil-type
%1 = unchecked_addr_cast %0 : $*A to $*B
// %0 must be an address
// %1 will be of type $*B
Converts an address to a different address type. Using the resulting
address is undefined unless B
is layout compatible with A
. The
layout of B
may be smaller than that of A
as long as the lower
order bytes have identical layout.
sil-instruction ::= 'unchecked_trivial_bit_cast' sil-operand 'to' sil-type
%1 = unchecked_trivial_bit_cast %0 : $Builtin.NativeObject to $Builtin.Word
// %0 must be an object.
// %1 must be an object with trivial type.
Bitcasts an object of type A
to be of same sized or smaller type
B
with the constraint that B
must be trivial. This can be used
for bitcasting among trivial types, but more importantly is a one way
bitcast from non-trivial types to trivial types.
sil-instruction ::= 'unchecked_bitwise_cast' sil-operand 'to' sil-type
%1 = unchecked_bitwise_cast %0 : $A to $B
Bitwise copies an object of type A
into a new object of type B
of the same size or smaller.
sil-instruction ::= 'ref_to_raw_pointer' sil-operand 'to' sil-type
%1 = ref_to_raw_pointer %0 : $C to $Builtin.RawPointer
// $C must be a class type, or Builtin.NativeObject, or AnyObject
// %1 will be of type $Builtin.RawPointer
Converts a heap object reference to a Builtin.RawPointer
. The RawPointer
result can be cast back to the originating class type but does not have
ownership semantics. It is undefined behavior to cast a RawPointer
from a
heap object reference to an address using pointer_to_address
.
sil-instruction ::= 'raw_pointer_to_ref' sil-operand 'to' sil-type
%1 = raw_pointer_to_ref %0 : $Builtin.RawPointer to $C
// $C must be a class type, or Builtin.NativeObject, or AnyObject
// %1 will be of type $C
Converts a Builtin.RawPointer
back to a heap object reference. Casting
a heap object reference to Builtin.RawPointer
back to the same type gives
an equivalent heap object reference (though the raw pointer has no ownership
semantics for the object on its own). It is undefined behavior to cast a
RawPointer
to a type unrelated to the dynamic type of the heap object.
It is also undefined behavior to cast a RawPointer
from an address to any
heap object type.
sil-instruction ::= 'ref_to_unowned' sil-operand
%1 = unowned_to_ref %0 : T
// $T must be a reference type
// %1 will have type $@unowned T
Adds the @unowned
qualifier to the type of a reference to a heap
object. No runtime effect.
sil-instruction ::= 'unowned_to_ref' sil-operand
%1 = unowned_to_ref %0 : $@unowned T
// $T must be a reference type
// %1 will have type $T
Strips the @unowned
qualifier off the type of a reference to a
heap object. No runtime effect.
TODO
TODO
sil-instruction ::= 'convert_function' sil-operand 'to'
('[' 'without_actually_escaping' ']')?
sil-type
%1 = convert_function %0 : $T -> U to $T' -> U'
// %0 must be of a function type $T -> U ABI-compatible with $T' -> U'
// (see below)
// %1 will be of type $T' -> U'
Performs a conversion of the function %0
to type T
, which must be ABI-
compatible with the type of %0
. Function types are ABI-compatible if their
input and result types are tuple types that, after destructuring, differ only
in the following ways:
- Corresponding tuple elements may add, remove, or change keyword names.
(a:Int, b:Float, UnicodeScalar) -> ()
and(x:Int, Float, z:UnicodeScalar) -> ()
are ABI compatible. - A class tuple element of the destination type may be a superclass or subclass of the source type's corresponding tuple element.
The function types may also differ in attributes, except that the
convention
attribute cannot be changed and the @noescape
attribute must
not change for functions with context.
A convert_function
cannot be used to change a thick type's @noescape
attribute (@noescape
function types with context are not ABI compatible with
escaping function types with context) -- however, thin function types with and
without @noescape
are ABI compatible because they have no context. To
convert from an escaping to a @noescape
thick function type use
convert_escape_to_noescape
.
With the without_actually_escaping
attribute, the
convert_function
may be used to convert a non-escaping closure
into an escaping function type. This attribute must be present
whenever the closure operand has an unboxed capture (via
@inout_aliasable) and the resulting function type is escaping. (This
only happens as a result of withoutActuallyEscaping()). If the
attribute is present then the resulting function type must be
escaping, but the operand's function type may or may not be
@noescape. Note that a non-escaping closure may have unboxed captured
even though its SIL function type is "escaping".
sil-instruction ::= 'convert_escape_to_noescape' sil-operand 'to' sil-type
%1 = convert_escape_to_noescape %0 : $T -> U to $@noescape T' -> U'
// %0 must be of a function type $T -> U ABI-compatible with $T' -> U'
// (see convert_function)
// %1 will be of the trivial type $@noescape T -> U
Converts an escaping (non-trivial) function type to an @noescape
trivial
function type. Something must guarantee the lifetime of the input %0
for the
duration of the use %1
.
A convert_escape_to_noescape [not_guaranteed] %opd
indicates that the
lifetime of its operand was not guaranteed by SILGen and a mandatory pass must
be run to ensure the lifetime of %opd`
for the conversion's uses.
A convert_escape_to_noescape [escaped]
indicates that the result was
passed to a function (materializeForSet) which escapes the closure in a way not
expressed by the convert's users. The mandatory pass must ensure the lifetime
in a conservative way.
TODO
TODO
sil-instruction ::= 'classify_bridge_object' sil-operand
%1 = classify_bridge_object %0 : $Builtin.BridgeObject
// %1 will be of type (Builtin.Int1, Builtin.Int1)
Decodes the bit representation of the specified Builtin.BridgeObject
value,
returning two bits: the first indicates whether the object is an Objective-C
object, the second indicates whether it is an Objective-C tagged pointer value.
sil-instruction ::= 'value_to_bridge_object' sil-operand
%1 = value_to_bridge_object %0 : $T
// %1 will be of type Builtin.BridgeObject
Sets the BridgeObject to a tagged pointer representation holding its operands by tagging and shifting the operand if needed:
value_to_bridge_object %x ===
(x << _swift_abi_ObjCReservedLowBits) | _swift_BridgeObject_TaggedPointerBits
%x
thus must not be using any high bits shifted away or the tag bits post-shift.
ARC operations on such tagged values are NOPs.
sil-instruction ::= 'ref_to_bridge_object' sil-operand, sil-operand
%2 = ref_to_bridge_object %0 : $C, %1 : $Builtin.Word
// %1 must be of reference type $C
// %2 will be of type Builtin.BridgeObject
Creates a Builtin.BridgeObject
that references %0
, with spare bits
in the pointer representation populated by bitwise-OR-ing in the value of
%1
. It is undefined behavior if this bitwise OR operation affects the
reference identity of %0
; in other words, after the following instruction
sequence:
%b = ref_to_bridge_object %r : $C, %w : $Builtin.Word
%r2 = bridge_object_to_ref %b : $Builtin.BridgeObject to $C
%r
and %r2
must be equivalent. In particular, it is assumed that
retaining or releasing the BridgeObject
is equivalent to retaining or
releasing the original reference, and that the above ref_to_bridge_object
/ bridge_object_to_ref
round-trip can be folded away to a no-op.
On platforms with ObjC interop, there is additionally a platform-specific
bit in the pointer representation of a BridgeObject
that is reserved to
indicate whether the referenced object has native Swift refcounting. It is
undefined behavior to set this bit when the first operand references an
Objective-C object.
sil-instruction ::= 'bridge_object_to_ref' sil-operand 'to' sil-type
%1 = bridge_object_to_ref %0 : $Builtin.BridgeObject to $C
// $C must be a reference type
// %1 will be of type $C
Extracts the object reference from a Builtin.BridgeObject
, masking out any
spare bits.
sil-instruction ::= 'bridge_object_to_word' sil-operand 'to' sil-type
%1 = bridge_object_to_word %0 : $Builtin.BridgeObject to $Builtin.Word
// %1 will be of type $Builtin.Word
Provides the bit pattern of a Builtin.BridgeObject
as an integer.
sil-instruction ::= 'thin_to_thick_function' sil-operand 'to' sil-type
%1 = thin_to_thick_function %0 : $@convention(thin) T -> U to $T -> U
// %0 must be of a thin function type $@convention(thin) T -> U
// The destination type must be the corresponding thick function type
// %1 will be of type $T -> U
Converts a thin function value, that is, a bare function pointer with no
context information, into a thick function value with ignored context.
Applying the resulting thick function value is equivalent to applying the
original thin value. The thin_to_thick_function
conversion may be
eliminated if the context is proven not to be needed.
sil-instruction ::= 'thick_to_objc_metatype' sil-operand 'to' sil-type
%1 = thick_to_objc_metatype %0 : $@thick T.Type to $@objc_metatype T.Type
// %0 must be of a thick metatype type $@thick T.Type
// The destination type must be the corresponding Objective-C metatype type
// %1 will be of type $@objc_metatype T.Type
Converts a thick metatype to an Objective-C class metatype. T
must
be of class, class protocol, or class protocol composition type.
sil-instruction ::= 'objc_to_thick_metatype' sil-operand 'to' sil-type
%1 = objc_to_thick_metatype %0 : $@objc_metatype T.Type to $@thick T.Type
// %0 must be of an Objective-C metatype type $@objc_metatype T.Type
// The destination type must be the corresponding thick metatype type
// %1 will be of type $@thick T.Type
Converts an Objective-C class metatype to a thick metatype. T
must
be of class, class protocol, or class protocol composition type.
TODO
TODO
Some user-level cast operations can fail and thus require runtime checking.
The unconditional_checked_cast_addr, unconditional_checked_cast_value and unconditional_checked_cast instructions performs an unconditional checked cast; it is a runtime failure if the cast fails. The checked_cast_addr_br, checked_cast_value_br and checked_cast_br terminator instruction performs a conditional checked cast; it branches to one of two destinations based on whether the cast succeeds or not.
sil-instruction ::= 'unconditional_checked_cast' sil-operand 'to' sil-type
%1 = unconditional_checked_cast %0 : $A to $B
%1 = unconditional_checked_cast %0 : $*A to $*B
// $A and $B must be both objects or both addresses
// %1 will be of type $B or $*B
Performs a checked scalar conversion, causing a runtime failure if the conversion fails. Casts that require changing representation or ownership are unsupported.
sil-instruction ::= 'unconditional_checked_cast_addr'
sil-type 'in' sil-operand 'to'
sil-type 'in' sil-operand
unconditional_checked_cast_addr $A in %0 : $*@thick A to $B in $*@thick B
// $A and $B must be both addresses
// %1 will be of type $*B
// $A is destroyed during the conversion. There is no implicit copy.
Performs a checked indirect conversion, causing a runtime failure if the conversion fails.
sil-instruction ::= 'unconditional_checked_cast_value'
sil-operand 'to' sil-type
%1 = unconditional_checked_cast_value %0 : $A to $B
// $A must not be an address
// $B must not be an address
// %1 will be of type $B
// $A is destroyed during the conversion. There is no implicit copy.
Performs a checked conversion, causing a runtime failure if the conversion fails. Unlike unconditional_checked_cast, this destroys its operand and creates a new value. Consequently, this supports bridging objects to values, as well as casting to a different ownership classification such as $AnyObject to $T.Type.
sil-instruction ::= 'cond_fail' sil-operand
cond_fail %0 : $Builtin.Int1
// %0 must be of type $Builtin.Int1
This instruction produces a runtime failure if the operand is one. Execution proceeds normally if the operand is zero.
These instructions terminate a basic block. Every basic block must end with a terminator. Terminators may only appear as the final instruction of a basic block.
sil-terminator ::= 'unreachable'
unreachable
Indicates that control flow must not reach the end of the current basic block.
It is a dataflow error if an unreachable terminator is reachable from the entry
point of a function and is not immediately preceded by an apply
of a
no-return function.
sil-terminator ::= 'return' sil-operand
return %0 : $T
// $T must be the return type of the current function
Exits the current function and returns control to the calling function. If
the current function was invoked with an apply
instruction, the result
of that function will be the operand of this return
instruction. If
the current function was invoked with a try_apply
instruction, control
resumes at the normal destination, and the value of the basic block argument
will be the operand of this return
instruction.
If the current function is a yield_once
coroutine, there must not be
a path from the entry block to a return
which does not pass through
a yield
instruction. This rule does not apply in the raw
SIL stage.
return
does not retain or release its operand or any other values.
A function must not contain more than one return
instruction.
sil-terminator ::= 'throw' sil-operand
throw %0 : $T
// $T must be the error result type of the current function
Exits the current function and returns control to the calling
function. The current function must have an error result, and so the
function must have been invoked with a try_apply
instruction.
Control will resume in the error destination of that instruction, and
the basic block argument will be the operand of the throw
.
throw
does not retain or release its operand or any other values.
A function must not contain more than one throw
instruction.
sil-terminator ::= 'yield' sil-yield-values
',' 'resume' sil-identifier
',' 'unwind' sil-identifier
sil-yield-values ::= sil-operand
sil-yield-values ::= '(' (sil-operand (',' sil-operand)*)? ')'
Temporarily suspends the current function and provides the given
values to the calling function. The current function must be a coroutine,
and the yield values must match the yield types of the coroutine.
If the calling function resumes the coroutine normally, control passes to
the resume
destination. If the calling function aborts the coroutine,
control passes to the unwind
destination.
The resume
and unwind
destination blocks must be uniquely
referenced by the yield
instruction. This prevents them from becoming
critical edges.
In a yield_once
coroutine, there must not be a control flow path leading
from the resume
edge to another yield
instruction in this function.
This rule does not apply in the raw
SIL stage.
There must not be a control flow path leading from the unwind
edge to
a return
instruction, to a throw
instruction, or to any block
reachable from the entry block via a path that does not pass through
an unwind
edge. That is, the blocks reachable from unwind
edges
must jointly form a disjoint subfunction of the coroutine.
sil-terminator ::= 'unwind'
Exits the current function and returns control to the calling function,
completing an unwind from a yield
. The current function must be a
coroutine.
unwind
is only permitted in blocks reachable from the unwind
edges
of yield
instructions.
sil-terminator ::= 'br' sil-identifier
'(' (sil-operand (',' sil-operand)*)? ')'
br label (%0 : $A, %1 : $B, ...)
// `label` must refer to a basic block label within the current function
// %0, %1, etc. must be of the types of `label`'s arguments
Unconditionally transfers control from the current basic block to the block
labeled label
, binding the given values to the arguments of the destination
basic block.
sil-terminator ::= 'cond_br' sil-operand ','
sil-identifier '(' (sil-operand (',' sil-operand)*)? ')' ','
sil-identifier '(' (sil-operand (',' sil-operand)*)? ')'
cond_br %0 : $Builtin.Int1, true_label (%a : $A, %b : $B, ...), \
false_label (%x : $X, %y : $Y, ...)
// %0 must be of $Builtin.Int1 type
// `true_label` and `false_label` must refer to block labels within the
// current function and must not be identical
// %a, %b, etc. must be of the types of `true_label`'s arguments
// %x, %y, etc. must be of the types of `false_label`'s arguments
Conditionally branches to true_label
if %0
is equal to 1
or to
false_label
if %0
is equal to 0
, binding the corresponding set of
values to the arguments of the chosen destination block.
sil-terminator ::= 'switch_value' sil-operand
(',' sil-switch-value-case)*
(',' sil-switch-default)?
sil-switch-value-case ::= 'case' sil-value ':' sil-identifier
sil-switch-default ::= 'default' sil-identifier
switch_value %0 : $Builtin.Int<n>, case %1: label1, \
case %2: label2, \
..., \
default labelN
// %0 must be a value of builtin integer type $Builtin.Int<n>
// `label1` through `labelN` must refer to block labels within the current
// function
// FIXME: All destination labels currently must take no arguments
Conditionally branches to one of several destination basic blocks based on a
value of builtin integer or function type. If the operand value matches one of the case
values of the instruction, control is transferred to the corresponding basic
block. If there is a default
basic block, control is transferred to it if
the value does not match any of the case
values. It is undefined behavior
if the value does not match any cases and no default
branch is provided.
sil-instruction ::= 'select_value' sil-operand sil-select-value-case*
(',' 'default' sil-value)?
':' sil-type
sil-select-value-case ::= 'case' sil-value ':' sil-value
%n = select_value %0 : $U, \
case %c1: %r1, \
case %c2: %r2, /* ... */ \
default %r3 : $T
// $U must be a builtin type. Only integers types are supported currently.
// c1, c2, etc must be of type $U
// %r1, %r2, %r3, etc. must have type $T
// %n has type $T
Selects one of the "case" or "default" operands based on the case of a value. This is equivalent to a trivial switch_value branch sequence:
entry:
switch_value %0 : $U, \
case %c1: bb1, \
case %c2: bb2, /* ... */ \
default bb_default
bb1:
br cont(%r1 : $T) // value for %c1
bb2:
br cont(%r2 : $T) // value for %c2
bb_default:
br cont(%r3 : $T) // value for default
cont(%n : $T):
// use argument %n
but turns the control flow dependency into a data flow dependency.
sil-terminator ::= 'switch_enum' sil-operand
(',' sil-switch-enum-case)*
(',' sil-switch-default)?
sil-switch-enum-case ::= 'case' sil-decl-ref ':' sil-identifier
switch_enum %0 : $U, case #U.Foo!enumelt: label1, \
case #U.Bar!enumelt: label2, \
..., \
default labelN
// %0 must be a value of enum type $U
// #U.Foo, #U.Bar, etc. must be 'case' declarations inside $U
// `label1` through `labelN` must refer to block labels within the current
// function
// label1 must take either no basic block arguments, or a single argument
// of the type of #U.Foo's data
// label2 must take either no basic block arguments, or a single argument
// of the type of #U.Bar's data, etc.
// labelN must take no basic block arguments
Conditionally branches to one of several destination basic blocks based on the
discriminator in a loadable enum
value. Unlike switch_int
,
switch_enum
requires coverage of the operand type: If the enum
type
cannot be switched exhaustively in the current function, the default
branch
is required; otherwise, the default
branch is required unless a destination
is assigned to every case
of the enum
. The destination basic block for
a case
may take an argument of the corresponding enum
case
's data
type (or of the address type, if the operand is an address). If the branch is
taken, the destination's argument will be bound to the associated data inside
the original enum value. For example:
enum Foo {
case Nothing
case OneInt(Int)
case TwoInts(Int, Int)
}
sil @sum_of_foo : $Foo -> Int {
entry(%x : $Foo):
switch_enum %x : $Foo, \
case #Foo.Nothing!enumelt: nothing, \
case #Foo.OneInt!enumelt.1: one_int, \
case #Foo.TwoInts!enumelt.1: two_ints
nothing:
%zero = integer_literal $Int, 0
return %zero : $Int
one_int(%y : $Int):
return %y : $Int
two_ints(%ab : $(Int, Int)):
%a = tuple_extract %ab : $(Int, Int), 0
%b = tuple_extract %ab : $(Int, Int), 1
%add = function_ref @add : $(Int, Int) -> Int
%result = apply %add(%a, %b) : $(Int, Int) -> Int
return %result : $Int
}
On a path dominated by a destination block of switch_enum
, copying or
destroying the basic block argument has equivalent reference counting semantics
to copying or destroying the switch_enum
operand:
// This retain_value...
retain_value %e1 : $Enum
switch_enum %e1, case #Enum.A: a, case #Enum.B: b
a(%a : $A):
// ...is balanced by this release_value
release_value %a
b(%b : $B):
// ...and this one
release_value %b
sil-terminator ::= 'switch_enum_addr' sil-operand
(',' sil-switch-enum-case)*
(',' sil-switch-default)?
switch_enum_addr %0 : $*U, case #U.Foo!enumelt: label1, \
case #U.Bar!enumelt: label2, \
..., \
default labelN
// %0 must be the address of an enum type $*U
// #U.Foo, #U.Bar, etc. must be cases of $U
// `label1` through `labelN` must refer to block labels within the current
// function
// The destinations must take no basic block arguments
Conditionally branches to one of several destination basic blocks based on the discriminator in the enum value referenced by the address operand.
Unlike switch_int
, switch_enum
requires coverage of the operand type:
If the enum
type cannot be switched exhaustively in the current function,
the default
branch is required; otherwise, the default
branch is
required unless a destination is assigned to every case
of the enum
.
Unlike switch_enum
, the payload value is not passed to the destination
basic blocks; it must be projected out separately with
unchecked_take_enum_data_addr.
sil-terminator ::= 'dynamic_method_br' sil-operand ',' sil-decl-ref
',' sil-identifier ',' sil-identifier
dynamic_method_br %0 : $P, #X.method!1, bb1, bb2
// %0 must be of protocol type
// #X.method!1 must be a reference to an @objc method of any class
// or protocol type
Looks up the implementation of an Objective-C method with the same
selector as the named method for the dynamic type of the value inside
an existential container. The "self" operand of the result function
value is represented using an opaque type, the value for which must be
projected out as a value of type Builtin.ObjCPointer
.
If the operand is determined to have the named method, this
instruction branches to bb1
, passing it the uncurried function
corresponding to the method found. If the operand does not have the
named method, this instruction branches to bb2
.
sil-terminator ::= 'checked_cast_br' sil-checked-cast-exact?
sil-operand 'to' sil-type ','
sil-identifier ',' sil-identifier
sil-checked-cast-exact ::= '[' 'exact' ']'
checked_cast_br %0 : $A to $B, bb1, bb2
checked_cast_br %0 : $*A to $*B, bb1, bb2
checked_cast_br [exact] %0 : $A to $A, bb1, bb2
// $A and $B must be both object types or both address types
// bb1 must take a single argument of type $B or $*B
// bb2 must take no arguments
Performs a checked scalar conversion from $A
to $B
. If the conversion
succeeds, control is transferred to bb1
, and the result of the cast is
passed into bb1
as an argument. If the conversion fails, control is
transferred to bb2
.
An exact cast checks whether the dynamic type is exactly the target type, not any possible subtype of it. The source and target types must be class types.
sil-terminator ::= 'checked_cast_value_br'
sil-operand 'to' sil-type ','
sil-identifier ',' sil-identifier
sil-checked-cast-exact ::= '[' 'exact' ']'
checked_cast_value_br %0 : $A to $B, bb1, bb2
// $A must be not be an address
// $B must be an opaque value
// bb1 must take a single argument of type $B
// bb2 must take no arguments
Performs a checked opaque conversion from $A
to $B
. If the conversion
succeeds, control is transferred to bb1
, and the result of the cast is
passed into bb1
as an argument. If the conversion fails, control is
transferred to bb2
.
sil-terminator ::= 'checked_cast_addr_br'
sil-cast-consumption-kind
sil-type 'in' sil-operand 'to'
sil-stype 'in' sil-operand ','
sil-identifier ',' sil-identifier
sil-cast-consumption-kind ::= 'take_always'
sil-cast-consumption-kind ::= 'take_on_success'
sil-cast-consumption-kind ::= 'copy_on_success'
checked_cast_addr_br take_always $A in %0 : $*@thick A to $B in %2 : $*@thick B, bb1, bb2
// $A and $B must be both address types
// bb1 must take a single argument of type $*B
// bb2 must take no arguments
Performs a checked indirect conversion from $A
to $B
. If the
conversion succeeds, control is transferred to bb1
, and the result of the
cast is left in the destination. If the conversion fails, control is
transferred to bb2
.
sil-terminator ::= 'try_apply' sil-value
sil-apply-substitution-list?
'(' (sil-value (',' sil-value)*)? ')'
':' sil-type
'normal' sil-identifier, 'error' sil-identifier
try_apply %0(%1, %2, ...) : $(A, B, ...) -> (R, @error E),
normal bb1, error bb2
bb1(%3 : R):
bb2(%4 : E):
// Note that the type of the callee '%0' is specified *after* the arguments
// %0 must be of a concrete function type $(A, B, ...) -> (R, @error E)
// %1, %2, etc. must be of the argument types $A, $B, etc.
Transfers control to the function specified by %0
, passing it the
given arguments. When %0
returns, control resumes in either the
normal destination (if it returns with return
) or the error
destination (if it returns with throw
).
%0
must have a function type with an error result.
The rules on generic substitutions are identical to those of apply
.
To be able to support disabling assertions at compile time there is a builtin
assertion_configuration
function. A call to this function can be replaced at
compile time by a constant or can stay opaque.
All calls to the assert_configuration
function are replaced by the constant
propagation pass to the appropriate constant depending on compile time settings.
Subsequent passes remove dependent unwanted control flow. Using this mechanism
we support conditionally enabling/disabling of code in SIL libraries depending
on the assertion configuration selected when the library is linked into user
code.
There are three assertion configurations: Debug (0), Release (1) and DisableReplacement (-1).
The optimization flag or a special assert configuration flag determines the value. Depending on the configuration value assertions in the standard library will be executed or not.
The standard library uses this builtin to define an assert that can be disabled at compile time.
func assert(...) {
if (Int32(Builtin.assert_configuration()) == 0) {
_fatal_error_message(message, ...)
}
}
The assert_configuration
function application is serialized when we build
the standard library (we recognize the -parse-stdlib
option and don't do the
constant replacement but leave the function application to be serialized to
sil).
The compiler flag that influences the value of the assert_configuration
function application is the optimization flag: at -Onone
the application will
be replaced by Debug
at higher optimization levels the instruction will be
replaced by Release
. Optionally, the value to use for replacement can be
specified with the -assert-config
flag which overwrites the value selected by
the optimization flag (possible values are Debug
, Release
,
DisableReplacement
).
If the call to the assert_configuration
function stays opaque until IRGen,
IRGen will replace the application by the constant representing Debug mode (0).
This happens we can build the standard library .dylib. The generate sil will
retain the function call but the generated .dylib will contain code with
assertions enabled.