Gitiles
Code Review Sign In
gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 834b93b51de05fba014c63f6d05baeb0e80975dd / . / docs / Passes.html
blob: b7f70b91cbf30a606786871e5a0927ece07cc148 [file] [log] [blame]
NAKAMURA Takumib5f74912011-04-21 01:32:19 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2 "http://www.w3.org/TR/html4/strict.dtd">
3<html>
4<head>
5 <title>LLVM's Analysis and Transform Passes</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]8</head>
9<body>
10
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]11<!--
12
13If Passes.html is up to date, the following "one-liner" should print
14an empty diff.
15
16egrep -e '^<tr><td><a href="#.*">-.*</a></td><td>.*</td></tr>$' \
17 -e '^ <a name=".*">.*</a>$' < Passes.html >html; \
18perl >help <<'EOT' && diff -u help html; rm -f help html
19open HTML, "<Passes.html" or die "open: Passes.html: $!\n";
20while (<HTML>) {
21 m:^<tr><td><a href="#(.*)">-.*</a></td><td>.*</td></tr>$: or next;
22 $order{$1} = sprintf("%03d", 1 + int %order);
23}
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]24open HELP, "../Release/bin/opt -help|" or die "open: opt -help: $!\n";
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]25while (<HELP>) {
26 m:^ -([^ ]+) +- (.*)$: or next;
27 my $o = $order{$1};
28 $o = "000" unless defined $o;
29 push @x, "$o<tr><td><a href=\"#$1\">-$1</a></td><td>$2</td></tr>\n";
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]30 push @y, "$o <a name=\"$1\">-$1: $2</a>\n";
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]31}
32@x = map { s/^\d\d\d//; $_ } sort @x;
33@y = map { s/^\d\d\d//; $_ } sort @y;
34print @x, @y;
35EOT
36
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]37This (real) one-liner can also be helpful when converting comments to HTML:
38
39perl -e '$/ = 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'
40
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]41 -->
42
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]43<h1>LLVM's Analysis and Transform Passes</h1>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]44
45<ol>
46 <li><a href="#intro">Introduction</a></li>
47 <li><a href="#analyses">Analysis Passes</a>
48 <li><a href="#transforms">Transform Passes</a></li>
49 <li><a href="#utilities">Utility Passes</a></li>
50</ol>
51
52<div class="doc_author">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]53 <p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
54 and Gordon Henriksen</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]55</div>
56
57<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]58<h2><a name="intro">Introduction</a></h2>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]59<div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]60 <p>This document serves as a high level summary of the optimization features
61 that LLVM provides. Optimizations are implemented as Passes that traverse some
62 portion of a program to either collect information or transform the program.
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]63 The table below divides the passes that LLVM provides into three categories.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]64 Analysis passes compute information that other passes can use or for debugging
65 or program visualization purposes. Transform passes can use (or invalidate)
66 the analysis passes. Transform passes all mutate the program in some way.
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]67 Utility passes provides some utility but don't otherwise fit categorization.
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]68 For example passes to extract functions to bitcode or write a module to
69 bitcode are neither analysis nor transform passes.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]70 <p>The table below provides a quick summary of each pass and links to the more
71 complete pass description later in the document.</p>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]72
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]73<table>
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]74<tr><th colspan="2"><b>ANALYSIS PASSES</b></th></tr>
75<tr><th>Option</th><th>Name</th></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]76<tr><td><a href="#aa-eval">-aa-eval</a></td><td>Exhaustive Alias Analysis Precision Evaluator</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]77<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (stateless AA impl)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]78<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]79<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
80<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
81<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]82<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]83<tr><td><a href="#dot-callgraph">-dot-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
84<tr><td><a href="#dot-cfg">-dot-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
85<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>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]86<tr><td><a href="#dot-dom">-dot-dom</a></td><td>Print dominance tree of function to 'dot' file</td></tr>
87<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>
88<tr><td><a href="#dot-postdom">-dot-postdom</a></td><td>Print postdominance tree of function to 'dot' file</td></tr>
89<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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]90<tr><td><a href="#globalsmodref-aa">-globalsmodref-aa</a></td><td>Simple mod/ref analysis for globals</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]91<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
92<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]93<tr><td><a href="#iv-users">-iv-users</a></td><td>Induction Variable Users</td></tr>
94<tr><td><a href="#lazy-value-info">-lazy-value-info</a></td><td>Lazy Value Information Analysis</td></tr>
95<tr><td><a href="#lda">-lda</a></td><td>Loop Dependence Analysis</td></tr>
96<tr><td><a href="#libcall-aa">-libcall-aa</a></td><td>LibCall Alias Analysis</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]97<tr><td><a href="#lint">-lint</a></td><td>Statically lint-checks LLVM IR</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]98<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Information</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]99<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]100<tr><td><a href="#module-debuginfo">-module-debuginfo</a></td><td>Decodes module-level debug info</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]101<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
102<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
103<tr><td><a href="#postdomfrontier">-postdomfrontier</a></td><td>Post-Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]104<tr><td><a href="#postdomtree">-postdomtree</a></td><td>Post-Dominator Tree Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]105<tr><td><a href="#print-alias-sets">-print-alias-sets</a></td><td>Alias Set Printer</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]106<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
107<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
108<tr><td><a href="#print-cfg-sccs">-print-cfg-sccs</a></td><td>Print SCCs of each function CFG</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]109<tr><td><a href="#print-dbginfo">-print-dbginfo</a></td><td>Print debug info in human readable form</td></tr>
110<tr><td><a href="#print-dom-info">-print-dom-info</a></td><td>Dominator Info Printer</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]111<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
112<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
113<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
114<tr><td><a href="#print-used-types">-print-used-types</a></td><td>Find Used Types</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]115<tr><td><a href="#profile-estimator">-profile-estimator</a></td><td>Estimate profiling information</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]116<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]117<tr><td><a href="#profile-verifier">-profile-verifier</a></td><td>Verify profiling information</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]118<tr><td><a href="#regions">-regions</a></td><td>Detect single entry single exit regions</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]119<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]120<tr><td><a href="#scev-aa">-scev-aa</a></td><td>ScalarEvolution-based Alias Analysis</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]121<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
122
123
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]124<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
125<tr><th>Option</th><th>Name</th></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]126<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]127<tr><td><a href="#always-inline">-always-inline</a></td><td>Inliner for always_inline functions</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]128<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
129<tr><td><a href="#block-placement">-block-placement</a></td><td>Profile Guided Basic Block Placement</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]130<tr><td><a href="#break-crit-edges">-break-crit-edges</a></td><td>Break critical edges in CFG</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]131<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]132<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
133<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
134<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
135<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
136<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
137<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
138<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]139<tr><td><a href="#functionattrs">-functionattrs</a></td><td>Deduce function attributes</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]140<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
141<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]142<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]143<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
144<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]145<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]146<tr><td><a href="#insert-optimal-edge-profiling">-insert-optimal-edge-profiling</a></td><td>Insert optimal instrumentation for edge profiling</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]147<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
148<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
149<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
150<tr><td><a href="#ipsccp">-ipsccp</a></td><td>Interprocedural Sparse Conditional Constant Propagation</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]151<tr><td><a href="#jump-threading">-jump-threading</a></td><td>Jump Threading</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]152<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
153<tr><td><a href="#licm">-licm</a></td><td>Loop Invariant Code Motion</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]154<tr><td><a href="#loop-deletion">-loop-deletion</a></td><td>Delete dead loops</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]155<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
156<tr><td><a href="#loop-extract-single">-loop-extract-single</a></td><td>Extract at most one loop into a new function</td></tr>
157<tr><td><a href="#loop-reduce">-loop-reduce</a></td><td>Loop Strength Reduction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]158<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]159<tr><td><a href="#loop-simplify">-loop-simplify</a></td><td>Canonicalize natural loops</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]160<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
161<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]162<tr><td><a href="#loweratomic">-loweratomic</a></td><td>Lower atomic intrinsics to non-atomic form</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]163<tr><td><a href="#lowerinvoke">-lowerinvoke</a></td><td>Lower invoke and unwind, for unwindless code generators</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]164<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
165<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
166<tr><td><a href="#mem2reg">-mem2reg</a></td><td>Promote Memory to Register</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]167<tr><td><a href="#memcpyopt">-memcpyopt</a></td><td>MemCpy Optimization</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]168<tr><td><a href="#mergefunc">-mergefunc</a></td><td>Merge Functions</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]169<tr><td><a href="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]170<tr><td><a href="#partial-inliner">-partial-inliner</a></td><td>Partial Inliner</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]171<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]172<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
173<tr><td><a href="#reg2mem">-reg2mem</a></td><td>Demote all values to stack slots</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]174<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates (DT)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]175<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
176<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
177<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]178<tr><td><a href="#sink">-sink</a></td><td>Code sinking</td></tr>
179<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments to multiple ret values</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]180<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]181<tr><td><a href="#strip-dead-debug-info">-strip-dead-debug-info</a></td><td>Strip debug info for unused symbols</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]182<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Strip Unused Function Prototypes</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]183<tr><td><a href="#strip-debug-declare">-strip-debug-declare</a></td><td>Strip all llvm.dbg.declare intrinsics</td></tr>
184<tr><td><a href="#strip-nondebug">-strip-nondebug</a></td><td>Strip all symbols, except dbg symbols, from a module</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]185<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
186<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]187
188
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]189<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
190<tr><th>Option</th><th>Name</th></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]191<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
192<tr><td><a href="#extract-blocks">-extract-blocks</a></td><td>Extract Basic Blocks From Module (for bugpoint use)</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]193<tr><td><a href="#instnamer">-instnamer</a></td><td>Assign names to anonymous instructions</td></tr>
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]194<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]195<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]196<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
197<tr><td><a href="#view-cfg-only">-view-cfg-only</a></td><td>View CFG of function (with no function bodies)</td></tr>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]198<tr><td><a href="#view-dom">-view-dom</a></td><td>View dominance tree of function</td></tr>
199<tr><td><a href="#view-dom-only">-view-dom-only</a></td><td>View dominance tree of function (with no function bodies)</td></tr>
200<tr><td><a href="#view-postdom">-view-postdom</a></td><td>View postdominance tree of function</td></tr>
201<tr><td><a href="#view-postdom-only">-view-postdom-only</a></td><td>View postdominance tree of function (with no function bodies)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]202</table>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]203
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]204</div>
205
206<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]207<h2><a name="analyses">Analysis Passes</a></h2>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]208<div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]209 <p>This section describes the LLVM Analysis Passes.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]210
211<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]212<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]213 <a name="aa-eval">-aa-eval: Exhaustive Alias Analysis Precision Evaluator</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]214</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]215<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]216 <p>This is a simple N^2 alias analysis accuracy evaluator.
217 Basically, for each function in the program, it simply queries to see how the
218 alias analysis implementation answers alias queries between each pair of
219 pointers in the function.</p>
220
221 <p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
222 Spadini, and Wojciech Stryjewski.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]223</div>
224
225<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]226<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]227 <a name="basicaa">-basicaa: Basic Alias Analysis (stateless AA impl)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]228</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]229<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]230 <p>
231 This is the default implementation of the Alias Analysis interface
232 that simply implements a few identities (two different globals cannot alias,
233 etc), but otherwise does no analysis.
234 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]235</div>
236
237<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]238<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]239 <a name="basiccg">-basiccg: Basic CallGraph Construction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]240</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]241<div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]242 <p>Yet to be written.</p>
243</div>
244
245<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]246<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]247 <a name="count-aa">-count-aa: Count Alias Analysis Query Responses</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]248</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]249<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]250 <p>
251 A pass which can be used to count how many alias queries
252 are being made and how the alias analysis implementation being used responds.
253 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]254</div>
255
256<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]257<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]258 <a name="debug-aa">-debug-aa: AA use debugger</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]259</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]260<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]261 <p>
262 This simple pass checks alias analysis users to ensure that if they
263 create a new value, they do not query AA without informing it of the value.
264 It acts as a shim over any other AA pass you want.
265 </p>
266
267 <p>
268 Yes keeping track of every value in the program is expensive, but this is
269 a debugging pass.
270 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]271</div>
272
273<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]274<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]275 <a name="domfrontier">-domfrontier: Dominance Frontier Construction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]276</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]277<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]278 <p>
279 This pass is a simple dominator construction algorithm for finding forward
280 dominator frontiers.
281 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]282</div>
283
284<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]285<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]286 <a name="domtree">-domtree: Dominator Tree Construction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]287</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]288<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]289 <p>
290 This pass is a simple dominator construction algorithm for finding forward
291 dominators.
292 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]293</div>
294
295<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]296<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]297 <a name="dot-callgraph">-dot-callgraph: Print Call Graph to 'dot' file</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]298</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]299<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]300 <p>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]301 This pass, only available in <code>opt</code>, prints the call graph into a
302 <code>.dot</code> graph. This graph can then be processed with the "dot" tool
303 to convert it to postscript or some other suitable format.
304 </p>
305</div>
306
307<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]308<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]309 <a name="dot-cfg">-dot-cfg: Print CFG of function to 'dot' file</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]310</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]311<div>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]312 <p>
313 This pass, only available in <code>opt</code>, prints the control flow graph
314 into a <code>.dot</code> graph. This graph can then be processed with the
315 "dot" tool to convert it to postscript or some other suitable format.
316 </p>
317</div>
318
319<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]320<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]321 <a name="dot-cfg-only">-dot-cfg-only: Print CFG of function to 'dot' file (with no function bodies)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]322</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]323<div>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]324 <p>
325 This pass, only available in <code>opt</code>, prints the control flow graph
326 into a <code>.dot</code> graph, omitting the function bodies. This graph can
327 then be processed with the "dot" tool to convert it to postscript or some
328 other suitable format.
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]329 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]330</div>
331
332<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]333<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]334 <a name="dot-dom">-dot-dom: Print dominance tree of function to 'dot' file</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]335</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]336<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]337 <p>
338 This pass, only available in <code>opt</code>, prints the dominator tree
339 into a <code>.dot</code> graph. This graph can then be processed with the
340 "dot" tool to convert it to postscript or some other suitable format.
341 </p>
342</div>
343
344<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]345<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]346 <a name="dot-dom-only">-dot-dom-only: Print dominance tree of function to 'dot' file (with no function bodies)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]347</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]348<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]349 <p>
350 This pass, only available in <code>opt</code>, prints the dominator tree
351 into a <code>.dot</code> graph, omitting the function bodies. This graph can
352 then be processed with the "dot" tool to convert it to postscript or some
353 other suitable format.
354 </p>
355</div>
356
357<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]358<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]359 <a name="dot-postdom">-dot-postdom: Print postdominance tree of function to 'dot' file</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]360</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]361<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]362 <p>
363 This pass, only available in <code>opt</code>, prints the post dominator tree
364 into a <code>.dot</code> graph. This graph can then be processed with the
365 "dot" tool to convert it to postscript or some other suitable format.
366 </p>
367</div>
368
369<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]370<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]371 <a name="dot-postdom-only">-dot-postdom-only: Print postdominance tree of function to 'dot' file (with no function bodies)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]372</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]373<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]374 <p>
375 This pass, only available in <code>opt</code>, prints the post dominator tree
376 into a <code>.dot</code> graph, omitting the function bodies. This graph can
377 then be processed with the "dot" tool to convert it to postscript or some
378 other suitable format.
379 </p>
380</div>
381
382<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]383<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]384 <a name="globalsmodref-aa">-globalsmodref-aa: Simple mod/ref analysis for globals</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]385</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]386<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]387 <p>
388 This simple pass provides alias and mod/ref information for global values
389 that do not have their address taken, and keeps track of whether functions
390 read or write memory (are "pure"). For this simple (but very common) case,
391 we can provide pretty accurate and useful information.
392 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]393</div>
394
395<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]396<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]397 <a name="instcount">-instcount: Counts the various types of Instructions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]398</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]399<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]400 <p>
401 This pass collects the count of all instructions and reports them
402 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]403</div>
404
405<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]406<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]407 <a name="intervals">-intervals: Interval Partition Construction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]408</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]409<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]410 <p>
411 This analysis calculates and represents the interval partition of a function,
412 or a preexisting interval partition.
413 </p>
414
415 <p>
416 In this way, the interval partition may be used to reduce a flow graph down
417 to its degenerate single node interval partition (unless it is irreducible).
418 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]419</div>
420
421<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]422<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]423 <a name="iv-users">-iv-users: Induction Variable Users</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]424</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]425<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]426 <p>Bookkeeping for "interesting" users of expressions computed from
427 induction variables.</p>
428</div>
429
430<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]431<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]432 <a name="lazy-value-info">-lazy-value-info: Lazy Value Information Analysis</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]433</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]434<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]435 <p>Interface for lazy computation of value constraint information.</p>
436</div>
437
438<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]439<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]440 <a name="lda">-lda: Loop Dependence Analysis</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]441</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]442<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]443 <p>Loop dependence analysis framework, which is used to detect dependences in
444 memory accesses in loops.</p>
445</div>
446
447<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]448<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]449 <a name="libcall-aa">-libcall-aa: LibCall Alias Analysis</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]450</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]451<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]452 <p>LibCall Alias Analysis.</p>
453</div>
454
455<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]456<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]457 <a name="lint">-lint: Statically lint-checks LLVM IR</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]458</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]459<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]460 <p>This pass statically checks for common and easily-identified constructs
461 which produce undefined or likely unintended behavior in LLVM IR.</p>
462
463 <p>It is not a guarantee of correctness, in two ways. First, it isn't
464 comprehensive. There are checks which could be done statically which are
465 not yet implemented. Some of these are indicated by TODO comments, but
466 those aren't comprehensive either. Second, many conditions cannot be
467 checked statically. This pass does no dynamic instrumentation, so it
468 can't check for all possible problems.</p>
469
470 <p>Another limitation is that it assumes all code will be executed. A store
471 through a null pointer in a basic block which is never reached is harmless,
472 but this pass will warn about it anyway.</p>
473
474 <p>Optimization passes may make conditions that this pass checks for more or
475 less obvious. If an optimization pass appears to be introducing a warning,
476 it may be that the optimization pass is merely exposing an existing
477 condition in the code.</p>
478
479 <p>This code may be run before instcombine. In many cases, instcombine checks
480 for the same kinds of things and turns instructions with undefined behavior
481 into unreachable (or equivalent). Because of this, this pass makes some
482 effort to look through bitcasts and so on.
483 </p>
484</div>
485
486<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]487<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]488 <a name="loops">-loops: Natural Loop Information</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]489</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]490<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]491 <p>
492 This analysis is used to identify natural loops and determine the loop depth
493 of various nodes of the CFG. Note that the loops identified may actually be
494 several natural loops that share the same header node... not just a single
495 natural loop.
496 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]497</div>
498
499<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]500<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]501 <a name="memdep">-memdep: Memory Dependence Analysis</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]502</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]503<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]504 <p>
505 An analysis that determines, for a given memory operation, what preceding
506 memory operations it depends on. It builds on alias analysis information, and
507 tries to provide a lazy, caching interface to a common kind of alias
508 information query.
509 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]510</div>
511
512<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]513<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]514 <a name="module-debuginfo">-module-debuginfo: Decodes module-level debug info</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]515</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]516<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]517 <p>This pass decodes the debug info metadata in a module and prints in a
518 (sufficiently-prepared-) human-readable form.
519
520 For example, run this pass from opt along with the -analyze option, and
521 it'll print to standard output.
522 </p>
523</div>
524
525<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]526<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]527 <a name="no-aa">-no-aa: No Alias Analysis (always returns 'may' alias)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]528</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]529<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]530 <p>
531 Always returns "I don't know" for alias queries. NoAA is unlike other alias
532 analysis implementations, in that it does not chain to a previous analysis. As
533 such it doesn't follow many of the rules that other alias analyses must.
534 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]535</div>
536
537<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]538<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]539 <a name="no-profile">-no-profile: No Profile Information</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]540</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]541<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]542 <p>
543 The default "no profile" implementation of the abstract
544 <code>ProfileInfo</code> interface.
545 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]546</div>
547
548<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]549<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]550 <a name="postdomfrontier">-postdomfrontier: Post-Dominance Frontier Construction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]551</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]552<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]553 <p>
554 This pass is a simple post-dominator construction algorithm for finding
555 post-dominator frontiers.
556 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]557</div>
558
559<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]560<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]561 <a name="postdomtree">-postdomtree: Post-Dominator Tree Construction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]562</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]563<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]564 <p>
565 This pass is a simple post-dominator construction algorithm for finding
566 post-dominators.
567 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]568</div>
569
570<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]571<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]572 <a name="print-alias-sets">-print-alias-sets: Alias Set Printer</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]573</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]574<div>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]575 <p>Yet to be written.</p>
576</div>
577
578<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]579<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]580 <a name="print-callgraph">-print-callgraph: Print a call graph</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]581</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]582<div>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]583 <p>
584 This pass, only available in <code>opt</code>, prints the call graph to
Dan Gohman52fdaed2010-08-20 01:03:44 +0000[diff] [blame]585 standard error in a human-readable form.
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]586 </p>
587</div>
588
589<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]590<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]591 <a name="print-callgraph-sccs">-print-callgraph-sccs: Print SCCs of the Call Graph</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]592</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]593<div>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]594 <p>
595 This pass, only available in <code>opt</code>, prints the SCCs of the call
Dan Gohman52fdaed2010-08-20 01:03:44 +0000[diff] [blame]596 graph to standard error in a human-readable form.
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]597 </p>
598</div>
599
600<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]601<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]602 <a name="print-cfg-sccs">-print-cfg-sccs: Print SCCs of each function CFG</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]603</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]604<div>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]605 <p>
606 This pass, only available in <code>opt</code>, prints the SCCs of each
Dan Gohman52fdaed2010-08-20 01:03:44 +0000[diff] [blame]607 function CFG to standard error in a human-readable form.
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]608 </p>
609</div>
610
611<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]612<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]613 <a name="print-dbginfo">-print-dbginfo: Print debug info in human readable form</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]614</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]615<div>
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]616 <p>Pass that prints instructions, and associated debug info:</p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]617 <ul>
618
619 <li>source/line/col information</li>
620 <li>original variable name</li>
621 <li>original type name</li>
622 </ul>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]623</div>
624
625<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]626<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]627 <a name="print-dom-info">-print-dom-info: Dominator Info Printer</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]628</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]629<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]630 <p>Dominator Info Printer.</p>
631</div>
632
633<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]634<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]635 <a name="print-externalfnconstants">-print-externalfnconstants: Print external fn callsites passed constants</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]636</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]637<div>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]638 <p>
639 This pass, only available in <code>opt</code>, prints out call sites to
640 external functions that are called with constant arguments. This can be
641 useful when looking for standard library functions we should constant fold
642 or handle in alias analyses.
643 </p>
644</div>
645
646<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]647<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]648 <a name="print-function">-print-function: Print function to stderr</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]649</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]650<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]651 <p>
652 The <code>PrintFunctionPass</code> class is designed to be pipelined with
653 other <code>FunctionPass</code>es, and prints out the functions of the module
654 as they are processed.
655 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]656</div>
657
658<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]659<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]660 <a name="print-module">-print-module: Print module to stderr</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]661</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]662<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]663 <p>
664 This pass simply prints out the entire module when it is executed.
665 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]666</div>
667
668<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]669<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]670 <a name="print-used-types">-print-used-types: Find Used Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]671</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]672<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]673 <p>
674 This pass is used to seek out all of the types in use by the program. Note
675 that this analysis explicitly does not include types only used by the symbol
676 table.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]677</div>
678
679<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]680<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]681 <a name="profile-estimator">-profile-estimator: Estimate profiling information</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]682</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]683<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]684 <p>Profiling information that estimates the profiling information
685 in a very crude and unimaginative way.
686 </p>
687</div>
688
689<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]690<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]691 <a name="profile-loader">-profile-loader: Load profile information from llvmprof.out</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]692</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]693<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]694 <p>
695 A concrete implementation of profiling information that loads the information
696 from a profile dump file.
697 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]698</div>
699
700<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]701<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]702 <a name="profile-verifier">-profile-verifier: Verify profiling information</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]703</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]704<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]705 <p>Pass that checks profiling information for plausibility.</p>
706</div>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]707<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]708 <a name="regions">-regions: Detect single entry single exit regions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]709</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]710<div>
Tobias Grosserf96b0062010-07-22 07:46:31 +0000[diff] [blame]711 <p>
712 The <code>RegionInfo</code> pass detects single entry single exit regions in a
713 function, where a region is defined as any subgraph that is connected to the
714 remaining graph at only two spots. Furthermore, an hierarchical region tree is
715 built.
716 </p>
717</div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]718
719<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]720<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]721 <a name="scalar-evolution">-scalar-evolution: Scalar Evolution Analysis</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]722</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]723<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]724 <p>
725 The <code>ScalarEvolution</code> analysis can be used to analyze and
726 catagorize scalar expressions in loops. It specializes in recognizing general
727 induction variables, representing them with the abstract and opaque
728 <code>SCEV</code> class. Given this analysis, trip counts of loops and other
729 important properties can be obtained.
730 </p>
731
732 <p>
733 This analysis is primarily useful for induction variable substitution and
734 strength reduction.
735 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]736</div>
737
738<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]739<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]740 <a name="scev-aa">-scev-aa: ScalarEvolution-based Alias Analysis</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]741</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]742<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]743 <p>Simple alias analysis implemented in terms of ScalarEvolution queries.
744
745 This differs from traditional loop dependence analysis in that it tests
746 for dependencies within a single iteration of a loop, rather than
747 dependencies between different iterations.
748
749 ScalarEvolution has a more complete understanding of pointer arithmetic
750 than BasicAliasAnalysis' collection of ad-hoc analyses.
751 </p>
752</div>
753
754<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]755<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]756 <a name="targetdata">-targetdata: Target Data Layout</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]757</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]758<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]759 <p>Provides other passes access to information on how the size and alignment
760 required by the the target ABI for various data types.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]761</div>
762
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]763</div>
764
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]765<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]766<h2><a name="transforms">Transform Passes</a></h2>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]767<div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]768 <p>This section describes the LLVM Transform Passes.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]769
770<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]771<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]772 <a name="adce">-adce: Aggressive Dead Code Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]773</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]774<div>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]775 <p>ADCE aggressively tries to eliminate code. This pass is similar to
776 <a href="#dce">DCE</a> but it assumes that values are dead until proven
777 otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
778 the liveness of values.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]779</div>
780
781<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]782<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]783 <a name="always-inline">-always-inline: Inliner for always_inline functions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]784</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]785<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]786 <p>A custom inliner that handles only functions that are marked as
787 "always inline".</p>
788</div>
789
790<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]791<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]792 <a name="argpromotion">-argpromotion: Promote 'by reference' arguments to scalars</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]793</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]794<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]795 <p>
796 This pass promotes "by reference" arguments to be "by value" arguments. In
797 practice, this means looking for internal functions that have pointer
798 arguments. If it can prove, through the use of alias analysis, that an
799 argument is *only* loaded, then it can pass the value into the function
800 instead of the address of the value. This can cause recursive simplification
801 of code and lead to the elimination of allocas (especially in C++ template
802 code like the STL).
803 </p>
804
805 <p>
806 This pass also handles aggregate arguments that are passed into a function,
807 scalarizing them if the elements of the aggregate are only loaded. Note that
808 it refuses to scalarize aggregates which would require passing in more than
809 three operands to the function, because passing thousands of operands for a
810 large array or structure is unprofitable!
811 </p>
812
813 <p>
814 Note that this transformation could also be done for arguments that are only
815 stored to (returning the value instead), but does not currently. This case
816 would be best handled when and if LLVM starts supporting multiple return
817 values from functions.
818 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]819</div>
820
821<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]822<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]823 <a name="block-placement">-block-placement: Profile Guided Basic Block Placement</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]824</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]825<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]826 <p>This pass is a very simple profile guided basic block placement algorithm.
827 The idea is to put frequently executed blocks together at the start of the
828 function and hopefully increase the number of fall-through conditional
829 branches. If there is no profile information for a particular function, this
830 pass basically orders blocks in depth-first order.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]831</div>
832
833<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]834<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]835 <a name="break-crit-edges">-break-crit-edges: Break critical edges in CFG</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]836</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]837<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]838 <p>
839 Break all of the critical edges in the CFG by inserting a dummy basic block.
840 It may be "required" by passes that cannot deal with critical edges. This
841 transformation obviously invalidates the CFG, but can update forward dominator
842 (set, immediate dominators, tree, and frontier) information.
843 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]844</div>
845
846<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]847<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]848 <a name="codegenprepare">-codegenprepare: Optimize for code generation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]849</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]850<div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]851 This pass munges the code in the input function to better prepare it for
852 SelectionDAG-based code generation. This works around limitations in it's
853 basic-block-at-a-time approach. It should eventually be removed.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]854</div>
855
856<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]857<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]858 <a name="constmerge">-constmerge: Merge Duplicate Global Constants</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]859</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]860<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]861 <p>
862 Merges duplicate global constants together into a single constant that is
863 shared. This is useful because some passes (ie TraceValues) insert a lot of
864 string constants into the program, regardless of whether or not an existing
865 string is available.
866 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]867</div>
868
869<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]870<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]871 <a name="constprop">-constprop: Simple constant propagation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]872</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]873<div>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]874 <p>This file implements constant propagation and merging. It looks for
875 instructions involving only constant operands and replaces them with a
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]876 constant value instead of an instruction. For example:</p>
877 <blockquote><pre>add i32 1, 2</pre></blockquote>
878 <p>becomes</p>
879 <blockquote><pre>i32 3</pre></blockquote>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]880 <p>NOTE: this pass has a habit of making definitions be dead. It is a good
881 idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
882 sometime after running this pass.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]883</div>
884
885<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]886<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]887 <a name="dce">-dce: Dead Code Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]888</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]889<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]890 <p>
891 Dead code elimination is similar to <a href="#die">dead instruction
892 elimination</a>, but it rechecks instructions that were used by removed
893 instructions to see if they are newly dead.
894 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]895</div>
896
897<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]898<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]899 <a name="deadargelim">-deadargelim: Dead Argument Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]900</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]901<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]902 <p>
903 This pass deletes dead arguments from internal functions. Dead argument
904 elimination removes arguments which are directly dead, as well as arguments
905 only passed into function calls as dead arguments of other functions. This
906 pass also deletes dead arguments in a similar way.
907 </p>
908
909 <p>
910 This pass is often useful as a cleanup pass to run after aggressive
911 interprocedural passes, which add possibly-dead arguments.
912 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]913</div>
914
915<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]916<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]917 <a name="deadtypeelim">-deadtypeelim: Dead Type Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]918</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]919<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]920 <p>
921 This pass is used to cleanup the output of GCC. It eliminate names for types
922 that are unused in the entire translation unit, using the <a
923 href="#findusedtypes">find used types</a> pass.
924 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]925</div>
926
927<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]928<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]929 <a name="die">-die: Dead Instruction Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]930</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]931<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]932 <p>
933 Dead instruction elimination performs a single pass over the function,
934 removing instructions that are obviously dead.
935 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]936</div>
937
938<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]939<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]940 <a name="dse">-dse: Dead Store Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]941</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]942<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]943 <p>
944 A trivial dead store elimination that only considers basic-block local
945 redundant stores.
946 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]947</div>
948
949<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]950<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]951 <a name="functionattrs">-functionattrs: Deduce function attributes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]952</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]953<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]954 <p>A simple interprocedural pass which walks the call-graph, looking for
955 functions which do not access or only read non-local memory, and marking them
956 readnone/readonly. In addition, it marks function arguments (of pointer type)
957 'nocapture' if a call to the function does not create any copies of the pointer
958 value that outlive the call. This more or less means that the pointer is only
959 dereferenced, and not returned from the function or stored in a global.
960 This pass is implemented as a bottom-up traversal of the call-graph.
961 </p>
962</div>
963
964<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]965<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]966 <a name="globaldce">-globaldce: Dead Global Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]967</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]968<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]969 <p>
970 This transform is designed to eliminate unreachable internal globals from the
971 program. It uses an aggressive algorithm, searching out globals that are
972 known to be alive. After it finds all of the globals which are needed, it
973 deletes whatever is left over. This allows it to delete recursive chunks of
974 the program which are unreachable.
975 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]976</div>
977
978<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]979<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]980 <a name="globalopt">-globalopt: Global Variable Optimizer</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]981</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]982<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]983 <p>
984 This pass transforms simple global variables that never have their address
985 taken. If obviously true, it marks read/write globals as constant, deletes
986 variables only stored to, etc.
987 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]988</div>
989
990<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]991<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]992 <a name="gvn">-gvn: Global Value Numbering</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]993</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]994<div>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]995 <p>
Chris Lattner60f03402009-10-10 18:40:48 +0000[diff] [blame]996 This pass performs global value numbering to eliminate fully and partially
997 redundant instructions. It also performs redundant load elimination.
Matthijs Kooijman845f5242008-06-05 07:55:49 +0000[diff] [blame]998 </p>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]999</div>
1000
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1001<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1002<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1003 <a name="indvars">-indvars: Canonicalize Induction Variables</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1004</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1005<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1006 <p>
1007 This transformation analyzes and transforms the induction variables (and
1008 computations derived from them) into simpler forms suitable for subsequent
1009 analysis and transformation.
1010 </p>
1011
1012 <p>
1013 This transformation makes the following changes to each loop with an
1014 identifiable induction variable:
1015 </p>
1016
1017 <ol>
1018 <li>All loops are transformed to have a <em>single</em> canonical
1019 induction variable which starts at zero and steps by one.</li>
1020 <li>The canonical induction variable is guaranteed to be the first PHI node
1021 in the loop header block.</li>
1022 <li>Any pointer arithmetic recurrences are raised to use array
1023 subscripts.</li>
1024 </ol>
1025
1026 <p>
1027 If the trip count of a loop is computable, this pass also makes the following
1028 changes:
1029 </p>
1030
1031 <ol>
1032 <li>The exit condition for the loop is canonicalized to compare the
1033 induction value against the exit value. This turns loops like:
1034 <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
1035 into
1036 <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
1037 <li>Any use outside of the loop of an expression derived from the indvar
1038 is changed to compute the derived value outside of the loop, eliminating
1039 the dependence on the exit value of the induction variable. If the only
1040 purpose of the loop is to compute the exit value of some derived
1041 expression, this transformation will make the loop dead.</li>
Gordon Henriksene626bbe2007-11-04 16:17:00 +0000[diff] [blame]1042 </ol>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1043
1044 <p>
1045 This transformation should be followed by strength reduction after all of the
1046 desired loop transformations have been performed. Additionally, on targets
1047 where it is profitable, the loop could be transformed to count down to zero
1048 (the "do loop" optimization).
1049 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1050</div>
1051
1052<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1053<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1054 <a name="inline">-inline: Function Integration/Inlining</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1055</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1056<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1057 <p>
1058 Bottom-up inlining of functions into callees.
1059 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1060</div>
1061
1062<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1063<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1064 <a name="insert-edge-profiling">-insert-edge-profiling: Insert instrumentation for edge profiling</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1065</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1066<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1067 <p>
1068 This pass instruments the specified program with counters for edge profiling.
1069 Edge profiling can give a reasonable approximation of the hot paths through a
1070 program, and is used for a wide variety of program transformations.
1071 </p>
1072
1073 <p>
1074 Note that this implementation is very naïve. It inserts a counter for
1075 <em>every</em> edge in the program, instead of using control flow information
1076 to prune the number of counters inserted.
1077 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1078</div>
1079
1080<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1081<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1082 <a name="insert-optimal-edge-profiling">-insert-optimal-edge-profiling: Insert optimal instrumentation for edge profiling</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1083</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1084<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1085 <p>This pass instruments the specified program with counters for edge profiling.
1086 Edge profiling can give a reasonable approximation of the hot paths through a
1087 program, and is used for a wide variety of program transformations.
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1088 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1089</div>
1090
1091<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1092<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1093 <a name="instcombine">-instcombine: Combine redundant instructions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1094</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1095<div>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1096 <p>
1097 Combine instructions to form fewer, simple
1098 instructions. This pass does not modify the CFG This pass is where algebraic
1099 simplification happens.
1100 </p>
1101
1102 <p>
1103 This pass combines things like:
1104 </p>
1105
1106<blockquote><pre
1107>%Y = add i32 %X, 1
1108%Z = add i32 %Y, 1</pre></blockquote>
1109
1110 <p>
1111 into:
1112 </p>
1113
1114<blockquote><pre
1115>%Z = add i32 %X, 2</pre></blockquote>
1116
1117 <p>
1118 This is a simple worklist driven algorithm.
1119 </p>
1120
1121 <p>
1122 This pass guarantees that the following canonicalizations are performed on
1123 the program:
1124 </p>
1125
1126 <ul>
1127 <li>If a binary operator has a constant operand, it is moved to the right-
1128 hand side.</li>
1129 <li>Bitwise operators with constant operands are always grouped so that
1130 shifts are performed first, then <code>or</code>s, then
1131 <code>and</code>s, then <code>xor</code>s.</li>
1132 <li>Compare instructions are converted from <code>&lt;</code>,
1133 <code>&gt;</code>, <code>≤</code>, or <code>≥</code> to
1134 <code>=</code> or <code>≠</code> if possible.</li>
1135 <li>All <code>cmp</code> instructions on boolean values are replaced with
1136 logical operations.</li>
1137 <li><code>add <var>X</var>, <var>X</var></code> is represented as
1138 <code>mul <var>X</var>, 2</code> ⇒ <code>shl <var>X</var>, 1</code></li>
1139 <li>Multiplies with a constant power-of-two argument are transformed into
1140 shifts.</li>
1141 <li>… etc.</li>
1142 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1143</div>
1144
1145<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1146<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1147 <a name="internalize">-internalize: Internalize Global Symbols</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1148</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1149<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1150 <p>
1151 This pass loops over all of the functions in the input module, looking for a
1152 main function. If a main function is found, all other functions and all
1153 global variables with initializers are marked as internal.
1154 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1155</div>
1156
1157<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1158<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1159 <a name="ipconstprop">-ipconstprop: Interprocedural constant propagation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1160</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1161<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1162 <p>
1163 This pass implements an <em>extremely</em> simple interprocedural constant
1164 propagation pass. It could certainly be improved in many different ways,
1165 like using a worklist. This pass makes arguments dead, but does not remove
1166 them. The existing dead argument elimination pass should be run after this
1167 to clean up the mess.
1168 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1169</div>
1170
1171<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1172<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1173 <a name="ipsccp">-ipsccp: Interprocedural Sparse Conditional Constant Propagation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1174</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1175<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1176 <p>
1177 An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
1178 Propagation</a>.
1179 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1180</div>
1181
1182<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1183<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]1184 <a name="jump-threading">-jump-threading: Jump Threading</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1185</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1186<div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1187 <p>
1188 Jump threading tries to find distinct threads of control flow running through
1189 a basic block. This pass looks at blocks that have multiple predecessors and
1190 multiple successors. If one or more of the predecessors of the block can be
1191 proven to always cause a jump to one of the successors, we forward the edge
1192 from the predecessor to the successor by duplicating the contents of this
1193 block.
1194 </p>
1195 <p>
1196 An example of when this can occur is code like this:
1197 </p>
1198
1199 <pre
1200>if () { ...
1201 X = 4;
1202}
1203if (X &lt; 3) {</pre>
1204
1205 <p>
1206 In this case, the unconditional branch at the end of the first if can be
1207 revectored to the false side of the second if.
1208 </p>
1209</div>
1210
1211<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1212<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1213 <a name="lcssa">-lcssa: Loop-Closed SSA Form Pass</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1214</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1215<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1216 <p>
1217 This pass transforms loops by placing phi nodes at the end of the loops for
1218 all values that are live across the loop boundary. For example, it turns
1219 the left into the right code:
1220 </p>
1221
1222 <pre
1223>for (...) for (...)
1224 if (c) if (c)
1225 X1 = ... X1 = ...
1226 else else
1227 X2 = ... X2 = ...
1228 X3 = phi(X1, X2) X3 = phi(X1, X2)
1229... = X3 + 4 X4 = phi(X3)
1230 ... = X4 + 4</pre>
1231
1232 <p>
1233 This is still valid LLVM; the extra phi nodes are purely redundant, and will
1234 be trivially eliminated by <code>InstCombine</code>. The major benefit of
1235 this transformation is that it makes many other loop optimizations, such as
1236 LoopUnswitching, simpler.
1237 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1238</div>
1239
1240<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1241<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1242 <a name="licm">-licm: Loop Invariant Code Motion</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1243</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1244<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1245 <p>
1246 This pass performs loop invariant code motion, attempting to remove as much
1247 code from the body of a loop as possible. It does this by either hoisting
1248 code into the preheader block, or by sinking code to the exit blocks if it is
1249 safe. This pass also promotes must-aliased memory locations in the loop to
1250 live in registers, thus hoisting and sinking "invariant" loads and stores.
1251 </p>
1252
1253 <p>
1254 This pass uses alias analysis for two purposes:
1255 </p>
1256
1257 <ul>
1258 <li>Moving loop invariant loads and calls out of loops. If we can determine
1259 that a load or call inside of a loop never aliases anything stored to,
1260 we can hoist it or sink it like any other instruction.</li>
1261 <li>Scalar Promotion of Memory - If there is a store instruction inside of
1262 the loop, we try to move the store to happen AFTER the loop instead of
1263 inside of the loop. This can only happen if a few conditions are true:
1264 <ul>
1265 <li>The pointer stored through is loop invariant.</li>
1266 <li>There are no stores or loads in the loop which <em>may</em> alias
1267 the pointer. There are no calls in the loop which mod/ref the
1268 pointer.</li>
1269 </ul>
1270 If these conditions are true, we can promote the loads and stores in the
1271 loop of the pointer to use a temporary alloca'd variable. We then use
1272 the mem2reg functionality to construct the appropriate SSA form for the
1273 variable.</li>
1274 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1275</div>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1276
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1277<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1278<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]1279 <a name="loop-deletion">-loop-deletion: Delete dead loops</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1280</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1281<div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1282 <p>
1283 This file implements the Dead Loop Deletion Pass. This pass is responsible
1284 for eliminating loops with non-infinite computable trip counts that have no
1285 side effects or volatile instructions, and do not contribute to the
1286 computation of the function's return value.
1287 </p>
1288</div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1289
1290<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1291<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1292 <a name="loop-extract">-loop-extract: Extract loops into new functions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1293</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1294<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1295 <p>
1296 A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
1297 extract each top-level loop into its own new function. If the loop is the
1298 <em>only</em> loop in a given function, it is not touched. This is a pass most
1299 useful for debugging via bugpoint.
1300 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1301</div>
1302
1303<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1304<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1305 <a name="loop-extract-single">-loop-extract-single: Extract at most one loop into a new function</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1306</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1307<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1308 <p>
1309 Similar to <a href="#loop-extract">Extract loops into new functions</a>,
1310 this pass extracts one natural loop from the program into a function if it
1311 can. This is used by bugpoint.
1312 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1313</div>
1314
1315<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1316<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1317 <a name="loop-reduce">-loop-reduce: Loop Strength Reduction</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1318</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1319<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1320 <p>
1321 This pass performs a strength reduction on array references inside loops that
1322 have as one or more of their components the loop induction variable. This is
1323 accomplished by creating a new value to hold the initial value of the array
1324 access for the first iteration, and then creating a new GEP instruction in
1325 the loop to increment the value by the appropriate amount.
1326 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1327</div>
1328
1329<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1330<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1331 <a name="loop-rotate">-loop-rotate: Rotate Loops</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1332</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1333<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1334 <p>A simple loop rotation transformation.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1335</div>
1336
1337<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1338<h3>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1339 <a name="loop-simplify">-loop-simplify: Canonicalize natural loops</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1340</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1341<div>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1342 <p>
1343 This pass performs several transformations to transform natural loops into a
1344 simpler form, which makes subsequent analyses and transformations simpler and
1345 more effective.
1346 </p>
1347
1348 <p>
1349 Loop pre-header insertion guarantees that there is a single, non-critical
1350 entry edge from outside of the loop to the loop header. This simplifies a
1351 number of analyses and transformations, such as LICM.
1352 </p>
1353
1354 <p>
1355 Loop exit-block insertion guarantees that all exit blocks from the loop
1356 (blocks which are outside of the loop that have predecessors inside of the
1357 loop) only have predecessors from inside of the loop (and are thus dominated
1358 by the loop header). This simplifies transformations such as store-sinking
1359 that are built into LICM.
1360 </p>
1361
1362 <p>
1363 This pass also guarantees that loops will have exactly one backedge.
1364 </p>
1365
1366 <p>
1367 Note that the simplifycfg pass will clean up blocks which are split out but
1368 end up being unnecessary, so usage of this pass should not pessimize
1369 generated code.
1370 </p>
1371
1372 <p>
1373 This pass obviously modifies the CFG, but updates loop information and
1374 dominator information.
1375 </p>
1376</div>
1377
1378<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1379<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1380 <a name="loop-unroll">-loop-unroll: Unroll loops</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1381</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1382<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1383 <p>
1384 This pass implements a simple loop unroller. It works best when loops have
1385 been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
1386 allowing it to determine the trip counts of loops easily.
1387 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1388</div>
1389
1390<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1391<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1392 <a name="loop-unswitch">-loop-unswitch: Unswitch loops</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1393</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1394<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1395 <p>
1396 This pass transforms loops that contain branches on loop-invariant conditions
1397 to have multiple loops. For example, it turns the left into the right code:
1398 </p>
1399
1400 <pre
1401>for (...) if (lic)
1402 A for (...)
1403 if (lic) A; B; C
1404 B else
1405 C for (...)
1406 A; C</pre>
1407
1408 <p>
1409 This can increase the size of the code exponentially (doubling it every time
1410 a loop is unswitched) so we only unswitch if the resultant code will be
1411 smaller than a threshold.
1412 </p>
1413
1414 <p>
1415 This pass expects LICM to be run before it to hoist invariant conditions out
1416 of the loop, to make the unswitching opportunity obvious.
1417 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1418</div>
1419
1420<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1421<h3>
Eli Friedmande8ec5b2011-03-19 04:55:29 +0000[diff] [blame]1422 <a name="loweratomic">-loweratomic: Lower atomic intrinsics to non-atomic form</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1423</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1424<div>
Peter Collingbourne3bababf2010-08-03 16:19:16 +0000[diff] [blame]1425 <p>
1426 This pass lowers atomic intrinsics to non-atomic form for use in a known
1427 non-preemptible environment.
1428 </p>
1429
1430 <p>
1431 The pass does not verify that the environment is non-preemptible (in
1432 general this would require knowledge of the entire call graph of the
1433 program including any libraries which may not be available in bitcode form);
1434 it simply lowers every atomic intrinsic.
1435 </p>
1436</div>
1437
1438<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1439<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1440 <a name="lowerinvoke">-lowerinvoke: Lower invoke and unwind, for unwindless code generators</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1441</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1442<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1443 <p>
1444 This transformation is designed for use by code generators which do not yet
1445 support stack unwinding. This pass supports two models of exception handling
1446 lowering, the 'cheap' support and the 'expensive' support.
1447 </p>
1448
1449 <p>
1450 'Cheap' exception handling support gives the program the ability to execute
1451 any program which does not "throw an exception", by turning 'invoke'
1452 instructions into calls and by turning 'unwind' instructions into calls to
1453 abort(). If the program does dynamically use the unwind instruction, the
1454 program will print a message then abort.
1455 </p>
1456
1457 <p>
1458 'Expensive' exception handling support gives the full exception handling
1459 support to the program at the cost of making the 'invoke' instruction
1460 really expensive. It basically inserts setjmp/longjmp calls to emulate the
1461 exception handling as necessary.
1462 </p>
1463
1464 <p>
1465 Because the 'expensive' support slows down programs a lot, and EH is only
1466 used for a subset of the programs, it must be specifically enabled by the
1467 <tt>-enable-correct-eh-support</tt> option.
1468 </p>
1469
1470 <p>
1471 Note that after this pass runs the CFG is not entirely accurate (exceptional
1472 control flow edges are not correct anymore) so only very simple things should
1473 be done after the lowerinvoke pass has run (like generation of native code).
1474 This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
1475 support the invoke instruction yet" lowering pass.
1476 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1477</div>
1478
1479<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1480<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1481 <a name="lowersetjmp">-lowersetjmp: Lower Set Jump</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1482</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1483<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1484 <p>
1485 Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
1486 instructions as necessary.
1487 </p>
1488
1489 <p>
1490 Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
1491 call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
1492 This unwinds the stack for us calling all of the destructors for
1493 objects allocated on the stack.
1494 </p>
1495
1496 <p>
1497 At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
1498 removed. The calls in a function that have a <tt>setjmp</tt> are converted to
1499 invoke where the except part checks to see if it's a <tt>longjmp</tt>
1500 exception and, if so, if it's handled in the function. If it is, then it gets
1501 the value returned by the <tt>longjmp</tt> and goes to where the basic block
1502 was split. <tt>invoke</tt> instructions are handled in a similar fashion with
1503 the original except block being executed if it isn't a <tt>longjmp</tt>
1504 except that is handled by that function.
1505 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1506</div>
1507
1508<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1509<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1510 <a name="lowerswitch">-lowerswitch: Lower SwitchInst's to branches</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1511</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1512<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1513 <p>
1514 Rewrites <tt>switch</tt> instructions with a sequence of branches, which
1515 allows targets to get away with not implementing the switch instruction until
1516 it is convenient.
1517 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1518</div>
1519
1520<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1521<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1522 <a name="mem2reg">-mem2reg: Promote Memory to Register</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1523</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1524<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1525 <p>
1526 This file promotes memory references to be register references. It promotes
1527 <tt>alloca</tt> instructions which only have <tt>load</tt>s and
1528 <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
1529 frontiers to place <tt>phi</tt> nodes, then traversing the function in
1530 depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
1531 appropriate. This is just the standard SSA construction algorithm to construct
1532 "pruned" SSA form.
1533 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1534</div>
1535
1536<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1537<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]1538 <a name="memcpyopt">-memcpyopt: MemCpy Optimization</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1539</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1540<div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1541 <p>
1542 This pass performs various transformations related to eliminating memcpy
1543 calls, or transforming sets of stores into memset's.
1544 </p>
1545</div>
1546
1547<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1548<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1549 <a name="mergefunc">-mergefunc: Merge Functions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1550</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1551<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1552 <p>This pass looks for equivalent functions that are mergable and folds them.
1553
1554 A hash is computed from the function, based on its type and number of
1555 basic blocks.
1556
1557 Once all hashes are computed, we perform an expensive equality comparison
1558 on each function pair. This takes n^2/2 comparisons per bucket, so it's
1559 important that the hash function be high quality. The equality comparison
1560 iterates through each instruction in each basic block.
1561
1562 When a match is found the functions are folded. If both functions are
1563 overridable, we move the functionality into a new internal function and
1564 leave two overridable thunks to it.
1565 </p>
1566</div>
1567
1568<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1569<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1570 <a name="mergereturn">-mergereturn: Unify function exit nodes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1571</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1572<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1573 <p>
1574 Ensure that functions have at most one <tt>ret</tt> instruction in them.
1575 Additionally, it keeps track of which node is the new exit node of the CFG.
1576 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1577</div>
1578
1579<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1580<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1581 <a name="partial-inliner">-partial-inliner: Partial Inliner</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1582</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1583<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1584 <p>This pass performs partial inlining, typically by inlining an if
1585 statement that surrounds the body of the function.
1586 </p>
1587</div>
1588
1589<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1590<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1591 <a name="prune-eh">-prune-eh: Remove unused exception handling info</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1592</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1593<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1594 <p>
1595 This file implements a simple interprocedural pass which walks the call-graph,
1596 turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
1597 only if the callee cannot throw an exception. It implements this as a
1598 bottom-up traversal of the call-graph.
1599 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1600</div>
1601
1602<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1603<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1604 <a name="reassociate">-reassociate: Reassociate expressions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1605</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1606<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1607 <p>
1608 This pass reassociates commutative expressions in an order that is designed
1609 to promote better constant propagation, GCSE, LICM, PRE, etc.
1610 </p>
1611
1612 <p>
1613 For example: 4 + (<var>x</var> + 5) ⇒ <var>x</var> + (4 + 5)
1614 </p>
1615
1616 <p>
1617 In the implementation of this algorithm, constants are assigned rank = 0,
1618 function arguments are rank = 1, and other values are assigned ranks
1619 corresponding to the reverse post order traversal of current function
1620 (starting at 2), which effectively gives values in deep loops higher rank
1621 than values not in loops.
1622 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1623</div>
1624
1625<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1626<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1627 <a name="reg2mem">-reg2mem: Demote all values to stack slots</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1628</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1629<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1630 <p>
1631 This file demotes all registers to memory references. It is intented to be
1632 the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]1633 <tt>load</tt> instructions, the only values live across basic blocks are
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1634 <tt>alloca</tt> instructions and <tt>load</tt> instructions before
1635 <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
1636 easier. To make later hacking easier, the entry block is split into two, such
1637 that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
1638 entry block.
1639 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1640</div>
1641
1642<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1643<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]1644 <a name="scalarrepl">-scalarrepl: Scalar Replacement of Aggregates (DT)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1645</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1646<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1647 <p>
1648 The well-known scalar replacement of aggregates transformation. This
1649 transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
1650 or array) into individual <tt>alloca</tt> instructions for each member if
1651 possible. Then, if possible, it transforms the individual <tt>alloca</tt>
1652 instructions into nice clean scalar SSA form.
1653 </p>
1654
1655 <p>
1656 This combines a simple scalar replacement of aggregates algorithm with the <a
1657 href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
1658 especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
1659 then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
1660 promote works well.
1661 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1662</div>
1663
1664<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1665<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1666 <a name="sccp">-sccp: Sparse Conditional Constant Propagation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1667</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1668<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1669 <p>
1670 Sparse conditional constant propagation and merging, which can be summarized
1671 as:
1672 </p>
1673
1674 <ol>
1675 <li>Assumes values are constant unless proven otherwise</li>
1676 <li>Assumes BasicBlocks are dead unless proven otherwise</li>
1677 <li>Proves values to be constant, and replaces them with constants</li>
1678 <li>Proves conditional branches to be unconditional</li>
1679 </ol>
1680
1681 <p>
1682 Note that this pass has a habit of making definitions be dead. It is a good
1683 idea to to run a DCE pass sometime after running this pass.
1684 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1685</div>
1686
1687<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1688<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1689 <a name="simplify-libcalls">-simplify-libcalls: Simplify well-known library calls</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1690</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1691<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1692 <p>
1693 Applies a variety of small optimizations for calls to specific well-known
1694 function calls (e.g. runtime library functions). For example, a call
1695 <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
1696 transformed into simply <tt>return 3</tt>.
1697 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1698</div>
1699
1700<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1701<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1702 <a name="simplifycfg">-simplifycfg: Simplify the CFG</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1703</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1704<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1705 <p>
1706 Performs dead code elimination and basic block merging. Specifically:
1707 </p>
1708
1709 <ol>
1710 <li>Removes basic blocks with no predecessors.</li>
1711 <li>Merges a basic block into its predecessor if there is only one and the
1712 predecessor only has one successor.</li>
1713 <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
1714 <li>Eliminates a basic block that only contains an unconditional
1715 branch.</li>
1716 </ol>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1717</div>
1718
1719<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1720<h3>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1721 <a name="sink">-sink: Code sinking</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1722</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1723<div>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1724 <p>This pass moves instructions into successor blocks, when possible, so that
1725 they aren't executed on paths where their results aren't needed.
1726 </p>
1727</div>
1728
1729<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1730<h3>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1731 <a name="sretpromotion">-sretpromotion: Promote sret arguments to multiple ret values</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1732</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1733<div>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1734 <p>
1735 This pass finds functions that return a struct (using a pointer to the struct
1736 as the first argument of the function, marked with the '<tt>sret</tt>' attribute) and
1737 replaces them with a new function that simply returns each of the elements of
1738 that struct (using multiple return values).
1739 </p>
1740
1741 <p>
1742 This pass works under a number of conditions:
1743 </p>
1744
1745 <ul>
1746 <li>The returned struct must not contain other structs</li>
1747 <li>The returned struct must only be used to load values from</li>
1748 <li>The placeholder struct passed in is the result of an <tt>alloca</tt></li>
1749 </ul>
1750</div>
1751
1752<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1753<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1754 <a name="strip">-strip: Strip all symbols from a module</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1755</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1756<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1757 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1758 performs code stripping. this transformation can delete:
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1759 </p>
1760
1761 <ol>
1762 <li>names for virtual registers</li>
1763 <li>symbols for internal globals and functions</li>
1764 <li>debug information</li>
1765 </ol>
1766
1767 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1768 note that this transformation makes code much less readable, so it should
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1769 only be used in situations where the <tt>strip</tt> utility would be used,
1770 such as reducing code size or making it harder to reverse engineer code.
1771 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1772</div>
1773
1774<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1775<h3>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1776 <a name="strip-dead-debug-info">-strip-dead-debug-info: Strip debug info for unused symbols</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1777</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1778<div>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]1779 <p>
1780 performs code stripping. this transformation can delete:
1781 </p>
1782
1783 <ol>
1784 <li>names for virtual registers</li>
1785 <li>symbols for internal globals and functions</li>
1786 <li>debug information</li>
1787 </ol>
1788
1789 <p>
1790 note that this transformation makes code much less readable, so it should
1791 only be used in situations where the <tt>strip</tt> utility would be used,
1792 such as reducing code size or making it harder to reverse engineer code.
1793 </p>
1794</div>
1795
1796<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1797<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]1798 <a name="strip-dead-prototypes">-strip-dead-prototypes: Strip Unused Function Prototypes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1799</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1800<div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1801 <p>
1802 This pass loops over all of the functions in the input module, looking for
1803 dead declarations and removes them. Dead declarations are declarations of
1804 functions for which no implementation is available (i.e., declarations for
1805 unused library functions).
1806 </p>
1807</div>
1808
1809<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1810<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1811 <a name="strip-debug-declare">-strip-debug-declare: Strip all llvm.dbg.declare intrinsics</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1812</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1813<div>
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1814 <p>This pass implements code stripping. Specifically, it can delete:</p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1815 <ul>
1816 <li>names for virtual registers</li>
1817 <li>symbols for internal globals and functions</li>
1818 <li>debug information</li>
1819 </ul>
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1820 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1821 Note that this transformation makes code much less readable, so it should
1822 only be used in situations where the 'strip' utility would be used, such as
1823 reducing code size or making it harder to reverse engineer code.
1824 </p>
1825</div>
1826
1827<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1828<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1829 <a name="strip-nondebug">-strip-nondebug: Strip all symbols, except dbg symbols, from a module</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1830</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1831<div>
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1832 <p>This pass implements code stripping. Specifically, it can delete:</p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1833 <ul>
1834 <li>names for virtual registers</li>
1835 <li>symbols for internal globals and functions</li>
1836 <li>debug information</li>
1837 </ul>
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1838 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1839 Note that this transformation makes code much less readable, so it should
1840 only be used in situations where the 'strip' utility would be used, such as
1841 reducing code size or making it harder to reverse engineer code.
1842 </p>
1843</div>
1844
1845<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1846<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1847 <a name="tailcallelim">-tailcallelim: Tail Call Elimination</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1848</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1849<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1850 <p>
1851 This file transforms calls of the current function (self recursion) followed
1852 by a return instruction with a branch to the entry of the function, creating
1853 a loop. This pass also implements the following extensions to the basic
1854 algorithm:
1855 </p>
1856
1857 <ul>
1858 <li>Trivial instructions between the call and return do not prevent the
1859 transformation from taking place, though currently the analysis cannot
1860 support moving any really useful instructions (only dead ones).
1861 <li>This pass transforms functions that are prevented from being tail
1862 recursive by an associative expression to use an accumulator variable,
1863 thus compiling the typical naive factorial or <tt>fib</tt> implementation
1864 into efficient code.
1865 <li>TRE is performed if the function returns void, if the return
1866 returns the result returned by the call, or if the function returns a
1867 run-time constant on all exits from the function. It is possible, though
1868 unlikely, that the return returns something else (like constant 0), and
1869 can still be TRE'd. It can be TRE'd if <em>all other</em> return
1870 instructions in the function return the exact same value.
1871 <li>If it can prove that callees do not access theier caller stack frame,
1872 they are marked as eligible for tail call elimination (by the code
1873 generator).
1874 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1875</div>
1876
1877<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1878<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1879 <a name="tailduplicate">-tailduplicate: Tail Duplication</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1880</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1881<div>
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1882 <p>
1883 This pass performs a limited form of tail duplication, intended to simplify
1884 CFGs by removing some unconditional branches. This pass is necessary to
1885 straighten out loops created by the C front-end, but also is capable of
1886 making other code nicer. After this pass is run, the CFG simplify pass
1887 should be run to clean up the mess.
1888 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1889</div>
1890
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1891</div>
1892
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1893<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1894<h2><a name="utilities">Utility Passes</a></h2>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1895<div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1896 <p>This section describes the LLVM Utility Passes.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1897
1898<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1899<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1900 <a name="deadarghaX0r">-deadarghaX0r: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1901</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1902<div>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1903 <p>
1904 Same as dead argument elimination, but deletes arguments to functions which
1905 are external. This is only for use by <a
1906 href="Bugpoint.html">bugpoint</a>.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1907</div>
1908
1909<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1910<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1911 <a name="extract-blocks">-extract-blocks: Extract Basic Blocks From Module (for bugpoint use)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1912</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1913<div>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1914 <p>
1915 This pass is used by bugpoint to extract all blocks from the module into their
1916 own functions.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1917</div>
1918
1919<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1920<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1921 <a name="instnamer">-instnamer: Assign names to anonymous instructions</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1922</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1923<div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1924 <p>This is a little utility pass that gives instructions names, this is mostly
1925 useful when diffing the effect of an optimization because deleting an
1926 unnamed instruction can change all other instruction numbering, making the
1927 diff very noisy.
1928 </p>
1929</div>
1930
1931<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1932<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1933 <a name="preverify">-preverify: Preliminary module verification</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1934</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1935<div>
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]1936 <p>
1937 Ensures that the module is in the form required by the <a
1938 href="#verifier">Module Verifier</a> pass.
1939 </p>
1940
1941 <p>
1942 Running the verifier runs this pass automatically, so there should be no need
1943 to use it directly.
1944 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1945</div>
1946
1947<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1948<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1949 <a name="verify">-verify: Module Verifier</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1950</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1951<div>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1952 <p>
1953 Verifies an LLVM IR code. This is useful to run after an optimization which is
1954 undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
1955 emitting bitcode, and also that malformed bitcode is likely to make LLVM
1956 crash. All language front-ends are therefore encouraged to verify their output
1957 before performing optimizing transformations.
1958 </p>
1959
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1960 <ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1961 <li>Both of a binary operator's parameters are of the same type.</li>
1962 <li>Verify that the indices of mem access instructions match other
1963 operands.</li>
1964 <li>Verify that arithmetic and other things are only performed on
1965 first-class types. Verify that shifts and logicals only happen on
1966 integrals f.e.</li>
1967 <li>All of the constants in a switch statement are of the correct type.</li>
1968 <li>The code is in valid SSA form.</li>
Chris Lattner46b3abc2009-10-28 04:47:06 +0000[diff] [blame]1969 <li>It is illegal to put a label into any other type (like a structure) or
1970 to return one.</li>
Nick Lewycky0c78ac12008-03-28 06:46:51 +0000[diff] [blame]1971 <li>Only phi nodes can be self referential: <tt>%x = add i32 %x, %x</tt> is
Gordon Henriksen873390e2007-11-04 18:17:58 +0000[diff] [blame]1972 invalid.</li>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1973 <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
1974 <li>PHI nodes must be the first thing in a basic block, all grouped
1975 together.</li>
1976 <li>PHI nodes must have at least one entry.</li>
1977 <li>All basic blocks should only end with terminator insts, not contain
1978 them.</li>
1979 <li>The entry node to a function must not have predecessors.</li>
1980 <li>All Instructions must be embedded into a basic block.</li>
1981 <li>Functions cannot take a void-typed parameter.</li>
1982 <li>Verify that a function's argument list agrees with its declared
1983 type.</li>
1984 <li>It is illegal to specify a name for a void value.</li>
1985 <li>It is illegal to have a internal global value with no initializer.</li>
1986 <li>It is illegal to have a ret instruction that returns a value that does
1987 not agree with the function return value type.</li>
1988 <li>Function call argument types match the function prototype.</li>
1989 <li>All other things that are tested by asserts spread about the code.</li>
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1990 </ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1991
1992 <p>
1993 Note that this does not provide full security verification (like Java), but
1994 instead just tries to ensure that code is well-formed.
1995 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1996</div>
1997
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1998<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1999<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2000 <a name="view-cfg">-view-cfg: View CFG of function</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2001</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2002<div>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2003 <p>
2004 Displays the control flow graph using the GraphViz tool.
2005 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2006</div>
2007
2008<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2009<h3>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2010 <a name="view-cfg-only">-view-cfg-only: View CFG of function (with no function bodies)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2011</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2012<div>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2013 <p>
2014 Displays the control flow graph using the GraphViz tool, but omitting function
2015 bodies.
2016 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2017</div>
2018
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2019<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2020<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]2021 <a name="view-dom">-view-dom: View dominance tree of function</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2022</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2023<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2024 <p>
2025 Displays the dominator tree using the GraphViz tool.
2026 </p>
2027</div>
2028
2029<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2030<h3>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]2031 <a name="view-dom-only">-view-dom-only: View dominance tree of function (with no function bodies)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2032</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2033<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2034 <p>
2035 Displays the dominator tree using the GraphViz tool, but omitting function
2036 bodies.
2037 </p>
2038</div>
2039
2040<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2041<h3>
Eli Friedmane6ed15b2011-03-19 04:47:52 +0000[diff] [blame]2042 <a name="view-postdom">-view-postdom: View postdominance tree of function</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2043</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2044<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2045 <p>
2046 Displays the post dominator tree using the GraphViz tool.
2047 </p>
2048</div>
2049
2050<!-------------------------------------------------------------------------- -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2051<h3>
Eli Friedman415247d2011-03-19 05:02:14 +0000[diff] [blame]2052 <a name="view-postdom-only">-view-postdom-only: View postdominance tree of function (with no function bodies)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2053</h3>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2054<div>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2055 <p>
2056 Displays the post dominator tree using the GraphViz tool, but omitting
2057 function bodies.
2058 </p>
2059</div>
2060
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2061</div>
2062
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2063<!-- *********************************************************************** -->
2064
2065<hr>
2066<address>
2067 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]2068 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2069 <a href="http://validator.w3.org/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]2070 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2071
2072 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000[diff] [blame]2073 <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2074 Last modified: $Date$
2075</address>
2076
2077</body>
2078</html>