Contents
- Abstract
- SIL in the Swift Compiler
- Syntax
- Dataflow Errors
- Runtime Failure
- Undefined Behavior
- Calling Convention
- Type Based Alias Analysis
- Instruction Set
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.
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 -O0, 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 -O0.
- 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.
transparentfunction 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_boxinstructions toalloc_stack, and the second of which promotes non-address-exposedalloc_stackinstructions 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 of the end" of its definition, which is an error.
It also issues an error when a
noreturnfunction returns.
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 -O0.
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 gener ic 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 types witness table and replaces the indirect virtual call with a call to the mapped function.
- Performance Inlining
- Reference Counting Optimizations
- Memory Promotion/Optimizations
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 @_TSsoi1pfTSdSd_Sd
%2 = struct_extract %0 : $Point, #Point.x
%3 = struct_extract %0 : $Point, #Point.y
%4 = apply %1(%2, %3) : $(Double, Double) -> Double
%5 = return %4 : Double
}
// Define a SIL vtable. This matches dynamically-dispatched method
// identifiers to their implementations for a known static class type.
sil_vtable Button {
#Button.onClick!1: @_TC5norms6Button7onClickfS0_FT_T_
#Button.onMouseDown!1: @_TC5norms6Button11onMouseDownfS0_FT_T_
#Button.onMouseUp!1: @_TC5norms6Button9onMouseUpfS0_FT_T_
}
decl ::= sil-stage-decl sil-stage-decl ::= 'sil_stage' sil-stage sil-stage ::= 'raw' sil-stage ::= 'canonical'
There are different invariants on SIL depending on what stage of processing has been applied to it.
- Raw SIL is the form produced by SILGen that has not been run through
guaranteed optimizations or diagnostic passes. Raw SIL may not have a
fully-constructed SSA graph. It may contain dataflow errors. Some instructions
may be represented in non-canonical forms, such as
assignanddestroy_addrfor non-address-only values. Raw SIL should not be used for native code generation or distribution. - Canonical SIL is SIL as it exists after guaranteed optimizations and diagnostics. Dataflow errors must be eliminated, and certain instructions must be canonicalized to simpler forms. Performance optimization and native code generation are derived from this form, and a module can be distributed containing SIL in this (or later) forms.
SIL files declare the processing stage of the included SIL with one of the
declarations sil_stage raw or sil_stage canonical at top level. Only
one such declaration may appear in a file.
sil-type ::= '$' '*'? 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
generateArrayfor 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
generatordepending 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 (@out Float, @in (Int,Int)) -> ()``.
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 (@out Float, @in Int, @inout Int)
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 - the address of local storage of a legal SIL type,
$*@local_storage T.
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 tuple type whose element types are legal SIL types, or
- it is a legal Swift type that is not a function, tuple, or l-value 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.
The address of local storage for T $*@local_storage T is a
handle to a stack allocation of a variable of type $T.
For many types, the handle for a stack allocation is simply the
allocated address itself. However, if a type is runtime-sized, the
compiler must emit code to potentially dynamically allocate memory.
SIL abstracts over such differences by using values of local-storage
type as the first result of alloc_stack and the operand of
dealloc_stack.
Local-storage address types are not first-class in the same sense that address types are not first-class.
The self type for T sil_self T refers to the Self type
within the protocol T.
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_refwill give a value of generic function type.A SIL function type declares its conventional treatment of its context value:
- If it is
@thin, the function requires no context value. - If it is
@callee_owned, the context value is treated as an owned direct parameter. - If it is
@callee_guaranteed, the context value is treated as a guaranteed direct parameter. - Otherwise, the context value is treated as an unowned direct parameter.
- If it is
A SIL function type declares the conventions for its parameters, including any implicit out-parameters. The parameters are written as an unlabelled 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
@inparameter is indirect. The address must be of an initialized object; the function is responsible for destroying the value held there. - An
@inoutparameter is indirect. The address must be of an initialized object, and the function must leave an initialized object there upon exit. - An
@outparameter is indirect. The address must be of an uninitialized object; the function is responsible for initializing a value there. If there is an@outparameter, it must be the first parameter, and the direct result must be(). - An
@ownedparameter is an owned direct parameter. - A
@guaranteedparameter is a guaranteed direct parameter. - Otherwise, the parameter is an unowned direct parameter.
- An
A SIL function type declares the convention for its direct result. The result must be a legal SIL type.
- An
@ownedresult is an owned direct result. - An
@autoreleasedresult is an autoreleased 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_retaining 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. It may have been autoreleased, and the caller
should take action to reclaim that autorelease with
strong_retain_autoreleased.
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_addranddestroy_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.ObjectPointerandBuiltin.ObjCPointertypes, 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
idtype. 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 ofOptionalorImplicitlyUnwrappedOptionalapplied to any of the above. Types with retainable pointer representation can be returned via the@autoreleasedreturn 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 calling convention of the function, indicated by the
@cc(convention)
attribute—where convention can currently be
swift,method,cdecl, orobjc_method—describing a machine-level calling convention below the concern of SIL.The thinness of the function reference, indicated by the
@thinattribute, which tracks whether a function reference requires a context value to reference captured closure state. Standalone functions and methods are always@thin, but function-local functions or closure expressions that capture context are thick. Partial applications of curried functions or methods are also thick.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) -> Cmight 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.
TODO: Type-checking of cc and thin attributes will move into Swift's type-checker and out of SIL eventually.
(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
$*Ucan be cast byaddress_to_pointer/pointer_to_addressto$*Tand a valid value of typeTcan be loaded out (or indirectly used, ifTis address- only), - if
Tis a nontrivial type, thenretain_value/release_valueof the loadedTvalue is equivalent toretain_value/release_valueof the originalUvalue.
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.RawPointeris commutatively layout compatible with all heap object reference types, andOptionalof heap object reference types. (Note thatRawPointeris a trivial type, so does not have ownership semantics.)Builtin.RawPointeris 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
Band a derived classDinheriting fromB, a value of typeBreferencing an instance of typeDis layout compatible with bothBandD, as well asBuiltin.NativeObjectandBuiltin.UnknownObject. 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 ('#' [0-9]+)?
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.
In SIL, a single instruction may produce multiple values. Operands that refer
to multiple-value instructions choose the value by following the %name with
# and the index of the value. For example:
// alloc_box produces two values--the refcounted pointer %box#0, and the // value address %box#1 %box = alloc_box $Int64 // Refer to the refcounted pointer strong_retain %box#0 : $Builtin.ObjectPointer // Refer to the address store %value to %box#1 : $*Int64
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-def ::= (sil-value-name '=')? sil-instruction
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):
%1 = 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 ()
%4 = return %3 : $()
}
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 avardeclarationsetter: the setter function for avardeclarationallocator: astructorenumconstructor, or aclass's allocating constructorinitializer: aclass's initializing constructorenumelt: a member of aenumtype.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 Swiftfuncforeign: 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 : $@thin (x:A) -> (y:B) -> (z:C) -> D #example.foo!1 : $@thin ((y:B), (x:A)) -> (z:C) -> D #example.foo!2 : $@thin ((z:C), (y:B), (x:A)) -> D
The deepest uncurry level is referred to as the natural uncurry level.
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 @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'
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
publicorpublic_externallinkage is always visible.- An object with
hidden,hidden_external, orsharedlinkage is visible only to objects in the same Swift module.- An object with
privatelinkage 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
publicobject may be linked to apublic_externalobject.- A
hiddenobject may be linked to ahidden_externalobject.
If two objects are linked, at most one may be a definition, unless:
- both objects have
sharedlinkage 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.
publicdefinitions are unique and visible everywhere in the program. In LLVM IR, they will be emitted withexternallinkage anddefaultvisibility.hiddendefinitions are unique and visible only within the current Swift module. In LLVM IR, they will be emitted withexternallinkage andhiddenvisibility.privatedefinitions are unique and visible only within the current SIL module. In LLVM IR, they will be emitted withprivatelinkage.shareddefinitions are visible only within the current Swift module. They can be linked only with othershareddefinitions, which must be equivalent; therefore, they only need to be emitted if actually used. In LLVM IR, they will be emitted withlinkonce_odrlinkage andhiddenvisibility.public_externalandhidden_externalobjects 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 haveexternallinkage and definitions (if actually emitted as definitions) will haveavailable_externallylinkage.
decl ::= sil-vtable
sil-vtable ::= 'sil_vtable' identifier '{' sil-vtable-entry* '}'
sil-vtable-entry ::= sil-decl-ref ':' sil-function-name
SIL represents dynamic dispatch for class methods using the class_method,
super_method, and dynamic_method instructions. The potential destinations
for these dispatch operations 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 : $@thin (@owned A) -> ()
sil @A_bar : $@thin (@owned A) -> ()
sil @A_bas : $@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 : $@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 : $@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).
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-global-variable sil-global-variable ::= 'sil_global' sil-linkage identifier ':' sil-type
SIL representation of a global variable.
FIXME: to be written.
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 @noreturn functions. An unreachable instruction that survives
guaranteed DCE and is not immediately preceded by a @noreturn
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-owner 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 1 : $Int
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.
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 an @objc_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 alias. Swift, however, is memory-safe and statically
typed, so aliasing of classes is constrained by the type system as follows:
- A
Builtin.ObjectPointermay alias any native Swift heap object, including a Swift class instance, a box allocated byalloc_box, an array allocated byalloc_array, or a thick function's closure context. It may not alias natively Objective-C class instances. - A
Builtin.ObjCPointermay 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
$Cmay alias. Two values of related class type$Band$D, where there is a subclass relationship between$Band$D, may alias. Two values of unrelated class types may not alias. This includes different instantiations of a generic class type, such as$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>, becauseIntis a potential substitution forT.
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).
It is undefined behavior to perform a typed access to an address or reference if the stored object or referent is not an allocated object of 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, ignoring "blessed"
alias-introducing operations such as pointer_to_address, the bitcast
intrinsic, and the inttoptr intrinsic.
These instructions allocate and deallocate memory.
sil-instruction ::= 'alloc_stack' sil-type %1 = alloc_stack $T // %1#0 has type $*@local_storage T // %1#1 has type $*T
Allocates uninitialized memory that is sufficiently aligned on the stack
to contain a value of type T. The first result of the instruction
is a local-storage handle suitable for passing to dealloc_stack.
The second result of the instruction is the address of the allocated memory.
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' ']')? sil-type
%1 = alloc_ref $T
// $T must be a reference type
// %1 has type $T
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:).
sil-instruction ::= 'alloc_ref_dynamic' ('[' 'objc' ']')? sil-operand ',' sil-type
%1 = alloc_ref_dynamic %0 : $@thick T.Type, $T
%1 = alloc_ref_dynamic [objc] %0 : $@objc_metatype T.Type, $T
// $T must be a class type
// %1 has type $T
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 objc attribute
indicates that the object should be allocated using Objective-C's
allocation methods (+allocWithZone:).
sil-instruction ::= 'alloc_box' sil-type %1 = alloc_box $T // %1 has two values: // %1#0 has type $Builtin.ObjectPointer // %1#1 has type $*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 a two-value operand;
the first value is the reference-counted ObjectPointer that owns the box,
and the second value is 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_array' sil-type ',' sil-operand %1 = alloc_array $T, %0 : Builtin.Int<n> // $T must be a type // %0 must be of a builtin integer type // %1 has two values: // %1#0 has type Builtin.ObjectPointer // %1#1 has type *T
Allocates a box large enough to hold an array of %0 values of type T.
The result of the instruction is a two-value operand; the first value is the
reference-counted ObjectPointer that owns the box,
and the second value is the address of the first 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 array of values, and releasing it
to a retain count of zero destroys all of the contained values as if by
destroy_addr. Releasing the array is thus invalid unless all of the array's
value have been uninitialized. To deallocate a box
whose value has not been initialized, dealloc_box should be used.
sil-instruction ::= 'dealloc_stack' sil-operand dealloc_stack %0 : $*@local_storage T // %0 must be of a local-storage $*@local_storage 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 @local_storage of 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-type ',' sil-operand dealloc_box $Int, %0 : $Builtin.ObjectPointer
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 ::= 'dealloc_ref' sil-operand dealloc_ref %0 : $T // $T must be a class type
Deallocates a class type instance, bypassing the reference counting mechanism. The instance must have a retain count of one. The type of the operand must match the allocated type exactly, or else undefined behavior results.
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.
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_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.
sil-instruction ::= debug_value_addr sil-operand 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 ::= '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 ::= 'mark_uninitialized' '[' mu_kind ']' sil-operand mu_kind ::= 'var' mu_kind ::= 'rootself' mu_kind ::= 'derivedself' mu_kind ::= 'derivedselfonly' mu_kind ::= 'delegatingself' %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: designatesselfin a struct, enum, or root classderivedself: designatesselfin a derived (non-root) classderivedselfonly: designatesselfin a derived (non-root) class whose stored properties have already been initializeddelegatingself: designatesselfon a struct, enum, or class in a delegating constructor (one that calls self.init)
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.
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, produced by alloc_array or by an external function. 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 ::= '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 $*T
Given a Builtin.RawPointer value %0, returns a pointer value at the
byte offset %1 relative to %0.
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 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
@weakor@unownedreference as if it were a strong reference. - Consistency: when a reference is kept in memory, instructions like
copy_addranddestroy_addrimplicitly 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.
sil-instruction ::= 'strong_retain_autoreleased' sil-operand strong_retain_autoreleased %0 : $T // $T must have a retainable pointer representation
Retains the heap object referenced by %0 using the Objective-C ARC
"autoreleased return value" optimization. The operand must be the result of an
apply instruction with an Objective-C method callee, and the
strong_retain_autoreleased instruction must be first use of the value after
the defining apply instruction.
TODO: Specify all the other strong_retain_autoreleased constraints here.
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.
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 ::= '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.
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 refereced 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.
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.
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.
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 :: 'copy_block' sil-operand %1 = copy_block %0 : $@objc_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.
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 : $@thin T -> U // $@thin T -> U must be a thin function type // %1 has type $T -> U
Creates a reference to a SIL function.
sil-instruction ::= 'builtin_function_ref' sil-identifier ':' sil-type %1 = builtin_function_ref "foo" : $@thin T -> U // "foo" must name a function in the Builtin module // $@thin T -> U must be a thin function type // %1 has type $@thin T -> U
Creates a reference to a compiler builtin function.
sil-instruction ::= 'global_addr' sil-decl-ref ':' sil-type %1 = global_addr #foo.bar : $*T // #foo.bar must name a physical global variable declaration // $*T must be an address type // %1 has type $*T
TODO: Design of global variables subject to change.
Creates a reference to the address of a global variable.
sil-instruction ::= 'sil_global_addr' sil-global-name ':' sil-type %1 = sil_global_addr @foo : $*Builtin.Word
Creates a reference to the address of a sil global variable.
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' %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 nul-terminated. The
string literal value is specified using Swift's string
literal syntax (though \() interpolations are not allowed).
These instructions perform dynamic lookup of class and generic methods. They share a common set of attributes:
sil-method-attributes ::= '[' 'volatile'? ']'
The volatile attribute on a dynamic dispatch instruction indicates that
the method lookup is semantically required (as, for example, in Objective-C).
When the type of a dynamic dispatch instruction's operand is known,
optimization passes can promote non-volatile dispatch instructions
into static function_ref instructions.
If a dynamic dispatch instruction references an Objective-C method
(indicated by the foreign marker on a method reference, as in
#NSObject.description!1.foreign), then the instruction
represents an objc_msgSend invocation. 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. objc_msgSend invocations must always be volatile.
sil-instruction ::= 'class_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = class_method %0 : $T, #T.method!1 : $@thin U -> V
// %0 must be of a class type or class metatype $T
// #T.method!1 must be a reference to a dynamically-dispatched 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 and the method is not an Objective-C method.
If:
- the instruction is not
[volatile], - the referenced method is not a
foreignmethod, - and 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 ::= 'super_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = super_method %0 : $T, #Super.method!1.foreign : $@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 $@thin U -> V
Looks up a method in the superclass of a class or class metatype instance.
Note that for native Swift methods, super.method calls are statically
dispatched, so this instruction is only valid for Objective-C methods.
It is undefined behavior if the class value is null and the method is
not an Objective-C method.
sil-instruction ::= 'witness_method' sil-method-attributes?
sil-type ',' sil-decl-ref ':' sil-type
%1 = witness_method $T, #Proto.method!1 \
: $@thin @cc(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 $@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.
sil-instruction ::= 'protocol_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = protocol_method %0 : $P, #P.method!1 : $@thick @cc(witness_method) U -> V
// %0 must be of a protocol or protocol composition type $P,
// address of address-only protocol type $*P,
// or metatype of protocol type $P.metatype
// #P.method!1 must be a reference to a method of one of the protocols of P
//
// If %0 is an address-only protocol address, then the "self" argument of
// the method type must be $*@sil_self P, the Self archetype of P
// If %0 is a class protocol value, then the "self" argument of
// the method type must be $@sil_self P, the Self archetype of P
// If %0 is a protocol metatype, then the "self" argument of
// the method type must be P.metatype
Looks up the implementation of a protocol 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 of the same existential container as the protocol_method
operand:
- If the operand is the address of an address-only protocol type, then the
"self" argument of the method is of type
$*@sil_self P, theSelfarchetype of the method's protocol, and can be projected using theproject_existentialinstruction. - If the operand is a value of a class protocol type, then the "self"
argument of the method is of type
$@sil_self Pand can be projected using theproject_existential_refinstruction. - If the operand is a protocol metatype, it does not need to be projected, and the "self" argument of the method is the protocol metatype itself.
It is undefined behavior if the protocol_method function value is invoked
with a "self" argument not derived from the same existential container as the
method itself.
sil-instruction ::= 'dynamic_method' sil-method-attributes?
sil-operand ',' sil-decl-ref ':' sil-type
%1 = dynamic_method %0 : $P, #X.method!1 : $@thin U -> V
// %0 must be of a protocol or protocol composition type $P,
// where $P contains the Swift.DynamicLookup protocol
// #X.method!1 must be a reference to an @objc method of any class
// or protocol type
//
// The "self" argument of the method type $@thin U -> V must be
// Builtin.ObjCPointer
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.
It is undefined behavior if the dynamic type of the operand does not
have an implementation for the Objective-C method with the selector to
which the dynamic_method instruction refers, or if that
implementation has parameter or result types that are incompatible
with the method referenced by dynamic_method.
This instruction should only be used in cases where its result will be
immediately consumed by an operation that performs the selector check
itself (e.g., an apply that lowers to objc_msgSend).
To query whether the operand has an implementation for the given
method and safely handle the case where it does not, use
dynamic_method_br.
These instructions call functions or wrap them in partial application or specialization thunks.
sil-instruction ::= 'apply' 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<T = A, U = 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.
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.
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.
TODO: should have normal/unwind branch targets, like LLVM invoke.
sil-instruction ::= 'partial_apply' sil-value
sil-apply-substitution-list?
'(' (sil-value (',' sil-value)*)? ')'
':' sil-type
%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<T = A, U = 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. 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 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.
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 : $@thin A -> B -> C -> D -> E {
entry(%a : $A):
%foo_1 = function_ref @foo_1 : $@thin (B, A) -> C -> D -> E
%thunk = partial_apply %foo_1(%a) : $@thin (B, A) -> C -> D -> E
return %thunk : $B -> C -> D -> E
}
func @foo_1 : $@thin (B, A) -> C -> D -> E {
entry(%b : $B, %a : $A):
%foo_2 = function_ref @foo_2 : $@thin (C, B, A) -> D -> E
%thunk = partial_apply %foo_2(%b, %a) : $@thin (C, B, A) -> D -> E
return %thunk : $(B, A) -> C -> D -> E
}
func @foo_2 : $@thin (C, B, A) -> D -> E {
entry(%c : $C, %b : $B, %a : $A):
%foo_3 = function_ref @foo_3 : $@thin (D, C, B, A) -> E
%thunk = partial_apply %foo_3(%c, %b, %a) : $@thin (D, C, B, A) -> E
return %thunk : $(C, B, A) -> D -> E
}
func @foo_3 : $@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 : $@thin (Int, Builtin.ObjectPointer, *Int) -> Int {
entry(%y : $Int, %x_box : $Builtin.ObjectPointer, %x_address : $*Int):
// ... body of bar ...
}
func @foo : $@thin Int -> Int {
entry(%x : $Int):
// Create a box for the 'x' variable
%x_box = alloc_box $Int
store %x to %x_box#1 : $*Int
// Create the bar closure
%bar_uncurried = function_ref @bar : $(Int, Int) -> Int
%bar = partial_apply %bar_uncurried(%x_box#0, %x_box#1) \
: $(Int, Builtin.ObjectPointer, *Int) -> Int
// Apply it
%1 = integer_literal $Int, 1
%ret = apply %bar(%1) : $(Int) -> Int
// Clean up
release %bar : $(Int) -> Int
return %ret : $Int
}
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.metatype // %1 has type $T.metatype
Creates a reference to the metatype object for type T.
sil-instruction ::= 'value_metatype' sil-type ',' sil-operand %1 = value_metatype $T.metatype, %0 : $T // %0 must be a value or address of type $T // %1 will be of type $T.metatype
Obtains a reference to the dynamic metatype of the value %0.
sil-instruction ::= 'existential_metatype' sil-type ',' sil-operand %1 = existential_metatype $P.metatype, %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.metatype 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.
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 ::= '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 ::= '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 ::= '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 ::= '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.
These instructions construct 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
copy_addr [take] %2 to [initialization] %1 : $*AddressOnlyType
// Inject the tag.
inject_enum_addr %0 : $*AddressOnlyEnum, #AddressOnlyEnum.HasData
return
}
sil @init_without_data : $() -> AddressOnlyEnum {
// No data. We only need to inject the tag.
inject_enum_addr %0 : $*AddressOnlyEnum, #AddressOnlyEnum.NoData
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: a_dest, case #Foo.B: 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: a_dest, case #Foo.B: b_dest
a_dest:
%a = unchecked_take_enum_data_addr %foo : $*Foo<T>, #Foo.A
/* use %a */
b_dest:
%b = unchecked_take_enum_data_addr %foo : $*Foo<T>, #Foo.B
/* use %b */
}
sil-instruction ::= 'enum' sil-type ',' sil-decl-ref (',' sil-operand)?
%1 = enum $U, #U.EmptyCase
%1 = enum $U, #U.DataCase, %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 // $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 // $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 // $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 // $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.
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.
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. Applying destroy_addr to an
opaque existential container destroys the concrete value and deallocates any
buffers owned by the existential container.
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 and release-d.
sil-instruction ::= 'init_existential' sil-operand ',' sil-type %1 = init_existential %0 : $*P, $T // %0 must be of a $*P address type for non-class protocol or protocol // composition type P // $T must be a type that fulfills protocol(s) P // %1 will be 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 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 ::= 'upcast_existential' '[take]'? sil-operand
'to' sil-operand
upcast_existential %0 : $*protocol<P, Q> to %1 : $*P
// %0 must be the address of a non-class protocol or protocol composition
// type
// %1 must be the address of a non-class protocol or protocol composition
// type that is a supertype of %0
Initializes the memory referenced by the destination %1 with the value
contained in the existing existential container referenced by %0.
The [take] attribute may be applied to the instruction, in which case,
the source existential container is destroyed and ownership of the contained
value is taken by the destination. Without the [take] attribute, the
destination receives an independently-owned copy of the value.
sil-instruction ::= 'deinit_existential' sil-operand deinit_existential %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. deinit_existential is only valid for
existential containers that have been partially initialized by
init_existential but haven't had their contained value initialized.
A fully initialized existential must be destroyed with destroy_addr.
sil-instruction ::= 'project_existential' sil-operand 'to' sil-type %1 = project_existential %0 : $*P to $*@sil_self P // %0 must be of a $*P type for non-class protocol or protocol composition // type P // $*@sil_self P must be the address-of-Self type for one of the protocols %0 // conforms to // %1 will be of type $*@sil_self P
Obtains the address of the concrete value inside the
existential container referenced by %0. This pointer can be passed to
protocol instance methods obtained by protocol_method from the same
existential container. A method call on a protocol-type value in Swift:
protocol Foo {
func bar(x:Int)
}
var foo:Foo
// ... initialize foo
foo.bar(123)
compiles to this SIL sequence:
// ... initialize %foo %bar = protocol_method %foo : $*Foo, #Foo.bar!1 %foo_p = project_existential %foo : $*Foo %one_two_three = integer_literal $Int, 123 apply %bar(%one_two_three, %foo_p) : $(Int, Builtin.OpaquePointer) -> ()
It is undefined behavior for the address to be passed as the
"self" argument to a method value obtained by protocol_method from
a different existential container. It is also undefined behavior if the
OpaquePointer value is dereferenced, cast, or passed to a method after
the originating existential container has been mutated.
sil-instruction ::= 'open_existential' sil-operand 'to' sil-type %1 = open_existential %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 $*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.
sil-instruction ::= 'init_existential_ref' sil-operand ',' sil-type %1 = init_existential_ref %0 : $C, $P // %0 must be of class 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 ::= 'upcast_existential_ref' sil-operand 'to' sil-type %1 = upcast_existential_ref %0 : $protocol<P, Q> to $P // %0 must be of a class protocol or protocol composition type // $P must be a class protocol or protocol composition type that is a // supertype of %0's type
Converts a class existential container to a more general protocol or protocol composition type.
sil-instruction ::= 'project_existential_ref' sil-operand %1 = project_existential_ref %0 : $P // %0 must be of a class protocol or protocol composition type $P // $@sil_self P must be the Self type for one of the protocols %0 // conforms to // %1 will be of type $@sil_self P
Extracts the class instance reference from a class existential container.
This value can be passed to protocol instance methods obtained by
protocol_method from the same existential container. A method call on a
class-protocol-type value in Swift:
@class_protocol protocol Foo {
func bar(x:Int)
}
var foo:Foo
// ... initialize foo
foo.bar(123)
compiles to this SIL sequence:
// ... initialize %foo %bar = protocol_method %foo : $Foo, #Foo.bar!1 %foo_p = project_existential_ref %foo : $Foo %one_two_three = integer_literal $Int, 123 apply %bar(%one_two_three, %foo_p) : $(Int, Builtin.ObjCPointer) -> ()
It is undefined behavior for the Self-typed value to be passed as the
"self" argument to a method value obtained by protocol_method from
a different existential container. It is also undefined behavior if the
ObjCPointer value is dereferenced, cast, or passed to a method after the
originating existential container has been mutated.
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, class protocol composition, or a metatype of a protocol or protocol composition // $@opened P must be a unique archetype that refers to an opened // existential type P. // %1 will be of type $P
Extracts the class instance refernece 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.
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' sil-type %1 = pointer_to_address %0 : $Builtin.RawPointer to $*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.
sil-instruction ::= 'unchecked_ref_cast' sil-operand 'to' sil-type %1 = unchecked_ref_cast %0 : $C to $D // %0 must be of heap object reference type $C // $D must be a heap object reference type // %1 will be of type $D
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.
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.
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.ObjectPointer, or Builtin.ObjCPointer // %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.ObjectPointer, or Builtin.ObjCPointer // %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 ::= 'convert_function' sil-operand 'to' 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, with the following exceptions:
- The
cc,thin, andobjc_blockattributes cannot be changed. - A
@noreturnfunction may be converted to a non-@noreturntype and vice-versa.
sil-instruction ::= 'thick_to_objc_metatype' sil-operand 'to' sil-type %1 = thick_to_objc_metatype %0 : $@thick T.metatype to $@objc_metatype T.metatype // %0 must be of a thick metatype type $@thick T.metatype // The destination type must be the corresponding Objective-C metatype type // %1 will be of type $@objc_metatype T.metatype
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.metatype to $@thick T.metatype // %0 must be of an Objective-C metatype type $@objc_metatype T.metatype // The destination type must be the corresponding thick metatype type // %1 will be of type $@thick T.metatype
Converts an Objective-C class metatype to a thick metatype. T must
be of class, class protocol, or class protocol composition type.
sil-instruction ::= 'thin_to_thick_function' sil-operand 'to' sil-type %1 = thin_to_thick_function %0 : $@thin T -> U to $T -> U // %0 must be of a thin function type $@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 ::= 'is_nonnull' sil-operand %1 = is_nonnull %0 : $C // %0 must be of reference type $C // %1 will be of type Builtin.Int1
Checks whether a reference type value is null, returning 1 if the value is not null, or 0 if it is null.
Some user-level cast operations can fail and thus require runtime checking.
The unconditional_checked_cast instruction performs an unconditional checked cast; it is a runtime failure if the cast fails. The 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 conversion, causing a runtime failure if the conversion fails.
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
@noreturn 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. The
result of the apply instruction that invoked the current function will be
the operand of this return instruction. return does not retain or
release its operand or any other values.
sil-terminator ::= 'autorelease_return' sil-operand autorelease_return %0 : $T // $T must be the return type of the current function, which must be of // class type
Exits the current function and returns control to the calling function. The
result of the apply instruction that invoked the current function will be
the operand of this return instruction. The return value is autoreleased
into the active Objective-C autorelease pool using the "autoreleased return
value" optimization. The current function must use the @cc(objc_method)
calling convention.
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
// %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 the arguments of the chosen destination block.
sil-terminator ::= 'switch_int' sil-operand
(',' sil-switch-int-case)*
(',' sil-switch-default)?
sil-switch-int-case ::= 'case' int-literal ':' sil-identifier
sil-switch-default ::= 'default' sil-identifier
switch_int %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 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-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: label1, \
case #U.Bar: 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
is resilient, the default branch is required; if the enum type is
fragile, 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: nothing, \
case #Foo.OneInt: one_int, \
case #Foo.TwoInts: two_ints
nothing:
%zero = integer_literal 0 : $Int
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: label1, \
case #U.Bar: 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 is resilient, the default branch is required; if the
enum type is fragile, 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 type Builtin.ObjCPointer
// where $P contains the Swift.DynamicLookup protocol
// #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 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.
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
funtion application is the optimization flag: at -O0 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 -AssertConf 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.