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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\">$2</a>\n";
}
@x = map { s/^\d\d\d//; $_ } sort @x;
@y = map { s/^\d\d\d//; $_ } sort @y;
print @x, @y;
EOT
-->
<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:rspencer@x10sys.com">Reid Spencer</a></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="#anders-aa">-anders-aa</a></td><td>Andersen's Interprocedural Alias Analysis</td></tr>
<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (default AA impl)</td></tr>
<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
<tr><td><a href="#basicvn">-basicvn</a></td><td>Basic Value Numbering (default GVN impl)</td></tr>
<tr><td><a href="#callgraph">-callgraph</a></td><td>Print a call graph</td></tr>
<tr><td><a href="#callscc">-callscc</a></td><td>Print SCCs of the Call Graph</td></tr>
<tr><td><a href="#cfgscc">-cfgscc</a></td><td>Print SCCs of each function CFG</td></tr>
<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</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="#externalfnconstants">-externalfnconstants</a></td><td>Print external fn callsites passed constants</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="#gvn">-gvn</a></td><td>Global Value Numbering</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="#load-vn">-load-vn</a></td><td>Load Value Numbering</td></tr>
<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Construction</td></tr>
<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</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">-print</a></td><td>Print function to stderr</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 Call Graph to 'dot' file</td></tr>
<tr><td><a href="#print-cfg">-print-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
<tr><td><a href="#print-cfg-only">-print-cfg-only</a></td><td>Print CFG of function to 'dot' file (with no function bodies)</td></tr>
<tr><td><a href="#printm">-printm</a></td><td>Print module to stderr</td></tr>
<tr><td><a href="#printusedtypes">-printusedtypes</a></td><td>Find Used Types</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="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution 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="#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="#cee">-cee</a></td><td>Correlated Expression Elimination</td></tr>
<tr><td><a href="#condprop">-condprop</a></td><td>Conditional Propagation</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="#gcse">-gcse</a></td><td>Global Common Subexpression Elimination</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="#gvnpre">-gvnpre</a></td><td>Global Value Numbering/Partial Redundancy Elimination</td></tr>
<tr><td><a href="#indmemrem">-indmemrem</a></td><td>Indirect Malloc and Free Removal</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-block-profiling">-insert-block-profiling</a></td><td>Insert instrumentation for block profiling</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-function-profiling">-insert-function-profiling</a></td><td>Insert instrumentation for function profiling</td></tr>
<tr><td><a href="#insert-null-profiling-rs">-insert-null-profiling-rs</a></td><td>Measure profiling framework overhead</td></tr>
<tr><td><a href="#insert-rs-profiling-framework">-insert-rs-profiling-framework</a></td><td>Insert random sampling instrumentation framework</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="#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-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-index-split">-loop-index-split</a></td><td>Index Split Loops</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-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="#loopsimplify">-loopsimplify</a></td><td>Canonicalize natural loops</td></tr>
<tr><td><a href="#lower-packed">-lower-packed</a></td><td>lowers packed operations to operations on smaller packed datatypes</td></tr>
<tr><td><a href="#lowerallocs">-lowerallocs</a></td><td>Lower allocations from instructions to calls</td></tr>
<tr><td><a href="#lowergc">-lowergc</a></td><td>Lower GC intrinsics, for GCless code generators</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="#lowerselect">-lowerselect</a></td><td>Lower select instructions to branches</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="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
<tr><td><a href="#predsimplify">-predsimplify</a></td><td>Predicate Simplifier</td></tr>
<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
<tr><td><a href="#raiseallocs">-raiseallocs</a></td><td>Raise allocations from calls to instructions</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</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="#strip">-strip</a></td><td>Strip all 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="#emitbitcode">-emitbitcode</a></td><td>Bitcode Writer</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>
</table>
</div>
<!-- ======================================================================= -->
<div class="doc_section"> <a name="example">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">Exhaustive Alias Analysis Precision Evaluator</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="anders-aa">Andersen's Interprocedural Alias Analysis</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="basicaa">Basic Alias Analysis (default AA impl)</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="basiccg">Basic CallGraph Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="basicvn">Basic Value Numbering (default GVN impl)</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="callgraph">Print a call graph</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="callscc">Print SCCs of the Call Graph</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="cfgscc">Print SCCs of each function CFG</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="codegenprepare">Optimize for code generation</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="count-aa">Count Alias Analysis Query Responses</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="debug-aa">AA use debugger</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="domfrontier">Dominance Frontier Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="domtree">Dominator Tree Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="externalfnconstants">Print external fn callsites passed constants</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="globalsmodref-aa">Simple mod/ref analysis for globals</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="gvn">Global Value Numbering</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="instcount">Counts the various types of Instructions</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="intervals">Interval Partition Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="load-vn">Load Value Numbering</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loops">Natural Loop Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="memdep">Memory Dependence Analysis</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="no-aa">No Alias Analysis (always returns 'may' alias)</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="no-profile">No Profile Information</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="postdomfrontier">Post-Dominance Frontier Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="postdomtree">Post-Dominator Tree Construction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print">Print function to stderr</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="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 Call Graph to 'dot' file</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-cfg">Print CFG of function to 'dot' file</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="print-cfg-only">Print CFG of function to 'dot' file (with no function bodies)</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="printm">Print module to stderr</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="printusedtypes">Find Used Types</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="profile-loader">Load profile information from llvmprof.out</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="scalar-evolution">Scalar Evolution Analysis</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="targetdata">Target Data Layout</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_section"> <a name="transform">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">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="argpromotion">Promote 'by reference' arguments to scalars</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="block-placement">Profile Guided Basic Block Placement</a>
</div>
<div class="doc_text">
<p>This pass implements 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>
<p>The algorithm implemented here is basically "Algo1" from "Profile Guided
Code Positioning" by Pettis and Hansen, except that it uses basic block
counts instead of edge counts. This could be improved in many ways, but is
very simple for now.</p>
<p>Basically we "place" the entry block, then loop over all successors in a
DFO, placing the most frequently executed successor until we run out of
blocks. Did we mention that this was <b>extremely</b> simplistic? This is
also much slower than it could be. When it becomes important, this pass
will be rewritten to use a better algorithm, and then we can worry about
efficiency.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="break-crit-edges">Break critical edges in CFG</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="cee">Correlated Expression Elimination</a>
</div>
<div class="doc_text">
<p>Correlated Expression Elimination propagates information from conditional
branches to blocks dominated by destinations of the branch. It propagates
information from the condition check itself into the body of the branch,
allowing transformations like these for example:</p>
<blockquote><pre>
if (i == 7)
... 4*i; // constant propagation
M = i+1; N = j+1;
if (i == j)
X = M-N; // = M-M == 0;
</pre></blockquote>
<p>This is called Correlated Expression Elimination because we eliminate or
simplify expressions that are correlated with the direction of a branch. In
this way we use static information to give us some information about the
dynamic value of a variable.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="condprop">Conditional Propagation</a>
</div>
<div class="doc_text">
<p>This pass propagates information about conditional expressions through the
program, allowing it to eliminate conditional branches in some cases.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="constmerge">Merge Duplicate Global Constants</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="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">Dead Code Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="deadargelim">Dead Argument Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="deadtypeelim">Dead Type Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="die">Dead Instruction Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="dse">Dead Store Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="gcse">Global Common Subexpression Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="globaldce">Dead Global Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="globalopt">Global Variable Optimizer</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="gvnpre">Global Value Numbering/Partial Redundancy Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="indmemrem">Indirect Malloc and Free Removal</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="indvars">Canonicalize Induction Variables</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="inline">Function Integration/Inlining</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="insert-block-profiling">Insert instrumentation for block profiling</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="insert-edge-profiling">Insert instrumentation for edge profiling</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="insert-function-profiling">Insert instrumentation for function profiling</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="insert-null-profiling-rs">Measure profiling framework overhead</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="insert-rs-profiling-framework">Insert random sampling instrumentation framework</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="instcombine">Combine redundant instructions</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="internalize">Internalize Global Symbols</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="ipconstprop">Interprocedural constant propagation</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="ipsccp">Interprocedural Sparse Conditional Constant Propagation</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lcssa">Loop-Closed SSA Form Pass</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="licm">Loop Invariant Code Motion</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loop-extract">Extract loops into new functions</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loop-extract-single">Extract at most one loop into a new function</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loop-index-split">Index Split Loops</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loop-reduce">Loop Strength Reduction</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loop-rotate">Rotate Loops</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loop-unroll">Unroll loops</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loop-unswitch">Unswitch loops</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="loopsimplify">Canonicalize natural loops</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lower-packed">lowers packed operations to operations on smaller packed datatypes</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lowerallocs">Lower allocations from instructions to calls</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lowergc">Lower GC intrinsics, for GCless code generators</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lowerinvoke">Lower invoke and unwind, for unwindless code generators</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lowerselect">Lower select instructions to branches</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lowersetjmp">Lower Set Jump</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="lowerswitch">Lower SwitchInst's to branches</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="mem2reg">Promote Memory to Register</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="mergereturn">Unify function exit nodes</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="predsimplify">Predicate Simplifier</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="prune-eh">Remove unused exception handling info</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="raiseallocs">Raise allocations from calls to instructions</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="reassociate">Reassociate expressions</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="reg2mem">Demote all values to stack slots</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="scalarrepl">Scalar Replacement of Aggregates</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="sccp">Sparse Conditional Constant Propagation</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="simplify-libcalls">Simplify well-known library calls</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="simplifycfg">Simplify the CFG</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="strip">Strip all symbols from a module</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="tailcallelim">Tail Call Elimination</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="tailduplicate">Tail Duplication</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_section"> <a name="transform">Utility Passes</a></div>
<div class="doc_text">
<p>This section describes the LLVM Utility Passes.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="deadarghaX0r">Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="extract-blocks">Extract Basic Blocks From Module (for bugpoint use)</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="emitbitcode">Bitcode Writer</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="verify">Module Verifier</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="view-cfg">View CFG of function</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
<div class="doc_subsection">
<a name="view-cfg-only">View CFG of function (with no function bodies)</a>
</div>
<div class="doc_text">
<p>Yet to be written.</p>
</div>
<!-- *********************************************************************** -->
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