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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>LLVM's Analysis and Transform Passes</title>
<link rel="stylesheet" href="llvm.css" type="text/css">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<!--
If Passes.html is up to date, the following "one-liner" should print
an empty diff.
egrep -e '^<tr><td><a href="#.*">-.*</a></td><td>.*</td></tr>$' \
-e '^ <a name=".*">.*</a>$' < Passes.html >html; \
perl >help <<'EOT' && diff -u help html; rm -f help html
open HTML, "<Passes.html" or die "open: Passes.html: $!\n";
while (<HTML>) {
m:^<tr><td><a href="#(.*)">-.*</a></td><td>.*</td></tr>$: or next;
$order{$1} = sprintf("%03d", 1 + int %order);
}
open HELP, "../Release/bin/opt -help|" or die "open: opt -help: $!\n";
while (<HELP>) {
m:^ -([^ ]+) +- (.*)$: or next;
my $o = $order{$1};
$o = "000" unless defined $o;
push @x, "$o<tr><td><a href=\"#$1\">-$1</a></td><td>$2</td></tr>\n";
push @y, "$o <a name=\"$1\">-$1: $2</a>\n";
}
@x = map { s/^\d\d\d//; $_ } sort @x;
@y = map { s/^\d\d\d//; $_ } sort @y;
print @x, @y;
EOT
This (real) one-liner can also be helpful when converting comments to HTML:
perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print " <p>\n" if !$on && $_ =~ /\S/; print " </p>\n" if $on && $_ =~ /^\s*$/; print " $_\n"; $on = ($_ =~ /\S/); } print " </p>\n" if $on'
-->
<div class="doc_title">LLVM's Analysis and Transform Passes</div>
<ol>
<li><a href="#intro">Introduction</a></li>
<li><a href="#analyses">Analysis Passes</a>
<li><a href="#transforms">Transform Passes</a></li>
<li><a href="#utilities">Utility Passes</a></li>
</ol>
<div class="doc_author">
<p>Written by <a href="mailto:[email protected]">Reid Spencer</a>
and Gordon Henriksen</p>
</div>
<!-- ======================================================================= -->
<div class="doc_section"> <a name="intro">Introduction</a> </div>
<div class="doc_text">
<p>This document serves as a high level summary of the optimization features
that LLVM provides. Optimizations are implemented as Passes that traverse some
portion of a program to either collect information or transform the program.
The table below divides the passes that LLVM provides into three categories.
Analysis passes compute information that other passes can use or for debugging
or program visualization purposes. Transform passes can use (or invalidate)
the analysis passes. Transform passes all mutate the program in some way.
Utility passes provides some utility but don't otherwise fit categorization.
For example passes to extract functions to bitcode or write a module to
bitcode are neither analysis nor transform passes.
<p>The table below provides a quick summary of each pass and links to the more
complete pass description later in the document.</p>
</div>
<div class="doc_text" >
<table>
<tr><th colspan="2"><b>ANALYSIS PASSES</b></th></tr>
<tr><th>Option</th><th>Name</th></tr>
<tr><td><a href="#aa-eval">-aa-eval</a></td><td>Exhaustive Alias Analysis Precision Evaluator</td></tr>
<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (stateless AA impl)</td></tr>
<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
<tr><td><a href="#dot-callgraph">-dot-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
<tr><td><a href="#dot-cfg">-dot-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
<tr><td><a href="#dot-cfg-only">-dot-cfg-only</a></td><td>Print CFG of function to 'dot' file (with no function bodies)</td></tr>
<tr><td><a href="#dot-dom">-dot-dom</a></td><td>Print dominance tree of function to 'dot' file</td></tr>
<tr><td><a href="#dot-dom-only">-dot-dom-only</a></td><td>Print dominance tree of function to 'dot' file (with no function bodies)</td></tr>
<tr><td><a href="#dot-postdom">-dot-postdom</a></td><td>Print postdominance tree of function to 'dot' file</td></tr>
<tr><td><a href="#dot-postdom-only">-dot-postdom-only</a></td><td>Print postdominance tree of function to 'dot' file (with no function bodies)</td></tr>
<tr><td><a href="#globalsmodref-aa">-globalsmodref-aa</a></td><td>Simple mod/ref analysis for globals</td></tr>
<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
<tr><td><a href="#iv-users">-iv-users</a></td><td>Induction Variable Users</td></tr>
<tr><td><a href="#lazy-value-info">-lazy-value-info</a></td><td>Lazy Value Information Analysis</td></tr>
<tr><td><a href="#lda">-lda</a></td><td>Loop Dependence Analysis</td></tr>
<tr><td><a href="#libcall-aa">-libcall-aa</a></td><td>LibCall Alias Analysis</td></tr>
<tr><td><a href="#lint">-lint</a></td><td>Statically lint-checks LLVM IR</td></tr>
<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Information</td></tr>
<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
<tr><td><a href="#module-debuginfo">-module-debuginfo</a></td><td>Decodes module-level debug info</td></tr>
<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
<tr><td><a href="#postdomfrontier">-postdomfrontier</a></td><td>Post-Dominance Frontier Construction</td></tr>
<tr><td><a href="#postdomtree">-postdomtree</a></td><td>Post-Dominator Tree Construction</td></tr>
<tr><td><a href="#print-alias-sets">-print-alias-sets</a></td><td>Alias Set Printer</td></tr>
<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
<tr><td><a href="#print-cfg-sccs">-print-cfg-sccs</a></td><td>Print SCCs of each function CFG</td></tr>
<tr><td><a href="#print-dbginfo">-print-dbginfo</a></td><td>Print debug info in human readable form</td></tr>
<tr><td><a href="#print-dom-info">-print-dom-info</a></td><td>Dominator Info Printer</td></tr>
<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
<tr><td><a href="#print-used-types">-print-used-types</a></td><td>Find Used Types</td></tr>
<tr><td><a href="#profile-estimator">-profile-estimator</a></td><td>Estimate profiling information</td></tr>
<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
<tr><td><a href="#profile-verifier">-profile-verifier</a></td><td>Verify profiling information</td></tr>
<tr><td><a href="#regions">-regions</a></td><td>Detect single entry single exit regions</td></tr>
<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
<tr><td><a href="#scev-aa">-scev-aa</a></td><td>ScalarEvolution-based Alias Analysis</td></tr>
<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
<tr><th>Option</th><th>Name</th></tr>
<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
<tr><td><a href="#always-inline">-always-inline</a></td><td>Inliner for always_inline functions</td></tr>
<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
<tr><td><a href="#block-placement">-block-placement</a></td><td>Profile Guided Basic Block Placement</td></tr>
<tr><td><a href="#break-crit-edges">-break-crit-edges</a></td><td>Break critical edges in CFG</td></tr>
<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</td></tr>
<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
<tr><td><a href="#functionattrs">-functionattrs</a></td><td>Deduce function attributes</td></tr>
<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
<tr><td><a href="#insert-optimal-edge-profiling">-insert-optimal-edge-profiling</a></td><td>Insert optimal instrumentation for edge profiling</td></tr>
<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
<tr><td><a href="#ipsccp">-ipsccp</a></td><td>Interprocedural Sparse Conditional Constant Propagation</td></tr>
<tr><td><a href="#jump-threading">-jump-threading</a></td><td>Jump Threading</td></tr>
<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
<tr><td><a href="#licm">-licm</a></td><td>Loop Invariant Code Motion</td></tr>
<tr><td><a href="#loop-deletion">-loop-deletion</a></td><td>Delete dead loops</td></tr>
<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
<tr><td><a href="#loop-extract-single">-loop-extract-single</a></td><td>Extract at most one loop into a new function</td></tr>
<tr><td><a href="#loop-reduce">-loop-reduce</a></td><td>Loop Strength Reduction</td></tr>
<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
<tr><td><a href="#loop-simplify">-loop-simplify</a></td><td>Canonicalize natural loops</td></tr>
<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
<tr><td><a href="#loweratomic">-loweratomic</a></td><td>Lower atomic intrinsics to non-atomic form</td></tr>
<tr><td><a href="#lowerinvoke">-lowerinvoke</a></td><td>Lower invoke and unwind, for unwindless code generators</td></tr>
<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
<tr><td><a href="#mem2reg">-mem2reg</a></td><td>Promote Memory to Register</td></tr>
<tr><td><a href="#memcpyopt">-memcpyopt</a></td><td>MemCpy Optimization</td></tr>
<tr><td><a href="#mergefunc">-mergefunc</a></td><td>Merge Functions</td></tr>
<tr><td><a href="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
<tr><td><a href="#partial-inliner">-partial-inliner</a></td><td>Partial Inliner</td></tr>
<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
<tr><td><a href="#reg2mem">-reg2mem</a></td><td>Demote all values to stack slots</td></tr>
<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates (DT)</td></tr>
<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
<tr><td><a href="#sink">-sink</a></td><td>Code sinking</td></tr>
<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments to multiple ret values</td></tr>
<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
<tr><td><a href="#strip-dead-debug-info">-strip-dead-debug-info</a></td><td>Strip debug info for unused symbols</td></tr>
<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Strip Unused Function Prototypes</td></tr>
<tr><td><a href="#strip-debug-declare">-strip-debug-declare</a></td><td>Strip all llvm.dbg.declare intrinsics</td></tr>
<tr><td><a href="#strip-nondebug">-strip-nondebug</a></td><td>Strip all symbols, except dbg symbols, from a module</td></tr>
<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
<tr><th>Option</th><th>Name</th></tr>
<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
<tr><td><a href="#extract-blocks">-extract-blocks</a></td><td>Extract Basic Blocks From Module (for bugpoint use)</td></tr>
<tr><td><a href="#instnamer">-instnamer</a></td><td>Assign names to anonymous instructions</td></tr>
<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
<tr><td><a href="#view-cfg-only">-view-cfg-only</a></td><td>View CFG of function (with no function bodies)</td></tr>
<tr><td><a href="#view-dom">-view-dom</a></td><td>View dominance tree of function</td></tr>
<tr><td><a href="#view-dom-only">-view-dom-only</a></td><td>View dominance tree of function (with no function bodies)</td></tr>
<tr><td><a href="#view-postdom">-view-postdom</a></td><td>View postdominance tree of function</td></tr>
<tr><td><a href="#view-postdom-only">-view-postdom-only</a></td><td>View postdominance tree of function (with no function bodies)</td></tr>
</table>
</div>
<!-- ======================================================================= -->
<div class="doc_section"> <a name="analyses">Analysis Passes</a></div>
<div class="doc_text">
<p>This section describes the LLVM Analysis Passes.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="aa-eval">-aa-eval: Exhaustive Alias Analysis Precision Evaluator</a>
</div>
<div class="doc_text">
<p>This is a simple N^2 alias analysis accuracy evaluator.
Basically, for each function in the program, it simply queries to see how the
alias analysis implementation answers alias queries between each pair of
pointers in the function.</p>
<p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
Spadini, and Wojciech Stryjewski.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="basicaa">-basicaa: Basic Alias Analysis (stateless AA impl)</a>
</div>
<div class="doc_text">
<p>
This is the default implementation of the Alias Analysis interface
that simply implements a few identities (two different globals cannot alias,
etc), but otherwise does no analysis.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="basiccg">-basiccg: Basic CallGraph Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="count-aa">-count-aa: Count Alias Analysis Query Responses</a>
</div>
<div class="doc_text">
<p>
A pass which can be used to count how many alias queries
are being made and how the alias analysis implementation being used responds.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="debug-aa">-debug-aa: AA use debugger</a>
</div>
<div class="doc_text">
<p>
This simple pass checks alias analysis users to ensure that if they
create a new value, they do not query AA without informing it of the value.
It acts as a shim over any other AA pass you want.
</p>
<p>
Yes keeping track of every value in the program is expensive, but this is
a debugging pass.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="domfrontier">-domfrontier: Dominance Frontier Construction</a>
</div>
<div class="doc_text">
<p>
This pass is a simple dominator construction algorithm for finding forward
dominator frontiers.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="domtree">-domtree: Dominator Tree Construction</a>
</div>
<div class="doc_text">
<p>
This pass is a simple dominator construction algorithm for finding forward
dominators.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dot-callgraph">-dot-callgraph: Print Call Graph to 'dot' file</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the call graph into a
<code>.dot</code> graph. This graph can then be processed with the "dot" tool
to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dot-cfg">-dot-cfg: Print CFG of function to 'dot' file</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the control flow graph
into a <code>.dot</code> graph. This graph can then be processed with the
"dot" tool to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dot-cfg-only">-dot-cfg-only: Print CFG of function to 'dot' file (with no function bodies)</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the control flow graph
into a <code>.dot</code> graph, omitting the function bodies. This graph can
then be processed with the "dot" tool to convert it to postscript or some
other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dot-dom">-dot-dom: Print dominance tree of function to 'dot' file</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the dominator tree
into a <code>.dot</code> graph. This graph can then be processed with the
"dot" tool to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dot-dom-only">-dot-dom-only: Print dominance tree of function to 'dot' file (with no function bodies)</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the dominator tree
into a <code>.dot</code> graph, omitting the function bodies. This graph can
then be processed with the "dot" tool to convert it to postscript or some
other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dot-postdom">-dot-postdom: Print postdominance tree of function to 'dot' file</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the post dominator tree
into a <code>.dot</code> graph. This graph can then be processed with the
"dot" tool to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dot-postdom-only">-dot-postdom-only: Print postdominance tree of function to 'dot' file (with no function bodies)</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the post dominator tree
into a <code>.dot</code> graph, omitting the function bodies. This graph can
then be processed with the "dot" tool to convert it to postscript or some
other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="globalsmodref-aa">-globalsmodref-aa: Simple mod/ref analysis for globals</a>
</div>
<div class="doc_text">
<p>
This simple pass provides alias and mod/ref information for global values
that do not have their address taken, and keeps track of whether functions
read or write memory (are "pure"). For this simple (but very common) case,
we can provide pretty accurate and useful information.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="instcount">-instcount: Counts the various types of Instructions</a>
</div>
<div class="doc_text">
<p>
This pass collects the count of all instructions and reports them
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="intervals">-intervals: Interval Partition Construction</a>
</div>
<div class="doc_text">
<p>
This analysis calculates and represents the interval partition of a function,
or a preexisting interval partition.
</p>
<p>
In this way, the interval partition may be used to reduce a flow graph down
to its degenerate single node interval partition (unless it is irreducible).
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="iv-users">-iv-users: Induction Variable Users</a>
</div>
<div class="doc_text">
<p>Bookkeeping for "interesting" users of expressions computed from
induction variables.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lazy-value-info">-lazy-value-info: Lazy Value Information Analysis</a>
</div>
<div class="doc_text">
<p>Interface for lazy computation of value constraint information.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lda">-lda: Loop Dependence Analysis</a>
</div>
<div class="doc_text">
<p>Loop dependence analysis framework, which is used to detect dependences in
memory accesses in loops.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="libcall-aa">-libcall-aa: LibCall Alias Analysis</a>
</div>
<div class="doc_text">
<p>LibCall Alias Analysis.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lint">-lint: Statically lint-checks LLVM IR</a>
</div>
<div class="doc_text">
<p>This pass statically checks for common and easily-identified constructs
which produce undefined or likely unintended behavior in LLVM IR.</p>
<p>It is not a guarantee of correctness, in two ways. First, it isn't
comprehensive. There are checks which could be done statically which are
not yet implemented. Some of these are indicated by TODO comments, but
those aren't comprehensive either. Second, many conditions cannot be
checked statically. This pass does no dynamic instrumentation, so it
can't check for all possible problems.</p>
<p>Another limitation is that it assumes all code will be executed. A store
through a null pointer in a basic block which is never reached is harmless,
but this pass will warn about it anyway.</p>
<p>Optimization passes may make conditions that this pass checks for more or
less obvious. If an optimization pass appears to be introducing a warning,
it may be that the optimization pass is merely exposing an existing
condition in the code.</p>
<p>This code may be run before instcombine. In many cases, instcombine checks
for the same kinds of things and turns instructions with undefined behavior
into unreachable (or equivalent). Because of this, this pass makes some
effort to look through bitcasts and so on.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loops">-loops: Natural Loop Information</a>
</div>
<div class="doc_text">
<p>
This analysis is used to identify natural loops and determine the loop depth
of various nodes of the CFG. Note that the loops identified may actually be
several natural loops that share the same header node... not just a single
natural loop.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="memdep">-memdep: Memory Dependence Analysis</a>
</div>
<div class="doc_text">
<p>
An analysis that determines, for a given memory operation, what preceding
memory operations it depends on. It builds on alias analysis information, and
tries to provide a lazy, caching interface to a common kind of alias
information query.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="module-debuginfo">-module-debuginfo: Decodes module-level debug info</a>
</div>
<div class="doc_text">
<p>This pass decodes the debug info metadata in a module and prints in a
(sufficiently-prepared-) human-readable form.
For example, run this pass from opt along with the -analyze option, and
it'll print to standard output.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="no-aa">-no-aa: No Alias Analysis (always returns 'may' alias)</a>
</div>
<div class="doc_text">
<p>
Always returns "I don't know" for alias queries. NoAA is unlike other alias
analysis implementations, in that it does not chain to a previous analysis. As
such it doesn't follow many of the rules that other alias analyses must.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="no-profile">-no-profile: No Profile Information</a>
</div>
<div class="doc_text">
<p>
The default "no profile" implementation of the abstract
<code>ProfileInfo</code> interface.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="postdomfrontier">-postdomfrontier: Post-Dominance Frontier Construction</a>
</div>
<div class="doc_text">
<p>
This pass is a simple post-dominator construction algorithm for finding
post-dominator frontiers.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="postdomtree">-postdomtree: Post-Dominator Tree Construction</a>
</div>
<div class="doc_text">
<p>
This pass is a simple post-dominator construction algorithm for finding
post-dominators.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-alias-sets">-print-alias-sets: Alias Set Printer</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-callgraph">-print-callgraph: Print a call graph</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the call graph to
standard error in a human-readable form.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-callgraph-sccs">-print-callgraph-sccs: Print SCCs of the Call Graph</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the SCCs of the call
graph to standard error in a human-readable form.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-cfg-sccs">-print-cfg-sccs: Print SCCs of each function CFG</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints the SCCs of each
function CFG to standard error in a human-readable form.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-dbginfo">-print-dbginfo: Print debug info in human readable form</a>
</div>
<div class="doc_text">
<p>Pass that prints instructions, and associated debug info:</p>
<ul>
<li>source/line/col information</li>
<li>original variable name</li>
<li>original type name</li>
</ul>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-dom-info">-print-dom-info: Dominator Info Printer</a>
</div>
<div class="doc_text">
<p>Dominator Info Printer.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-externalfnconstants">-print-externalfnconstants: Print external fn callsites passed constants</a>
</div>
<div class="doc_text">
<p>
This pass, only available in <code>opt</code>, prints out call sites to
external functions that are called with constant arguments. This can be
useful when looking for standard library functions we should constant fold
or handle in alias analyses.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-function">-print-function: Print function to stderr</a>
</div>
<div class="doc_text">
<p>
The <code>PrintFunctionPass</code> class is designed to be pipelined with
other <code>FunctionPass</code>es, and prints out the functions of the module
as they are processed.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-module">-print-module: Print module to stderr</a>
</div>
<div class="doc_text">
<p>
This pass simply prints out the entire module when it is executed.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-used-types">-print-used-types: Find Used Types</a>
</div>
<div class="doc_text">
<p>
This pass is used to seek out all of the types in use by the program. Note
that this analysis explicitly does not include types only used by the symbol
table.
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="profile-estimator">-profile-estimator: Estimate profiling information</a>
</div>
<div class="doc_text">
<p>Profiling information that estimates the profiling information
in a very crude and unimaginative way.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="profile-loader">-profile-loader: Load profile information from llvmprof.out</a>
</div>
<div class="doc_text">
<p>
A concrete implementation of profiling information that loads the information
from a profile dump file.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="profile-verifier">-profile-verifier: Verify profiling information</a>
</div>
<div class="doc_text">
<p>Pass that checks profiling information for plausibility.</p>
</div>
<div class="doc_subsection">
<a name="regions">-regions: Detect single entry single exit regions</a>
</div>
<div class="doc_text">
<p>
The <code>RegionInfo</code> pass detects single entry single exit regions in a
function, where a region is defined as any subgraph that is connected to the
remaining graph at only two spots. Furthermore, an hierarchical region tree is
built.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="scalar-evolution">-scalar-evolution: Scalar Evolution Analysis</a>
</div>
<div class="doc_text">
<p>
The <code>ScalarEvolution</code> analysis can be used to analyze and
catagorize scalar expressions in loops. It specializes in recognizing general
induction variables, representing them with the abstract and opaque
<code>SCEV</code> class. Given this analysis, trip counts of loops and other
important properties can be obtained.
</p>
<p>
This analysis is primarily useful for induction variable substitution and
strength reduction.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="scev-aa">-scev-aa: ScalarEvolution-based Alias Analysis</a>
</div>
<div class="doc_text">
<p>Simple alias analysis implemented in terms of ScalarEvolution queries.
This differs from traditional loop dependence analysis in that it tests
for dependencies within a single iteration of a loop, rather than
dependencies between different iterations.
ScalarEvolution has a more complete understanding of pointer arithmetic
than BasicAliasAnalysis' collection of ad-hoc analyses.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="targetdata">-targetdata: Target Data Layout</a>
</div>
<div class="doc_text">
<p>Provides other passes access to information on how the size and alignment
required by the the target ABI for various data types.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_section"> <a name="transforms">Transform Passes</a></div>
<div class="doc_text">
<p>This section describes the LLVM Transform Passes.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="adce">-adce: Aggressive Dead Code Elimination</a>
</div>
<div class="doc_text">
<p>ADCE aggressively tries to eliminate code. This pass is similar to
<a href="#dce">DCE</a> but it assumes that values are dead until proven
otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
the liveness of values.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="always-inline">-always-inline: Inliner for always_inline functions</a>
</div>
<div class="doc_text">
<p>A custom inliner that handles only functions that are marked as
"always inline".</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="argpromotion">-argpromotion: Promote 'by reference' arguments to scalars</a>
</div>
<div class="doc_text">
<p>
This pass promotes "by reference" arguments to be "by value" arguments. In
practice, this means looking for internal functions that have pointer
arguments. If it can prove, through the use of alias analysis, that an
argument is *only* loaded, then it can pass the value into the function
instead of the address of the value. This can cause recursive simplification
of code and lead to the elimination of allocas (especially in C++ template
code like the STL).
</p>
<p>
This pass also handles aggregate arguments that are passed into a function,
scalarizing them if the elements of the aggregate are only loaded. Note that
it refuses to scalarize aggregates which would require passing in more than
three operands to the function, because passing thousands of operands for a
large array or structure is unprofitable!
</p>
<p>
Note that this transformation could also be done for arguments that are only
stored to (returning the value instead), but does not currently. This case
would be best handled when and if LLVM starts supporting multiple return
values from functions.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="block-placement">-block-placement: Profile Guided Basic Block Placement</a>
</div>
<div class="doc_text">
<p>This pass is a very simple profile guided basic block placement algorithm.
The idea is to put frequently executed blocks together at the start of the
function and hopefully increase the number of fall-through conditional
branches. If there is no profile information for a particular function, this
pass basically orders blocks in depth-first order.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="break-crit-edges">-break-crit-edges: Break critical edges in CFG</a>
</div>
<div class="doc_text">
<p>
Break all of the critical edges in the CFG by inserting a dummy basic block.
It may be "required" by passes that cannot deal with critical edges. This
transformation obviously invalidates the CFG, but can update forward dominator
(set, immediate dominators, tree, and frontier) information.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="codegenprepare">-codegenprepare: Optimize for code generation</a>
</div>
<div class="doc_text">
This pass munges the code in the input function to better prepare it for
SelectionDAG-based code generation. This works around limitations in it's
basic-block-at-a-time approach. It should eventually be removed.
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="constmerge">-constmerge: Merge Duplicate Global Constants</a>
</div>
<div class="doc_text">
<p>
Merges duplicate global constants together into a single constant that is
shared. This is useful because some passes (ie TraceValues) insert a lot of
string constants into the program, regardless of whether or not an existing
string is available.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="constprop">-constprop: Simple constant propagation</a>
</div>
<div class="doc_text">
<p>This file implements constant propagation and merging. It looks for
instructions involving only constant operands and replaces them with a
constant value instead of an instruction. For example:</p>
<blockquote><pre>add i32 1, 2</pre></blockquote>
<p>becomes</p>
<blockquote><pre>i32 3</pre></blockquote>
<p>NOTE: this pass has a habit of making definitions be dead. It is a good
idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
sometime after running this pass.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dce">-dce: Dead Code Elimination</a>
</div>
<div class="doc_text">
<p>
Dead code elimination is similar to <a href="#die">dead instruction
elimination</a>, but it rechecks instructions that were used by removed
instructions to see if they are newly dead.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="deadargelim">-deadargelim: Dead Argument Elimination</a>
</div>
<div class="doc_text">
<p>
This pass deletes dead arguments from internal functions. Dead argument
elimination removes arguments which are directly dead, as well as arguments
only passed into function calls as dead arguments of other functions. This
pass also deletes dead arguments in a similar way.
</p>
<p>
This pass is often useful as a cleanup pass to run after aggressive
interprocedural passes, which add possibly-dead arguments.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="deadtypeelim">-deadtypeelim: Dead Type Elimination</a>
</div>
<div class="doc_text">
<p>
This pass is used to cleanup the output of GCC. It eliminate names for types
that are unused in the entire translation unit, using the <a
href="#findusedtypes">find used types</a> pass.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="die">-die: Dead Instruction Elimination</a>
</div>
<div class="doc_text">
<p>
Dead instruction elimination performs a single pass over the function,
removing instructions that are obviously dead.
</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dse">-dse: Dead Store Elimination</a>
</div>
<div class="doc_text">
<p>
A trivial dead store elimination that only considers basic-block local
redundant stores.
</p>
</div>
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<div class="doc_subsection">
<a name="functionattrs">-functionattrs: Deduce function attributes</a>
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<p>A simple interprocedural pass which walks the call-graph, looking for
functions which do not access or only read non-local memory, and marking them
readnone/readonly. In addition, it marks function arguments (of pointer type)
'nocapture' if a call to the function does not create any copies of the pointer
value that outlive the call. This more or less means that the pointer is only
dereferenced, and not returned from the function or stored in a global.
This pass is implemented as a bottom-up traversal of the call-graph.
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<a name="globaldce">-globaldce: Dead Global Elimination</a>
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<p>
This transform is designed to eliminate unreachable internal globals from the
program. It uses an aggressive algorithm, searching out globals that are
known to be alive. After it finds all of the globals which are needed, it
deletes whatever is left over. This allows it to delete recursive chunks of
the program which are unreachable.
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<a name="globalopt">-globalopt: Global Variable Optimizer</a>
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<p>
This pass transforms simple global variables that never have their address
taken. If obviously true, it marks read/write globals as constant, deletes
variables only stored to, etc.
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<a name="gvn">-gvn: Global Value Numbering</a>
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<p>
This pass performs global value numbering to eliminate fully and partially
redundant instructions. It also performs redundant load elimination.
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