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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / f96b0063674e6bf72da5429bd49097e33c2325c7 / . / docs / Passes.html
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Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]43<div class="doc_title">LLVM's Analysis and Transform Passes</div>
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<!-- ======================================================================= -->
58<div class="doc_section"> <a name="intro">Introduction</a> </div>
59<div class="doc_text">
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>
72</div>
73<div class="doc_text" >
74<table>
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]75<tr><th colspan="2"><b>ANALYSIS PASSES</b></th></tr>
76<tr><th>Option</th><th>Name</th></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]77<tr><td><a href="#aa-eval">-aa-eval</a></td><td>Exhaustive Alias Analysis Precision Evaluator</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]78<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (default AA impl)</td></tr>
79<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]80<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]81<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
82<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
83<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]84<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]85<tr><td><a href="#dot-callgraph">-dot-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
86<tr><td><a href="#dot-cfg">-dot-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
87<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>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]88<tr><td><a href="#dot-dom">-dot-dom</a></td><td>Print dominator tree of function to 'dot' file</td></tr>
89<tr><td><a href="#dot-dom-only">-dot-dom-only</a></td><td>Print dominator tree of function to 'dot' file (with no function bodies)</td></tr>
90<tr><td><a href="#dot-postdom">-dot-postdom</a></td><td>Print post dominator tree of function to 'dot' file</td></tr>
91<tr><td><a href="#dot-postdom-only">-dot-postdom-only</a></td><td>Print post dominator tree of function to 'dot' file (with no function bodies)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]92<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]93<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]94<tr><td><a href="#interprocedural-aa-eval">-interprocedural-aa-eval</a></td><td>Exhaustive Interprocedural Alias Analysis Precision Evaluator</td></tr>
95<tr><td><a href="#interprocedural-basic-aa">-interprocedural-basic-aa</a></td><td>Interprocedural Basic Alias Analysis</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]96<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]97<tr><td><a href="#iv-users">-iv-users</a></td><td>Induction Variable Users</td></tr>
98<tr><td><a href="#lazy-value-info">-lazy-value-info</a></td><td>Lazy Value Information Analysis</td></tr>
99<tr><td><a href="#lda">-lda</a></td><td>Loop Dependence Analysis</td></tr>
100<tr><td><a href="#libcall-aa">-libcall-aa</a></td><td>LibCall Alias Analysis</td></tr>
101<tr><td><a href="#lint">-lint</a></td><td>Check for common errors in LLVM IR</td></tr>
102<tr><td><a href="#live-values">-live-values</a></td><td>Value Liveness Analysis</td></tr>
103<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Information</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]104<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]105<tr><td><a href="#module-debuginfo">-module-debuginfo</a></td><td>Prints module debug info metadata</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]106<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
107<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]108<tr><td><a href="#pointertracking">-pointertracking</a></td><td>Track pointer bounds</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]109<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]110<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]111<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]112<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
113<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
114<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]115<tr><td><a href="#print-dbginfo">-print-dbginfo</a></td><td>Print debug info in human readable form</td></tr>
116<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]117<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
118<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
119<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
120<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]121<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]122<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
Tobias Grosserf96b0062010-07-22 07:46:31 +0000[diff] [blame^]123<tr><td><a href="#regions">-regions</a></td><td>Detect single entry single exit regions in a function</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]124<tr><td><a href="#profile-verifier">-profile-verifier</a></td><td>Verify profiling information</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]125<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]126<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]127<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
128
129
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]130<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
131<tr><th>Option</th><th>Name</th></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]132<tr><td><a href="#abcd">-abcd</a></td><td>Remove redundant conditional branches</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]133<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]134<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]135<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
136<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]137<tr><td><a href="#break-crit-edges">-break-crit-edges</a></td><td>Break critical edges in CFG</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]138<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Prepare a function for code generation </td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]139<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
140<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
141<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
142<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
143<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
144<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
145<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]146<tr><td><a href="#functionattrs">-functionattrs</a></td><td>Deduce function attributes</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]147<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
148<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]149<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]150<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
151<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]152<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]153<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]154<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
155<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
156<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
157<tr><td><a href="#ipsccp">-ipsccp</a></td><td>Interprocedural Sparse Conditional Constant Propagation</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]158<tr><td><a href="#jump-threading">-jump-threading</a></td><td>Thread control through conditional blocks </td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]159<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
160<tr><td><a href="#licm">-licm</a></td><td>Loop Invariant Code Motion</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]161<tr><td><a href="#loop-deletion">-loop-deletion</a></td><td>Dead Loop Deletion Pass </td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]162<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
163<tr><td><a href="#loop-extract-single">-loop-extract-single</a></td><td>Extract at most one loop into a new function</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]164<tr><td><a href="#loop-index-split">-loop-index-split</a></td><td>Index Split Loops</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]165<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]166<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
167<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
168<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
169<tr><td><a href="#loopsimplify">-loopsimplify</a></td><td>Canonicalize natural loops</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]170<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]171<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
172<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
173<tr><td><a href="#mem2reg">-mem2reg</a></td><td>Promote Memory to Register</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]174<tr><td><a href="#memcpyopt">-memcpyopt</a></td><td>Optimize use of memcpy and friends</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]175<tr><td><a href="#mergefunc">-mergefunc</a></td><td>Merge Functions</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]176<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]177<tr><td><a href="#partial-inliner">-partial-inliner</a></td><td>Partial Inliner</td></tr>
178<tr><td><a href="#partialspecialization">-partialspecialization</a></td><td>Partial Specialization</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]179<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]180<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
181<tr><td><a href="#reg2mem">-reg2mem</a></td><td>Demote all values to stack slots</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]182<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates</td></tr>
183<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]184<tr><td><a href="#sink">-sink</a></td><td>Code Sinking</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]185<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]186<tr><td><a href="#simplify-libcalls-halfpowr">-simplify-libcalls-halfpowr</a></td><td>Simplify half_powr library calls</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]187<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]188<tr><td><a href="#split-geps">-split-geps</a></td><td>Split complex GEPs into simple GEPs</td></tr>
189<tr><td><a href="#ssi">-ssi</a></td><td>Static Single Information Construction</td></tr>
190<tr><td><a href="#ssi-everything">-ssi-everything</a></td><td>Static Single Information Construction (everything, intended for debugging)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]191<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]192<tr><td><a href="#strip-dead-debug-info">-strip-dead-debug-info</a></td><td>Strip debug info for unused symbols</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]193<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Remove unused function declarations</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]194<tr><td><a href="#strip-debug-declare">-strip-debug-declare</a></td><td>Strip all llvm.dbg.declare intrinsics</td></tr>
195<tr><td><a href="#strip-nondebug">-strip-nondebug</a></td><td>Strip all symbols, except dbg symbols, from a module</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]196<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]197<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
198<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]199
200
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]201<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
202<tr><th>Option</th><th>Name</th></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]203<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
204<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]205<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]206<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]207<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]208<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
209<tr><td><a href="#view-cfg-only">-view-cfg-only</a></td><td>View CFG of function (with no function bodies)</td></tr>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]210<tr><td><a href="#view-dom">-view-dom</a></td><td>View dominator tree of function</td></tr>
211<tr><td><a href="#view-dom-only">-view-dom-only</a></td><td>View dominator tree of function (with no function bodies)</td></tr>
212<tr><td><a href="#view-postdom">-view-postdom</a></td><td>View post dominator tree of function</td></tr>
213<tr><td><a href="#view-postdom-only">-view-postdom-only</a></td><td>View post dominator tree of function (with no function bodies)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]214</table>
215</div>
216
217<!-- ======================================================================= -->
218<div class="doc_section"> <a name="example">Analysis Passes</a></div>
219<div class="doc_text">
220 <p>This section describes the LLVM Analysis Passes.</p>
221</div>
222
223<!-------------------------------------------------------------------------- -->
224<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]225 <a name="aa-eval">-aa-eval: Exhaustive Alias Analysis Precision Evaluator</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]226</div>
227<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]228 <p>This is a simple N^2 alias analysis accuracy evaluator.
229 Basically, for each function in the program, it simply queries to see how the
230 alias analysis implementation answers alias queries between each pair of
231 pointers in the function.</p>
232
233 <p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
234 Spadini, and Wojciech Stryjewski.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]235</div>
236
237<!-------------------------------------------------------------------------- -->
238<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]239 <a name="basicaa">-basicaa: Basic Alias Analysis (default AA impl)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]240</div>
241<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]242 <p>
243 This is the default implementation of the Alias Analysis interface
244 that simply implements a few identities (two different globals cannot alias,
245 etc), but otherwise does no analysis.
246 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]247</div>
248
249<!-------------------------------------------------------------------------- -->
250<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]251 <a name="basiccg">-basiccg: Basic CallGraph Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]252</div>
253<div class="doc_text">
254 <p>Yet to be written.</p>
255</div>
256
257<!-------------------------------------------------------------------------- -->
258<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]259 <a name="codegenprepare">-codegenprepare: Optimize for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]260</div>
261<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]262 <p>
263 This pass munges the code in the input function to better prepare it for
264 SelectionDAG-based code generation. This works around limitations in it's
265 basic-block-at-a-time approach. It should eventually be removed.
266 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]267</div>
268
269<!-------------------------------------------------------------------------- -->
270<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]271 <a name="count-aa">-count-aa: Count Alias Analysis Query Responses</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]272</div>
273<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]274 <p>
275 A pass which can be used to count how many alias queries
276 are being made and how the alias analysis implementation being used responds.
277 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]278</div>
279
280<!-------------------------------------------------------------------------- -->
281<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]282 <a name="debug-aa">-debug-aa: AA use debugger</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]283</div>
284<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]285 <p>
286 This simple pass checks alias analysis users to ensure that if they
287 create a new value, they do not query AA without informing it of the value.
288 It acts as a shim over any other AA pass you want.
289 </p>
290
291 <p>
292 Yes keeping track of every value in the program is expensive, but this is
293 a debugging pass.
294 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]295</div>
296
297<!-------------------------------------------------------------------------- -->
298<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]299 <a name="domfrontier">-domfrontier: Dominance Frontier Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]300</div>
301<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]302 <p>
303 This pass is a simple dominator construction algorithm for finding forward
304 dominator frontiers.
305 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]306</div>
307
308<!-------------------------------------------------------------------------- -->
309<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]310 <a name="domtree">-domtree: Dominator Tree Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]311</div>
312<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]313 <p>
314 This pass is a simple dominator construction algorithm for finding forward
315 dominators.
316 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]317</div>
318
319<!-------------------------------------------------------------------------- -->
320<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]321 <a name="dot-callgraph">-dot-callgraph: Print Call Graph to 'dot' file</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]322</div>
323<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]324 <p>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]325 This pass, only available in <code>opt</code>, prints the call graph into a
326 <code>.dot</code> graph. This graph can then be processed with the "dot" tool
327 to convert it to postscript or some other suitable format.
328 </p>
329</div>
330
331<!-------------------------------------------------------------------------- -->
332<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]333 <a name="dot-cfg">-dot-cfg: Print CFG of function to 'dot' file</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]334</div>
335<div class="doc_text">
336 <p>
337 This pass, only available in <code>opt</code>, prints the control flow graph
338 into a <code>.dot</code> graph. This graph can then be processed with the
339 "dot" tool to convert it to postscript or some other suitable format.
340 </p>
341</div>
342
343<!-------------------------------------------------------------------------- -->
344<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]345 <a name="dot-cfg-only">-dot-cfg-only: Print CFG of function to 'dot' file (with no function bodies)</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]346</div>
347<div class="doc_text">
348 <p>
349 This pass, only available in <code>opt</code>, prints the control flow graph
350 into a <code>.dot</code> graph, omitting the function bodies. This graph can
351 then be processed with the "dot" tool to convert it to postscript or some
352 other suitable format.
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]353 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]354</div>
355
356<!-------------------------------------------------------------------------- -->
357<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]358 <a name="dot-dom">-dot-dom: Print dominator tree of function to 'dot' file</a>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]359</div>
360<div class="doc_text">
361 <p>
362 This pass, only available in <code>opt</code>, prints the dominator tree
363 into a <code>.dot</code> graph. This graph can then be processed with the
364 "dot" tool to convert it to postscript or some other suitable format.
365 </p>
366</div>
367
368<!-------------------------------------------------------------------------- -->
369<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]370 <a name="dot-dom-only">-dot-dom-only: Print dominator tree of function to 'dot' file (with no
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]371 function bodies)</a>
372</div>
373<div class="doc_text">
374 <p>
375 This pass, only available in <code>opt</code>, prints the 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<!-------------------------------------------------------------------------- -->
383<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]384 <a name="dot-postdom">dot-postdom: Print post dominator tree of function to 'dot' file</a>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]385</div>
386<div class="doc_text">
387 <p>
388 This pass, only available in <code>opt</code>, prints the post dominator tree
389 into a <code>.dot</code> graph. This graph can then be processed with the
390 "dot" tool to convert it to postscript or some other suitable format.
391 </p>
392</div>
393
394<!-------------------------------------------------------------------------- -->
395<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]396 <a name="dot-postdom-only">dot-postdom-only: Print post dominator tree of function to 'dot' file
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]397 (with no function bodies)</a>
398</div>
399<div class="doc_text">
400 <p>
401 This pass, only available in <code>opt</code>, prints the post dominator tree
402 into a <code>.dot</code> graph, omitting the function bodies. This graph can
403 then be processed with the "dot" tool to convert it to postscript or some
404 other suitable format.
405 </p>
406</div>
407
408<!-------------------------------------------------------------------------- -->
409<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]410 <a name="globalsmodref-aa">-globalsmodref-aa: Simple mod/ref analysis for globals</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]411</div>
412<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]413 <p>
414 This simple pass provides alias and mod/ref information for global values
415 that do not have their address taken, and keeps track of whether functions
416 read or write memory (are "pure"). For this simple (but very common) case,
417 we can provide pretty accurate and useful information.
418 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]419</div>
420
421<!-------------------------------------------------------------------------- -->
422<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]423 <a name="instcount">-instcount: Counts the various types of Instructions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]424</div>
425<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]426 <p>
427 This pass collects the count of all instructions and reports them
428 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]429</div>
430
431<!-------------------------------------------------------------------------- -->
432<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]433 <a name="interprocedural-aa-eval">-interprocedural-aa-eval: Exhaustive Interprocedural Alias Analysis Precision Evaluator</a>
434</div>
435<div class="doc_text">
436 <p>This pass implements a simple N^2 alias analysis accuracy evaluator.
437 Basically, for each function in the program, it simply queries to see how the
438 alias analysis implementation answers alias queries between each pair of
439 pointers in the function.
440 </p>
441</div>
442
443<!-------------------------------------------------------------------------- -->
444<div class="doc_subsection">
445 <a name="interprocedural-basic-aa">-interprocedural-basic-aa: Interprocedural Basic Alias Analysis</a>
446</div>
447<div class="doc_text">
448 <p>This pass defines the default implementation of the Alias Analysis interface
449 that simply implements a few identities (two different globals cannot alias,
450 etc), but otherwise does no analysis.
451 </p>
452</div>
453
454<!-------------------------------------------------------------------------- -->
455<div class="doc_subsection">
456 <a name="intervals">-intervals: Interval Partition Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]457</div>
458<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]459 <p>
460 This analysis calculates and represents the interval partition of a function,
461 or a preexisting interval partition.
462 </p>
463
464 <p>
465 In this way, the interval partition may be used to reduce a flow graph down
466 to its degenerate single node interval partition (unless it is irreducible).
467 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]468</div>
469
470<!-------------------------------------------------------------------------- -->
471<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]472 <a name="iv-users">-iv-users: Induction Variable Users</a>
473</div>
474<div class="doc_text">
475 <p>Bookkeeping for "interesting" users of expressions computed from
476 induction variables.</p>
477</div>
478
479<!-------------------------------------------------------------------------- -->
480<div class="doc_subsection">
481 <a name="lazy-value-info">-lazy-value-info: Lazy Value Information Analysis</a>
482</div>
483<div class="doc_text">
484 <p>Interface for lazy computation of value constraint information.</p>
485</div>
486
487<!-------------------------------------------------------------------------- -->
488<div class="doc_subsection">
489 <a name="lda">-lda: Loop Dependence Analysis</a>
490</div>
491<div class="doc_text">
492 <p>Loop dependence analysis framework, which is used to detect dependences in
493 memory accesses in loops.</p>
494</div>
495
496<!-------------------------------------------------------------------------- -->
497<div class="doc_subsection">
498 <a name="libcall-aa">-libcall-aa: LibCall Alias Analysis</a>
499</div>
500<div class="doc_text">
501 <p>LibCall Alias Analysis.</p>
502</div>
503
504<!-------------------------------------------------------------------------- -->
505<div class="doc_subsection">
506 <a name="lint">-lint: Check for common errors in LLVM IR</a>
507</div>
508<div class="doc_text">
509 <p>This pass statically checks for common and easily-identified constructs
510 which produce undefined or likely unintended behavior in LLVM IR.</p>
511
512 <p>It is not a guarantee of correctness, in two ways. First, it isn't
513 comprehensive. There are checks which could be done statically which are
514 not yet implemented. Some of these are indicated by TODO comments, but
515 those aren't comprehensive either. Second, many conditions cannot be
516 checked statically. This pass does no dynamic instrumentation, so it
517 can't check for all possible problems.</p>
518
519 <p>Another limitation is that it assumes all code will be executed. A store
520 through a null pointer in a basic block which is never reached is harmless,
521 but this pass will warn about it anyway.</p>
522
523 <p>Optimization passes may make conditions that this pass checks for more or
524 less obvious. If an optimization pass appears to be introducing a warning,
525 it may be that the optimization pass is merely exposing an existing
526 condition in the code.</p>
527
528 <p>This code may be run before instcombine. In many cases, instcombine checks
529 for the same kinds of things and turns instructions with undefined behavior
530 into unreachable (or equivalent). Because of this, this pass makes some
531 effort to look through bitcasts and so on.
532 </p>
533</div>
534
535<!-------------------------------------------------------------------------- -->
536<div class="doc_subsection">
537 <a name="live-values">-live-values: Values Liveness Analysis</a>
538</div>
539<div class="doc_text">
540 <p>LLVM IR Value liveness analysis pass.</p>
541</div>
542
543<!-------------------------------------------------------------------------- -->
544<div class="doc_subsection">
545 <a name="loops">-loops: Natural Loop Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]546</div>
547<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]548 <p>
549 This analysis is used to identify natural loops and determine the loop depth
550 of various nodes of the CFG. Note that the loops identified may actually be
551 several natural loops that share the same header node... not just a single
552 natural loop.
553 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]554</div>
555
556<!-------------------------------------------------------------------------- -->
557<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]558 <a name="memdep">-memdep: Memory Dependence Analysis</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]559</div>
560<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]561 <p>
562 An analysis that determines, for a given memory operation, what preceding
563 memory operations it depends on. It builds on alias analysis information, and
564 tries to provide a lazy, caching interface to a common kind of alias
565 information query.
566 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]567</div>
568
569<!-------------------------------------------------------------------------- -->
570<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]571 <a name="module-debuginfo">-module-debuginfo: Prints module debug info metadata</a>
572</div>
573<div class="doc_text">
574 <p>This pass decodes the debug info metadata in a module and prints in a
575 (sufficiently-prepared-) human-readable form.
576
577 For example, run this pass from opt along with the -analyze option, and
578 it'll print to standard output.
579 </p>
580</div>
581
582<!-------------------------------------------------------------------------- -->
583<div class="doc_subsection">
584 <a name="no-aa">-no-aa: No Alias Analysis (always returns 'may' alias)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]585</div>
586<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]587 <p>
588 Always returns "I don't know" for alias queries. NoAA is unlike other alias
589 analysis implementations, in that it does not chain to a previous analysis. As
590 such it doesn't follow many of the rules that other alias analyses must.
591 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]592</div>
593
594<!-------------------------------------------------------------------------- -->
595<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]596 <a name="no-profile">-no-profile: No Profile Information</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]597</div>
598<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]599 <p>
600 The default "no profile" implementation of the abstract
601 <code>ProfileInfo</code> interface.
602 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]603</div>
604
605<!-------------------------------------------------------------------------- -->
606<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]607 <a name="pointertracking">-pointertracking: Track pointer bounds.</a>
608</div>
609<div class="doc_text">
610 <p>Tracking of pointer bounds.
611 </p>
612</div>
613
614<!-------------------------------------------------------------------------- -->
615<div class="doc_subsection">
616 <a name="postdomfrontier">-postdomfrontier: Post-Dominance Frontier Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]617</div>
618<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]619 <p>
620 This pass is a simple post-dominator construction algorithm for finding
621 post-dominator frontiers.
622 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]623</div>
624
625<!-------------------------------------------------------------------------- -->
626<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]627 <a name="postdomtree">-postdomtree: Post-Dominator Tree Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]628</div>
629<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]630 <p>
631 This pass is a simple post-dominator construction algorithm for finding
632 post-dominators.
633 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]634</div>
635
636<!-------------------------------------------------------------------------- -->
637<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]638 <a name="print-alias-sets">-print-alias-sets: Alias Set Printer</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]639</div>
640<div class="doc_text">
641 <p>Yet to be written.</p>
642</div>
643
644<!-------------------------------------------------------------------------- -->
645<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]646 <a name="print-callgraph">-print-callgraph: Print a call graph</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]647</div>
648<div class="doc_text">
649 <p>
650 This pass, only available in <code>opt</code>, prints the call graph to
651 standard output in a human-readable form.
652 </p>
653</div>
654
655<!-------------------------------------------------------------------------- -->
656<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]657 <a name="print-callgraph-sccs">-print-callgraph-sccs: Print SCCs of the Call Graph</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]658</div>
659<div class="doc_text">
660 <p>
661 This pass, only available in <code>opt</code>, prints the SCCs of the call
662 graph to standard output in a human-readable form.
663 </p>
664</div>
665
666<!-------------------------------------------------------------------------- -->
667<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]668 <a name="print-cfg-sccs">-print-cfg-sccs: Print SCCs of each function CFG</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]669</div>
670<div class="doc_text">
671 <p>
672 This pass, only available in <code>opt</code>, prints the SCCs of each
673 function CFG to standard output in a human-readable form.
674 </p>
675</div>
676
677<!-------------------------------------------------------------------------- -->
678<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]679 <a name="print-dbginfo">-print-dbginfo: Print debug info in human readable form</a>
680</div>
681<div class="doc_text">
682 <p>Pass that prints instructions, and associated debug info:
683 <ul>
684
685 <li>source/line/col information</li>
686 <li>original variable name</li>
687 <li>original type name</li>
688 </ul>
689
690 </p>
691</div>
692
693<!-------------------------------------------------------------------------- -->
694<div class="doc_subsection">
695 <a name="print-dom-info">-print-dom-info: Dominator Info Printer</a>
696</div>
697<div class="doc_text">
698 <p>Dominator Info Printer.</p>
699</div>
700
701<!-------------------------------------------------------------------------- -->
702<div class="doc_subsection">
703 <a name="print-externalfnconstants">-print-externalfnconstants: Print external fn callsites passed constants</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]704</div>
705<div class="doc_text">
706 <p>
707 This pass, only available in <code>opt</code>, prints out call sites to
708 external functions that are called with constant arguments. This can be
709 useful when looking for standard library functions we should constant fold
710 or handle in alias analyses.
711 </p>
712</div>
713
714<!-------------------------------------------------------------------------- -->
715<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]716 <a name="print-function">-print-function: Print function to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]717</div>
718<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]719 <p>
720 The <code>PrintFunctionPass</code> class is designed to be pipelined with
721 other <code>FunctionPass</code>es, and prints out the functions of the module
722 as they are processed.
723 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]724</div>
725
726<!-------------------------------------------------------------------------- -->
727<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]728 <a name="print-module">-print-module: Print module to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]729</div>
730<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]731 <p>
732 This pass simply prints out the entire module when it is executed.
733 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]734</div>
735
736<!-------------------------------------------------------------------------- -->
737<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]738 <a name="print-used-types">-print-used-types: Find Used Types</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]739</div>
740<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]741 <p>
742 This pass is used to seek out all of the types in use by the program. Note
743 that this analysis explicitly does not include types only used by the symbol
744 table.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]745</div>
746
747<!-------------------------------------------------------------------------- -->
748<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]749 <a name="profile-estimator">-profile-estimator: Estimate profiling information</a>
750</div>
751<div class="doc_text">
752 <p>Profiling information that estimates the profiling information
753 in a very crude and unimaginative way.
754 </p>
755</div>
756
757<!-------------------------------------------------------------------------- -->
758<div class="doc_subsection">
759 <a name="profile-loader">-profile-loader: Load profile information from llvmprof.out</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]760</div>
761<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]762 <p>
763 A concrete implementation of profiling information that loads the information
764 from a profile dump file.
765 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]766</div>
767
768<!-------------------------------------------------------------------------- -->
769<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]770 <a name="profile-verifier">-profile-verifier: Verify profiling information</a>
771</div>
772<div class="doc_text">
773 <p>Pass that checks profiling information for plausibility.</p>
774</div>
Tobias Grosserf96b0062010-07-22 07:46:31 +0000[diff] [blame^]775<div class="doc_subsection">
776 <a name="regions">-regions: Detect single entry single exit regions in a function</a>
777</div>
778<div class="doc_text">
779 <p>
780 The <code>RegionInfo</code> pass detects single entry single exit regions in a
781 function, where a region is defined as any subgraph that is connected to the
782 remaining graph at only two spots. Furthermore, an hierarchical region tree is
783 built.
784 </p>
785</div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]786
787<!-------------------------------------------------------------------------- -->
788<div class="doc_subsection">
789 <a name="scalar-evolution">-scalar-evolution: Scalar Evolution Analysis</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]790</div>
791<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]792 <p>
793 The <code>ScalarEvolution</code> analysis can be used to analyze and
794 catagorize scalar expressions in loops. It specializes in recognizing general
795 induction variables, representing them with the abstract and opaque
796 <code>SCEV</code> class. Given this analysis, trip counts of loops and other
797 important properties can be obtained.
798 </p>
799
800 <p>
801 This analysis is primarily useful for induction variable substitution and
802 strength reduction.
803 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]804</div>
805
806<!-------------------------------------------------------------------------- -->
807<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]808 <a name="scev-aa">-scev-aa: </a>
809</div>
810<div class="doc_text">
811 <p>Simple alias analysis implemented in terms of ScalarEvolution queries.
812
813 This differs from traditional loop dependence analysis in that it tests
814 for dependencies within a single iteration of a loop, rather than
815 dependencies between different iterations.
816
817 ScalarEvolution has a more complete understanding of pointer arithmetic
818 than BasicAliasAnalysis' collection of ad-hoc analyses.
819 </p>
820</div>
821
822<!-------------------------------------------------------------------------- -->
823<div class="doc_subsection">
824 <a name="strip-dead-debug-info">-strip-dead-debug-info: Strip debug info for unused symbols</a>
825</div>
826<div class="doc_text">
827 <p>
828 performs code stripping. this transformation can delete:
829 </p>
830
831 <ol>
832 <li>names for virtual registers</li>
833 <li>symbols for internal globals and functions</li>
834 <li>debug information</li>
835 </ol>
836
837 <p>
838 note that this transformation makes code much less readable, so it should
839 only be used in situations where the <tt>strip</tt> utility would be used,
840 such as reducing code size or making it harder to reverse engineer code.
841 </p>
842</div>
843
844<!-------------------------------------------------------------------------- -->
845<div class="doc_subsection">
846 <a name="targetdata">-targetdata: Target Data Layout</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]847</div>
848<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]849 <p>Provides other passes access to information on how the size and alignment
850 required by the the target ABI for various data types.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]851</div>
852
853<!-- ======================================================================= -->
854<div class="doc_section"> <a name="transform">Transform Passes</a></div>
855<div class="doc_text">
856 <p>This section describes the LLVM Transform Passes.</p>
857</div>
858
859<!-------------------------------------------------------------------------- -->
860<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]861 <a name="abcd">-abcd: Remove redundant conditional branches</a>
862</div>
863<div class="doc_text">
864 <p>ABCD removes conditional branch instructions that can be proved redundant.
865 With the SSI representation, each variable has a constraint. By analyzing these
866 constraints we can prove that a branch is redundant. When a branch is proved
867 redundant it means that one direction will always be taken; thus, we can change
868 this branch into an unconditional jump.</p>
869 <p>It is advisable to run <a href="#simplifycfg">SimplifyCFG</a> and
870 <a href="#adce">Aggressive Dead Code Elimination</a> after ABCD
871 to clean up the code.</p>
872</div>
873
874<!-------------------------------------------------------------------------- -->
875<div class="doc_subsection">
876 <a name="adce">-adce: Aggressive Dead Code Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]877</div>
878<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]879 <p>ADCE aggressively tries to eliminate code. This pass is similar to
880 <a href="#dce">DCE</a> but it assumes that values are dead until proven
881 otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
882 the liveness of values.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]883</div>
884
885<!-------------------------------------------------------------------------- -->
886<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]887 <a name="always-inline">-always-inline: Inliner for always_inline functions</a>
888</div>
889<div class="doc_text">
890 <p>A custom inliner that handles only functions that are marked as
891 "always inline".</p>
892</div>
893
894<!-------------------------------------------------------------------------- -->
895<div class="doc_subsection">
896 <a name="argpromotion">-argpromotion: Promote 'by reference' arguments to scalars</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]897</div>
898<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]899 <p>
900 This pass promotes "by reference" arguments to be "by value" arguments. In
901 practice, this means looking for internal functions that have pointer
902 arguments. If it can prove, through the use of alias analysis, that an
903 argument is *only* loaded, then it can pass the value into the function
904 instead of the address of the value. This can cause recursive simplification
905 of code and lead to the elimination of allocas (especially in C++ template
906 code like the STL).
907 </p>
908
909 <p>
910 This pass also handles aggregate arguments that are passed into a function,
911 scalarizing them if the elements of the aggregate are only loaded. Note that
912 it refuses to scalarize aggregates which would require passing in more than
913 three operands to the function, because passing thousands of operands for a
914 large array or structure is unprofitable!
915 </p>
916
917 <p>
918 Note that this transformation could also be done for arguments that are only
919 stored to (returning the value instead), but does not currently. This case
920 would be best handled when and if LLVM starts supporting multiple return
921 values from functions.
922 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]923</div>
924
925<!-------------------------------------------------------------------------- -->
926<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]927 <a name="block-placement">-block-placement: Profile Guided Basic Block Placement</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]928</div>
929<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]930 <p>This pass is a very simple profile guided basic block placement algorithm.
931 The idea is to put frequently executed blocks together at the start of the
932 function and hopefully increase the number of fall-through conditional
933 branches. If there is no profile information for a particular function, this
934 pass basically orders blocks in depth-first order.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]935</div>
936
937<!-------------------------------------------------------------------------- -->
938<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]939 <a name="break-crit-edges">-break-crit-edges: Break critical edges in CFG</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]940</div>
941<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]942 <p>
943 Break all of the critical edges in the CFG by inserting a dummy basic block.
944 It may be "required" by passes that cannot deal with critical edges. This
945 transformation obviously invalidates the CFG, but can update forward dominator
946 (set, immediate dominators, tree, and frontier) information.
947 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]948</div>
949
950<!-------------------------------------------------------------------------- -->
951<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]952 <a name="codegenprepare">-codegenprepare: Prepare a function for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]953</div>
954<div class="doc_text">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]955 This pass munges the code in the input function to better prepare it for
956 SelectionDAG-based code generation. This works around limitations in it's
957 basic-block-at-a-time approach. It should eventually be removed.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]958</div>
959
960<!-------------------------------------------------------------------------- -->
961<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]962 <a name="constmerge">-constmerge: Merge Duplicate Global Constants</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]963</div>
964<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]965 <p>
966 Merges duplicate global constants together into a single constant that is
967 shared. This is useful because some passes (ie TraceValues) insert a lot of
968 string constants into the program, regardless of whether or not an existing
969 string is available.
970 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]971</div>
972
973<!-------------------------------------------------------------------------- -->
974<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]975 <a name="constprop">-constprop: Simple constant propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]976</div>
977<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]978 <p>This file implements constant propagation and merging. It looks for
979 instructions involving only constant operands and replaces them with a
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]980 constant value instead of an instruction. For example:</p>
981 <blockquote><pre>add i32 1, 2</pre></blockquote>
982 <p>becomes</p>
983 <blockquote><pre>i32 3</pre></blockquote>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]984 <p>NOTE: this pass has a habit of making definitions be dead. It is a good
985 idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
986 sometime after running this pass.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]987</div>
988
989<!-------------------------------------------------------------------------- -->
990<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]991 <a name="dce">-dce: Dead Code Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]992</div>
993<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]994 <p>
995 Dead code elimination is similar to <a href="#die">dead instruction
996 elimination</a>, but it rechecks instructions that were used by removed
997 instructions to see if they are newly dead.
998 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]999</div>
1000
1001<!-------------------------------------------------------------------------- -->
1002<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1003 <a name="deadargelim">-deadargelim: Dead Argument Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1004</div>
1005<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1006 <p>
1007 This pass deletes dead arguments from internal functions. Dead argument
1008 elimination removes arguments which are directly dead, as well as arguments
1009 only passed into function calls as dead arguments of other functions. This
1010 pass also deletes dead arguments in a similar way.
1011 </p>
1012
1013 <p>
1014 This pass is often useful as a cleanup pass to run after aggressive
1015 interprocedural passes, which add possibly-dead arguments.
1016 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1017</div>
1018
1019<!-------------------------------------------------------------------------- -->
1020<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1021 <a name="deadtypeelim">-deadtypeelim: Dead Type Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1022</div>
1023<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1024 <p>
1025 This pass is used to cleanup the output of GCC. It eliminate names for types
1026 that are unused in the entire translation unit, using the <a
1027 href="#findusedtypes">find used types</a> pass.
1028 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1029</div>
1030
1031<!-------------------------------------------------------------------------- -->
1032<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1033 <a name="die">-die: Dead Instruction Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1034</div>
1035<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1036 <p>
1037 Dead instruction elimination performs a single pass over the function,
1038 removing instructions that are obviously dead.
1039 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1040</div>
1041
1042<!-------------------------------------------------------------------------- -->
1043<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1044 <a name="dse">-dse: Dead Store Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1045</div>
1046<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1047 <p>
1048 A trivial dead store elimination that only considers basic-block local
1049 redundant stores.
1050 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1051</div>
1052
1053<!-------------------------------------------------------------------------- -->
1054<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1055 <a name="functionattrs">-functionattrs: Deduce function attributes</a>
1056</div>
1057<div class="doc_text">
1058 <p>A simple interprocedural pass which walks the call-graph, looking for
1059 functions which do not access or only read non-local memory, and marking them
1060 readnone/readonly. In addition, it marks function arguments (of pointer type)
1061 'nocapture' if a call to the function does not create any copies of the pointer
1062 value that outlive the call. This more or less means that the pointer is only
1063 dereferenced, and not returned from the function or stored in a global.
1064 This pass is implemented as a bottom-up traversal of the call-graph.
1065 </p>
1066</div>
1067
1068<!-------------------------------------------------------------------------- -->
1069<div class="doc_subsection">
1070 <a name="globaldce">-globaldce: Dead Global Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1071</div>
1072<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1073 <p>
1074 This transform is designed to eliminate unreachable internal globals from the
1075 program. It uses an aggressive algorithm, searching out globals that are
1076 known to be alive. After it finds all of the globals which are needed, it
1077 deletes whatever is left over. This allows it to delete recursive chunks of
1078 the program which are unreachable.
1079 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1080</div>
1081
1082<!-------------------------------------------------------------------------- -->
1083<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1084 <a name="globalopt">-globalopt: Global Variable Optimizer</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1085</div>
1086<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1087 <p>
1088 This pass transforms simple global variables that never have their address
1089 taken. If obviously true, it marks read/write globals as constant, deletes
1090 variables only stored to, etc.
1091 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1092</div>
1093
1094<!-------------------------------------------------------------------------- -->
1095<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1096 <a name="gvn">-gvn: Global Value Numbering</a>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]1097</div>
1098<div class="doc_text">
1099 <p>
Chris Lattner60f03402009-10-10 18:40:48 +0000[diff] [blame]1100 This pass performs global value numbering to eliminate fully and partially
1101 redundant instructions. It also performs redundant load elimination.
Matthijs Kooijman845f5242008-06-05 07:55:49 +0000[diff] [blame]1102 </p>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]1103</div>
1104
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1105<!-------------------------------------------------------------------------- -->
1106<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1107 <a name="indvars">-indvars: Canonicalize Induction Variables</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1108</div>
1109<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1110 <p>
1111 This transformation analyzes and transforms the induction variables (and
1112 computations derived from them) into simpler forms suitable for subsequent
1113 analysis and transformation.
1114 </p>
1115
1116 <p>
1117 This transformation makes the following changes to each loop with an
1118 identifiable induction variable:
1119 </p>
1120
1121 <ol>
1122 <li>All loops are transformed to have a <em>single</em> canonical
1123 induction variable which starts at zero and steps by one.</li>
1124 <li>The canonical induction variable is guaranteed to be the first PHI node
1125 in the loop header block.</li>
1126 <li>Any pointer arithmetic recurrences are raised to use array
1127 subscripts.</li>
1128 </ol>
1129
1130 <p>
1131 If the trip count of a loop is computable, this pass also makes the following
1132 changes:
1133 </p>
1134
1135 <ol>
1136 <li>The exit condition for the loop is canonicalized to compare the
1137 induction value against the exit value. This turns loops like:
1138 <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
1139 into
1140 <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
1141 <li>Any use outside of the loop of an expression derived from the indvar
1142 is changed to compute the derived value outside of the loop, eliminating
1143 the dependence on the exit value of the induction variable. If the only
1144 purpose of the loop is to compute the exit value of some derived
1145 expression, this transformation will make the loop dead.</li>
Gordon Henriksene626bbe2007-11-04 16:17:00 +0000[diff] [blame]1146 </ol>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1147
1148 <p>
1149 This transformation should be followed by strength reduction after all of the
1150 desired loop transformations have been performed. Additionally, on targets
1151 where it is profitable, the loop could be transformed to count down to zero
1152 (the "do loop" optimization).
1153 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1154</div>
1155
1156<!-------------------------------------------------------------------------- -->
1157<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1158 <a name="inline">-inline: Function Integration/Inlining</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1159</div>
1160<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1161 <p>
1162 Bottom-up inlining of functions into callees.
1163 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1164</div>
1165
1166<!-------------------------------------------------------------------------- -->
1167<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1168 <a name="insert-edge-profiling">-insert-edge-profiling: Insert instrumentation for edge profiling</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1169</div>
1170<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1171 <p>
1172 This pass instruments the specified program with counters for edge profiling.
1173 Edge profiling can give a reasonable approximation of the hot paths through a
1174 program, and is used for a wide variety of program transformations.
1175 </p>
1176
1177 <p>
1178 Note that this implementation is very naïve. It inserts a counter for
1179 <em>every</em> edge in the program, instead of using control flow information
1180 to prune the number of counters inserted.
1181 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1182</div>
1183
1184<!-------------------------------------------------------------------------- -->
1185<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1186 <a name="insert-optimal-edge-profiling">-insert-optimal-edge-profiling: Insert optimal instrumentation for edge profiling</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1187</div>
1188<div class="doc_text">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1189 <p>This pass instruments the specified program with counters for edge profiling.
1190 Edge profiling can give a reasonable approximation of the hot paths through a
1191 program, and is used for a wide variety of program transformations.
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1192 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1193</div>
1194
1195<!-------------------------------------------------------------------------- -->
1196<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1197 <a name="instcombine">-instcombine: Combine redundant instructions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1198</div>
1199<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1200 <p>
1201 Combine instructions to form fewer, simple
1202 instructions. This pass does not modify the CFG This pass is where algebraic
1203 simplification happens.
1204 </p>
1205
1206 <p>
1207 This pass combines things like:
1208 </p>
1209
1210<blockquote><pre
1211>%Y = add i32 %X, 1
1212%Z = add i32 %Y, 1</pre></blockquote>
1213
1214 <p>
1215 into:
1216 </p>
1217
1218<blockquote><pre
1219>%Z = add i32 %X, 2</pre></blockquote>
1220
1221 <p>
1222 This is a simple worklist driven algorithm.
1223 </p>
1224
1225 <p>
1226 This pass guarantees that the following canonicalizations are performed on
1227 the program:
1228 </p>
1229
1230 <ul>
1231 <li>If a binary operator has a constant operand, it is moved to the right-
1232 hand side.</li>
1233 <li>Bitwise operators with constant operands are always grouped so that
1234 shifts are performed first, then <code>or</code>s, then
1235 <code>and</code>s, then <code>xor</code>s.</li>
1236 <li>Compare instructions are converted from <code>&lt;</code>,
1237 <code>&gt;</code>, <code>≤</code>, or <code>≥</code> to
1238 <code>=</code> or <code>≠</code> if possible.</li>
1239 <li>All <code>cmp</code> instructions on boolean values are replaced with
1240 logical operations.</li>
1241 <li><code>add <var>X</var>, <var>X</var></code> is represented as
1242 <code>mul <var>X</var>, 2</code> ⇒ <code>shl <var>X</var>, 1</code></li>
1243 <li>Multiplies with a constant power-of-two argument are transformed into
1244 shifts.</li>
1245 <li>… etc.</li>
1246 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1247</div>
1248
1249<!-------------------------------------------------------------------------- -->
1250<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1251 <a name="internalize">-internalize: Internalize Global Symbols</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1252</div>
1253<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1254 <p>
1255 This pass loops over all of the functions in the input module, looking for a
1256 main function. If a main function is found, all other functions and all
1257 global variables with initializers are marked as internal.
1258 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1259</div>
1260
1261<!-------------------------------------------------------------------------- -->
1262<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1263 <a name="ipconstprop">-ipconstprop: Interprocedural constant propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1264</div>
1265<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1266 <p>
1267 This pass implements an <em>extremely</em> simple interprocedural constant
1268 propagation pass. It could certainly be improved in many different ways,
1269 like using a worklist. This pass makes arguments dead, but does not remove
1270 them. The existing dead argument elimination pass should be run after this
1271 to clean up the mess.
1272 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1273</div>
1274
1275<!-------------------------------------------------------------------------- -->
1276<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1277 <a name="ipsccp">-ipsccp: Interprocedural Sparse Conditional Constant Propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1278</div>
1279<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1280 <p>
1281 An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
1282 Propagation</a>.
1283 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1284</div>
1285
1286<!-------------------------------------------------------------------------- -->
1287<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1288 <a name="jump-threading">-jump-threading: Thread control through conditional blocks</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1289</div>
1290<div class="doc_text">
1291 <p>
1292 Jump threading tries to find distinct threads of control flow running through
1293 a basic block. This pass looks at blocks that have multiple predecessors and
1294 multiple successors. If one or more of the predecessors of the block can be
1295 proven to always cause a jump to one of the successors, we forward the edge
1296 from the predecessor to the successor by duplicating the contents of this
1297 block.
1298 </p>
1299 <p>
1300 An example of when this can occur is code like this:
1301 </p>
1302
1303 <pre
1304>if () { ...
1305 X = 4;
1306}
1307if (X &lt; 3) {</pre>
1308
1309 <p>
1310 In this case, the unconditional branch at the end of the first if can be
1311 revectored to the false side of the second if.
1312 </p>
1313</div>
1314
1315<!-------------------------------------------------------------------------- -->
1316<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1317 <a name="lcssa">-lcssa: Loop-Closed SSA Form Pass</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1318</div>
1319<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1320 <p>
1321 This pass transforms loops by placing phi nodes at the end of the loops for
1322 all values that are live across the loop boundary. For example, it turns
1323 the left into the right code:
1324 </p>
1325
1326 <pre
1327>for (...) for (...)
1328 if (c) if (c)
1329 X1 = ... X1 = ...
1330 else else
1331 X2 = ... X2 = ...
1332 X3 = phi(X1, X2) X3 = phi(X1, X2)
1333... = X3 + 4 X4 = phi(X3)
1334 ... = X4 + 4</pre>
1335
1336 <p>
1337 This is still valid LLVM; the extra phi nodes are purely redundant, and will
1338 be trivially eliminated by <code>InstCombine</code>. The major benefit of
1339 this transformation is that it makes many other loop optimizations, such as
1340 LoopUnswitching, simpler.
1341 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1342</div>
1343
1344<!-------------------------------------------------------------------------- -->
1345<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1346 <a name="licm">-licm: Loop Invariant Code Motion</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1347</div>
1348<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1349 <p>
1350 This pass performs loop invariant code motion, attempting to remove as much
1351 code from the body of a loop as possible. It does this by either hoisting
1352 code into the preheader block, or by sinking code to the exit blocks if it is
1353 safe. This pass also promotes must-aliased memory locations in the loop to
1354 live in registers, thus hoisting and sinking "invariant" loads and stores.
1355 </p>
1356
1357 <p>
1358 This pass uses alias analysis for two purposes:
1359 </p>
1360
1361 <ul>
1362 <li>Moving loop invariant loads and calls out of loops. If we can determine
1363 that a load or call inside of a loop never aliases anything stored to,
1364 we can hoist it or sink it like any other instruction.</li>
1365 <li>Scalar Promotion of Memory - If there is a store instruction inside of
1366 the loop, we try to move the store to happen AFTER the loop instead of
1367 inside of the loop. This can only happen if a few conditions are true:
1368 <ul>
1369 <li>The pointer stored through is loop invariant.</li>
1370 <li>There are no stores or loads in the loop which <em>may</em> alias
1371 the pointer. There are no calls in the loop which mod/ref the
1372 pointer.</li>
1373 </ul>
1374 If these conditions are true, we can promote the loads and stores in the
1375 loop of the pointer to use a temporary alloca'd variable. We then use
1376 the mem2reg functionality to construct the appropriate SSA form for the
1377 variable.</li>
1378 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1379</div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1380<!-------------------------------------------------------------------------- -->
1381<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1382 <a name="loop-deletion">-loop-deletion: Dead Loop Deletion Pass</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1383</div>
1384<div class="doc_text">
1385 <p>
1386 This file implements the Dead Loop Deletion Pass. This pass is responsible
1387 for eliminating loops with non-infinite computable trip counts that have no
1388 side effects or volatile instructions, and do not contribute to the
1389 computation of the function's return value.
1390 </p>
1391</div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1392
1393<!-------------------------------------------------------------------------- -->
1394<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1395 <a name="loop-extract">-loop-extract: Extract loops into new functions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1396</div>
1397<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1398 <p>
1399 A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
1400 extract each top-level loop into its own new function. If the loop is the
1401 <em>only</em> loop in a given function, it is not touched. This is a pass most
1402 useful for debugging via bugpoint.
1403 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1404</div>
1405
1406<!-------------------------------------------------------------------------- -->
1407<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1408 <a name="loop-extract-single">-loop-extract-single: Extract at most one loop into a new function</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1409</div>
1410<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1411 <p>
1412 Similar to <a href="#loop-extract">Extract loops into new functions</a>,
1413 this pass extracts one natural loop from the program into a function if it
1414 can. This is used by bugpoint.
1415 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1416</div>
1417
1418<!-------------------------------------------------------------------------- -->
1419<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1420 <a name="loop-index-split">-loop-index-split: Index Split Loops</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1421</div>
1422<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1423 <p>
1424 This pass divides loop's iteration range by spliting loop such that each
1425 individual loop is executed efficiently.
1426 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1427</div>
1428
1429<!-------------------------------------------------------------------------- -->
1430<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1431 <a name="loop-reduce">-loop-reduce: Loop Strength Reduction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1432</div>
1433<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1434 <p>
1435 This pass performs a strength reduction on array references inside loops that
1436 have as one or more of their components the loop induction variable. This is
1437 accomplished by creating a new value to hold the initial value of the array
1438 access for the first iteration, and then creating a new GEP instruction in
1439 the loop to increment the value by the appropriate amount.
1440 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1441</div>
1442
1443<!-------------------------------------------------------------------------- -->
1444<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1445 <a name="loop-rotate">-loop-rotate: Rotate Loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1446</div>
1447<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1448 <p>A simple loop rotation transformation.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1449</div>
1450
1451<!-------------------------------------------------------------------------- -->
1452<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1453 <a name="loop-unroll">-loop-unroll: Unroll loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1454</div>
1455<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1456 <p>
1457 This pass implements a simple loop unroller. It works best when loops have
1458 been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
1459 allowing it to determine the trip counts of loops easily.
1460 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1461</div>
1462
1463<!-------------------------------------------------------------------------- -->
1464<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1465 <a name="loop-unswitch">-loop-unswitch: Unswitch loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1466</div>
1467<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1468 <p>
1469 This pass transforms loops that contain branches on loop-invariant conditions
1470 to have multiple loops. For example, it turns the left into the right code:
1471 </p>
1472
1473 <pre
1474>for (...) if (lic)
1475 A for (...)
1476 if (lic) A; B; C
1477 B else
1478 C for (...)
1479 A; C</pre>
1480
1481 <p>
1482 This can increase the size of the code exponentially (doubling it every time
1483 a loop is unswitched) so we only unswitch if the resultant code will be
1484 smaller than a threshold.
1485 </p>
1486
1487 <p>
1488 This pass expects LICM to be run before it to hoist invariant conditions out
1489 of the loop, to make the unswitching opportunity obvious.
1490 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1491</div>
1492
1493<!-------------------------------------------------------------------------- -->
1494<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1495 <a name="loopsimplify">-loopsimplify: Canonicalize natural loops</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1496</div>
1497<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1498 <p>
1499 This pass performs several transformations to transform natural loops into a
1500 simpler form, which makes subsequent analyses and transformations simpler and
1501 more effective.
1502 </p>
1503
1504 <p>
1505 Loop pre-header insertion guarantees that there is a single, non-critical
1506 entry edge from outside of the loop to the loop header. This simplifies a
1507 number of analyses and transformations, such as LICM.
1508 </p>
1509
1510 <p>
1511 Loop exit-block insertion guarantees that all exit blocks from the loop
1512 (blocks which are outside of the loop that have predecessors inside of the
1513 loop) only have predecessors from inside of the loop (and are thus dominated
1514 by the loop header). This simplifies transformations such as store-sinking
1515 that are built into LICM.
1516 </p>
1517
1518 <p>
1519 This pass also guarantees that loops will have exactly one backedge.
1520 </p>
1521
1522 <p>
1523 Note that the simplifycfg pass will clean up blocks which are split out but
1524 end up being unnecessary, so usage of this pass should not pessimize
1525 generated code.
1526 </p>
1527
1528 <p>
1529 This pass obviously modifies the CFG, but updates loop information and
1530 dominator information.
1531 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1532</div>
1533
1534<!-------------------------------------------------------------------------- -->
1535<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1536 <a name="lowerallocs">-lowerallocs: Lower allocations from instructions to calls</a>
1537</div>
1538<div class="doc_text">
1539 <p>
1540 Turn <tt>malloc</tt> and <tt>free</tt> instructions into <tt>@malloc</tt> and
1541 <tt>@free</tt> calls.
1542 </p>
1543
1544 <p>
1545 This is a target-dependent tranformation because it depends on the size of
1546 data types and alignment constraints.
1547 </p>
1548</div>
1549
1550<!-------------------------------------------------------------------------- -->
1551<div class="doc_subsection">
1552 <a name="lowerinvoke">-lowerinvoke: Lower invoke and unwind, for unwindless code generators</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1553</div>
1554<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1555 <p>
1556 This transformation is designed for use by code generators which do not yet
1557 support stack unwinding. This pass supports two models of exception handling
1558 lowering, the 'cheap' support and the 'expensive' support.
1559 </p>
1560
1561 <p>
1562 'Cheap' exception handling support gives the program the ability to execute
1563 any program which does not "throw an exception", by turning 'invoke'
1564 instructions into calls and by turning 'unwind' instructions into calls to
1565 abort(). If the program does dynamically use the unwind instruction, the
1566 program will print a message then abort.
1567 </p>
1568
1569 <p>
1570 'Expensive' exception handling support gives the full exception handling
1571 support to the program at the cost of making the 'invoke' instruction
1572 really expensive. It basically inserts setjmp/longjmp calls to emulate the
1573 exception handling as necessary.
1574 </p>
1575
1576 <p>
1577 Because the 'expensive' support slows down programs a lot, and EH is only
1578 used for a subset of the programs, it must be specifically enabled by the
1579 <tt>-enable-correct-eh-support</tt> option.
1580 </p>
1581
1582 <p>
1583 Note that after this pass runs the CFG is not entirely accurate (exceptional
1584 control flow edges are not correct anymore) so only very simple things should
1585 be done after the lowerinvoke pass has run (like generation of native code).
1586 This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
1587 support the invoke instruction yet" lowering pass.
1588 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1589</div>
1590
1591<!-------------------------------------------------------------------------- -->
1592<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1593 <a name="lowersetjmp">-lowersetjmp: Lower Set Jump</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1594</div>
1595<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1596 <p>
1597 Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
1598 instructions as necessary.
1599 </p>
1600
1601 <p>
1602 Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
1603 call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
1604 This unwinds the stack for us calling all of the destructors for
1605 objects allocated on the stack.
1606 </p>
1607
1608 <p>
1609 At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
1610 removed. The calls in a function that have a <tt>setjmp</tt> are converted to
1611 invoke where the except part checks to see if it's a <tt>longjmp</tt>
1612 exception and, if so, if it's handled in the function. If it is, then it gets
1613 the value returned by the <tt>longjmp</tt> and goes to where the basic block
1614 was split. <tt>invoke</tt> instructions are handled in a similar fashion with
1615 the original except block being executed if it isn't a <tt>longjmp</tt>
1616 except that is handled by that function.
1617 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1618</div>
1619
1620<!-------------------------------------------------------------------------- -->
1621<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1622 <a name="lowerswitch">-lowerswitch: Lower SwitchInst's to branches</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1623</div>
1624<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1625 <p>
1626 Rewrites <tt>switch</tt> instructions with a sequence of branches, which
1627 allows targets to get away with not implementing the switch instruction until
1628 it is convenient.
1629 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1630</div>
1631
1632<!-------------------------------------------------------------------------- -->
1633<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1634 <a name="mem2reg">-mem2reg: Promote Memory to Register</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1635</div>
1636<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1637 <p>
1638 This file promotes memory references to be register references. It promotes
1639 <tt>alloca</tt> instructions which only have <tt>load</tt>s and
1640 <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
1641 frontiers to place <tt>phi</tt> nodes, then traversing the function in
1642 depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
1643 appropriate. This is just the standard SSA construction algorithm to construct
1644 "pruned" SSA form.
1645 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1646</div>
1647
1648<!-------------------------------------------------------------------------- -->
1649<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1650 <a name="memcpyopt">-memcpyopt: Optimize use of memcpy and friend</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1651</div>
1652<div class="doc_text">
1653 <p>
1654 This pass performs various transformations related to eliminating memcpy
1655 calls, or transforming sets of stores into memset's.
1656 </p>
1657</div>
1658
1659<!-------------------------------------------------------------------------- -->
1660<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1661 <a name="mergefunc">-mergefunc: Merge Functions</a>
1662</div>
1663<div class="doc_text">
1664 <p>This pass looks for equivalent functions that are mergable and folds them.
1665
1666 A hash is computed from the function, based on its type and number of
1667 basic blocks.
1668
1669 Once all hashes are computed, we perform an expensive equality comparison
1670 on each function pair. This takes n^2/2 comparisons per bucket, so it's
1671 important that the hash function be high quality. The equality comparison
1672 iterates through each instruction in each basic block.
1673
1674 When a match is found the functions are folded. If both functions are
1675 overridable, we move the functionality into a new internal function and
1676 leave two overridable thunks to it.
1677 </p>
1678</div>
1679
1680<!-------------------------------------------------------------------------- -->
1681<div class="doc_subsection">
1682 <a name="mergereturn">-mergereturn: Unify function exit nodes</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1683</div>
1684<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1685 <p>
1686 Ensure that functions have at most one <tt>ret</tt> instruction in them.
1687 Additionally, it keeps track of which node is the new exit node of the CFG.
1688 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1689</div>
1690
1691<!-------------------------------------------------------------------------- -->
1692<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1693 <a name="partial-inliner">-partial-inliner: Partial Inliner</a>
1694</div>
1695<div class="doc_text">
1696 <p>This pass performs partial inlining, typically by inlining an if
1697 statement that surrounds the body of the function.
1698 </p>
1699</div>
1700
1701<!-------------------------------------------------------------------------- -->
1702<div class="doc_subsection">
1703 <a name="partialspecialization">-partialspecialization: Partial Specialization</a>
1704</div>
1705<div class="doc_text">
1706 <p>This pass finds function arguments that are often a common constant and
1707 specializes a version of the called function for that constant.
1708
1709 This pass simply does the cloning for functions it specializes. It depends
1710 on <a href="#ipsccp">IPSCCP</a> and <a href="#deadargelim">DAE</a> to clean up the results.
1711
1712 The initial heuristic favors constant arguments that are used in control
1713 flow.
1714 </p>
1715</div>
1716
1717<!-------------------------------------------------------------------------- -->
1718<div class="doc_subsection">
1719 <a name="prune-eh">-prune-eh: Remove unused exception handling info</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1720</div>
1721<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1722 <p>
1723 This file implements a simple interprocedural pass which walks the call-graph,
1724 turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
1725 only if the callee cannot throw an exception. It implements this as a
1726 bottom-up traversal of the call-graph.
1727 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1728</div>
1729
1730<!-------------------------------------------------------------------------- -->
1731<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1732 <a name="reassociate">-reassociate: Reassociate expressions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1733</div>
1734<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1735 <p>
1736 This pass reassociates commutative expressions in an order that is designed
1737 to promote better constant propagation, GCSE, LICM, PRE, etc.
1738 </p>
1739
1740 <p>
1741 For example: 4 + (<var>x</var> + 5) ⇒ <var>x</var> + (4 + 5)
1742 </p>
1743
1744 <p>
1745 In the implementation of this algorithm, constants are assigned rank = 0,
1746 function arguments are rank = 1, and other values are assigned ranks
1747 corresponding to the reverse post order traversal of current function
1748 (starting at 2), which effectively gives values in deep loops higher rank
1749 than values not in loops.
1750 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1751</div>
1752
1753<!-------------------------------------------------------------------------- -->
1754<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1755 <a name="reg2mem">-reg2mem: Demote all values to stack slots</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1756</div>
1757<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1758 <p>
1759 This file demotes all registers to memory references. It is intented to be
1760 the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]1761 <tt>load</tt> instructions, the only values live across basic blocks are
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1762 <tt>alloca</tt> instructions and <tt>load</tt> instructions before
1763 <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
1764 easier. To make later hacking easier, the entry block is split into two, such
1765 that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
1766 entry block.
1767 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1768</div>
1769
1770<!-------------------------------------------------------------------------- -->
1771<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1772 <a name="scalarrepl">-scalarrepl: Scalar Replacement of Aggregates</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1773</div>
1774<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1775 <p>
1776 The well-known scalar replacement of aggregates transformation. This
1777 transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
1778 or array) into individual <tt>alloca</tt> instructions for each member if
1779 possible. Then, if possible, it transforms the individual <tt>alloca</tt>
1780 instructions into nice clean scalar SSA form.
1781 </p>
1782
1783 <p>
1784 This combines a simple scalar replacement of aggregates algorithm with the <a
1785 href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
1786 especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
1787 then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
1788 promote works well.
1789 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1790</div>
1791
1792<!-------------------------------------------------------------------------- -->
1793<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1794 <a name="sccp">-sccp: Sparse Conditional Constant Propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1795</div>
1796<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1797 <p>
1798 Sparse conditional constant propagation and merging, which can be summarized
1799 as:
1800 </p>
1801
1802 <ol>
1803 <li>Assumes values are constant unless proven otherwise</li>
1804 <li>Assumes BasicBlocks are dead unless proven otherwise</li>
1805 <li>Proves values to be constant, and replaces them with constants</li>
1806 <li>Proves conditional branches to be unconditional</li>
1807 </ol>
1808
1809 <p>
1810 Note that this pass has a habit of making definitions be dead. It is a good
1811 idea to to run a DCE pass sometime after running this pass.
1812 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1813</div>
1814
1815<!-------------------------------------------------------------------------- -->
1816<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1817 <a name="sink">-sink: Code Sinking</a>
1818</div>
1819<div class="doc_text">
1820 <p>This pass moves instructions into successor blocks, when possible, so that
1821 they aren't executed on paths where their results aren't needed.
1822 </p>
1823</div>
1824
1825<!-------------------------------------------------------------------------- -->
1826<div class="doc_subsection">
1827 <a name="simplify-libcalls">-simplify-libcalls: Simplify well-known library calls</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1828</div>
1829<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1830 <p>
1831 Applies a variety of small optimizations for calls to specific well-known
1832 function calls (e.g. runtime library functions). For example, a call
1833 <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
1834 transformed into simply <tt>return 3</tt>.
1835 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1836</div>
1837
1838<!-------------------------------------------------------------------------- -->
1839<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1840 <a name="simplify-libcalls-halfpowr">-simplify-libcalls-halfpowr: Simplify half_powr library calls</a>
1841</div>
1842<div class="doc_text">
1843 <p>Simple pass that applies an experimental transformation on calls
1844 to specific functions.
1845 </p>
1846</div>
1847
1848<!-------------------------------------------------------------------------- -->
1849<div class="doc_subsection">
1850 <a name="simplifycfg">-simplifycfg: Simplify the CFG</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1851</div>
1852<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1853 <p>
1854 Performs dead code elimination and basic block merging. Specifically:
1855 </p>
1856
1857 <ol>
1858 <li>Removes basic blocks with no predecessors.</li>
1859 <li>Merges a basic block into its predecessor if there is only one and the
1860 predecessor only has one successor.</li>
1861 <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
1862 <li>Eliminates a basic block that only contains an unconditional
1863 branch.</li>
1864 </ol>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1865</div>
1866
1867<!-------------------------------------------------------------------------- -->
1868<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1869 <a name="split-geps">-split-geps: Split complex GEPs into simple GEPs</a>
1870</div>
1871<div class="doc_text">
1872 <p>This function breaks GEPs with more than 2 non-zero operands into smaller
1873 GEPs each with no more than 2 non-zero operands. This exposes redundancy
1874 between GEPs with common initial operand sequences.
1875 </p>
1876</div>
1877
1878<!-------------------------------------------------------------------------- -->
1879<div class="doc_subsection">
1880 <a name="ssi">-ssi: Static Single Information Construction</a>
1881</div>
1882<div class="doc_text">
1883 <p>This pass converts a list of variables to the Static Single Information
1884 form.
1885
1886 We are building an on-demand representation, that is, we do not convert
1887 every single variable in the target function to SSI form. Rather, we receive
1888 a list of target variables that must be converted. We also do not
1889 completely convert a target variable to the SSI format. Instead, we only
1890 change the variable in the points where new information can be attached
1891 to its live range, that is, at branch points.
1892 </p>
1893</div>
1894
1895<!-------------------------------------------------------------------------- -->
1896<div class="doc_subsection">
1897 <a name="ssi-everything">-ssi-everything: Static Single Information Construction (everything, intended for debugging)</a>
1898</div>
1899<div class="doc_text">
1900 <p>A pass that runs <a href="#ssi">SSI</a> on every non-void variable, intended for debugging.
1901 </p>
1902</div>
1903
1904<!-------------------------------------------------------------------------- -->
1905<div class="doc_subsection">
1906 <a name="strip">-strip: Strip all symbols from a module</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1907</div>
1908<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1909 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1910 performs code stripping. this transformation can delete:
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1911 </p>
1912
1913 <ol>
1914 <li>names for virtual registers</li>
1915 <li>symbols for internal globals and functions</li>
1916 <li>debug information</li>
1917 </ol>
1918
1919 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1920 note that this transformation makes code much less readable, so it should
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1921 only be used in situations where the <tt>strip</tt> utility would be used,
1922 such as reducing code size or making it harder to reverse engineer code.
1923 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1924</div>
1925
1926<!-------------------------------------------------------------------------- -->
1927<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1928 <a name="strip-dead-prototypes">-strip-dead-prototypes: Remove unused function declarations</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1929</div>
1930<div class="doc_text">
1931 <p>
1932 This pass loops over all of the functions in the input module, looking for
1933 dead declarations and removes them. Dead declarations are declarations of
1934 functions for which no implementation is available (i.e., declarations for
1935 unused library functions).
1936 </p>
1937</div>
1938
1939<!-------------------------------------------------------------------------- -->
1940<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1941 <a name="strip-debug-declare">-strip-debug-declare: Strip all llvm.dbg.declare intrinsics</a>
1942</div>
1943<div class="doc_text">
1944 <p>This pass implements code stripping. Specifically, it can delete:
1945 <ul>
1946 <li>names for virtual registers</li>
1947 <li>symbols for internal globals and functions</li>
1948 <li>debug information</li>
1949 </ul>
1950 Note that this transformation makes code much less readable, so it should
1951 only be used in situations where the 'strip' utility would be used, such as
1952 reducing code size or making it harder to reverse engineer code.
1953 </p>
1954</div>
1955
1956<!-------------------------------------------------------------------------- -->
1957<div class="doc_subsection">
1958 <a name="strip-nondebug">-strip-nondebug: Strip all symbols, except dbg symbols, from a module</a>
1959</div>
1960<div class="doc_text">
1961 <p>This pass implements code stripping. Specifically, it can delete:
1962 <ul>
1963 <li>names for virtual registers</li>
1964 <li>symbols for internal globals and functions</li>
1965 <li>debug information</li>
1966 </ul>
1967 Note that this transformation makes code much less readable, so it should
1968 only be used in situations where the 'strip' utility would be used, such as
1969 reducing code size or making it harder to reverse engineer code.
1970 </p>
1971</div>
1972
1973<!-------------------------------------------------------------------------- -->
1974<div class="doc_subsection">
1975 <a name="sretpromotion">-sretpromotion: Promote sret arguments</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1976</div>
1977<div class="doc_text">
1978 <p>
1979 This pass finds functions that return a struct (using a pointer to the struct
1980 as the first argument of the function, marked with the '<tt>sret</tt>' attribute) and
1981 replaces them with a new function that simply returns each of the elements of
1982 that struct (using multiple return values).
1983 </p>
1984
1985 <p>
1986 This pass works under a number of conditions:
1987 </p>
1988
1989 <ul>
1990 <li>The returned struct must not contain other structs</li>
1991 <li>The returned struct must only be used to load values from</li>
1992 <li>The placeholder struct passed in is the result of an <tt>alloca</tt></li>
1993 </ul>
1994</div>
1995
1996<!-------------------------------------------------------------------------- -->
1997<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1998 <a name="tailcallelim">-tailcallelim: Tail Call Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1999</div>
2000<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]2001 <p>
2002 This file transforms calls of the current function (self recursion) followed
2003 by a return instruction with a branch to the entry of the function, creating
2004 a loop. This pass also implements the following extensions to the basic
2005 algorithm:
2006 </p>
2007
2008 <ul>
2009 <li>Trivial instructions between the call and return do not prevent the
2010 transformation from taking place, though currently the analysis cannot
2011 support moving any really useful instructions (only dead ones).
2012 <li>This pass transforms functions that are prevented from being tail
2013 recursive by an associative expression to use an accumulator variable,
2014 thus compiling the typical naive factorial or <tt>fib</tt> implementation
2015 into efficient code.
2016 <li>TRE is performed if the function returns void, if the return
2017 returns the result returned by the call, or if the function returns a
2018 run-time constant on all exits from the function. It is possible, though
2019 unlikely, that the return returns something else (like constant 0), and
2020 can still be TRE'd. It can be TRE'd if <em>all other</em> return
2021 instructions in the function return the exact same value.
2022 <li>If it can prove that callees do not access theier caller stack frame,
2023 they are marked as eligible for tail call elimination (by the code
2024 generator).
2025 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2026</div>
2027
2028<!-------------------------------------------------------------------------- -->
2029<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2030 <a name="tailduplicate">-tailduplicate: Tail Duplication</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2031</div>
2032<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]2033 <p>
2034 This pass performs a limited form of tail duplication, intended to simplify
2035 CFGs by removing some unconditional branches. This pass is necessary to
2036 straighten out loops created by the C front-end, but also is capable of
2037 making other code nicer. After this pass is run, the CFG simplify pass
2038 should be run to clean up the mess.
2039 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2040</div>
2041
2042<!-- ======================================================================= -->
2043<div class="doc_section"> <a name="transform">Utility Passes</a></div>
2044<div class="doc_text">
2045 <p>This section describes the LLVM Utility Passes.</p>
2046</div>
2047
2048<!-------------------------------------------------------------------------- -->
2049<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2050 <a name="deadarghaX0r">-deadarghaX0r: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2051</div>
2052<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2053 <p>
2054 Same as dead argument elimination, but deletes arguments to functions which
2055 are external. This is only for use by <a
2056 href="Bugpoint.html">bugpoint</a>.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2057</div>
2058
2059<!-------------------------------------------------------------------------- -->
2060<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2061 <a name="extract-blocks">-extract-blocks: Extract Basic Blocks From Module (for bugpoint use)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2062</div>
2063<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2064 <p>
2065 This pass is used by bugpoint to extract all blocks from the module into their
2066 own functions.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2067</div>
2068
2069<!-------------------------------------------------------------------------- -->
2070<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2071 <a name="instnamer">-instnamer: Assign names to anonymous instructions</a>
2072</div>
2073<div class="doc_text">
2074 <p>This is a little utility pass that gives instructions names, this is mostly
2075 useful when diffing the effect of an optimization because deleting an
2076 unnamed instruction can change all other instruction numbering, making the
2077 diff very noisy.
2078 </p>
2079</div>
2080
2081<!-------------------------------------------------------------------------- -->
2082<div class="doc_subsection">
2083 <a name="preverify">-preverify: Preliminary module verification</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2084</div>
2085<div class="doc_text">
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]2086 <p>
2087 Ensures that the module is in the form required by the <a
2088 href="#verifier">Module Verifier</a> pass.
2089 </p>
2090
2091 <p>
2092 Running the verifier runs this pass automatically, so there should be no need
2093 to use it directly.
2094 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2095</div>
2096
2097<!-------------------------------------------------------------------------- -->
2098<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2099 <a name="verify">-verify: Module Verifier</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2100</div>
2101<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2102 <p>
2103 Verifies an LLVM IR code. This is useful to run after an optimization which is
2104 undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
2105 emitting bitcode, and also that malformed bitcode is likely to make LLVM
2106 crash. All language front-ends are therefore encouraged to verify their output
2107 before performing optimizing transformations.
2108 </p>
2109
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]2110 <ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2111 <li>Both of a binary operator's parameters are of the same type.</li>
2112 <li>Verify that the indices of mem access instructions match other
2113 operands.</li>
2114 <li>Verify that arithmetic and other things are only performed on
2115 first-class types. Verify that shifts and logicals only happen on
2116 integrals f.e.</li>
2117 <li>All of the constants in a switch statement are of the correct type.</li>
2118 <li>The code is in valid SSA form.</li>
Chris Lattner46b3abc2009-10-28 04:47:06 +0000[diff] [blame]2119 <li>It is illegal to put a label into any other type (like a structure) or
2120 to return one.</li>
Nick Lewycky0c78ac12008-03-28 06:46:51 +0000[diff] [blame]2121 <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]2122 invalid.</li>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2123 <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
2124 <li>PHI nodes must be the first thing in a basic block, all grouped
2125 together.</li>
2126 <li>PHI nodes must have at least one entry.</li>
2127 <li>All basic blocks should only end with terminator insts, not contain
2128 them.</li>
2129 <li>The entry node to a function must not have predecessors.</li>
2130 <li>All Instructions must be embedded into a basic block.</li>
2131 <li>Functions cannot take a void-typed parameter.</li>
2132 <li>Verify that a function's argument list agrees with its declared
2133 type.</li>
2134 <li>It is illegal to specify a name for a void value.</li>
2135 <li>It is illegal to have a internal global value with no initializer.</li>
2136 <li>It is illegal to have a ret instruction that returns a value that does
2137 not agree with the function return value type.</li>
2138 <li>Function call argument types match the function prototype.</li>
2139 <li>All other things that are tested by asserts spread about the code.</li>
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]2140 </ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2141
2142 <p>
2143 Note that this does not provide full security verification (like Java), but
2144 instead just tries to ensure that code is well-formed.
2145 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2146</div>
2147
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2148<!-------------------------------------------------------------------------- -->
2149<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2150 <a name="view-cfg">-view-cfg: View CFG of function</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2151</div>
2152<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2153 <p>
2154 Displays the control flow graph using the GraphViz tool.
2155 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2156</div>
2157
2158<!-------------------------------------------------------------------------- -->
2159<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2160 <a name="view-cfg-only">-view-cfg-only: View CFG of function (with no function bodies)</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2161</div>
2162<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2163 <p>
2164 Displays the control flow graph using the GraphViz tool, but omitting function
2165 bodies.
2166 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2167</div>
2168
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2169<!-------------------------------------------------------------------------- -->
2170<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2171 <a name="view-dom">-view-dom: View dominator tree of function</a>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2172</div>
2173<div class="doc_text">
2174 <p>
2175 Displays the dominator tree using the GraphViz tool.
2176 </p>
2177</div>
2178
2179<!-------------------------------------------------------------------------- -->
2180<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2181 <a name="view-dom-only">-view-dom-only: View dominator tree of function (with no function
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2182 bodies)
2183 </a>
2184</div>
2185<div class="doc_text">
2186 <p>
2187 Displays the dominator tree using the GraphViz tool, but omitting function
2188 bodies.
2189 </p>
2190</div>
2191
2192<!-------------------------------------------------------------------------- -->
2193<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2194 <a name="view-postdom">-view-postdom: View post dominator tree of function</a>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2195</div>
2196<div class="doc_text">
2197 <p>
2198 Displays the post dominator tree using the GraphViz tool.
2199 </p>
2200</div>
2201
2202<!-------------------------------------------------------------------------- -->
2203<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2204 <a name="view-postdom-only">-view-postdom-only: View post dominator tree of function (with no
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2205 function bodies)
2206 </a>
2207</div>
2208<div class="doc_text">
2209 <p>
2210 Displays the post dominator tree using the GraphViz tool, but omitting
2211 function bodies.
2212 </p>
2213</div>
2214
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2215<!-- *********************************************************************** -->
2216
2217<hr>
2218<address>
2219 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]2220 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2221 <a href="http://validator.w3.org/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]2222 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]2223
2224 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
2225 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
2226 Last modified: $Date$
2227</address>
2228
2229</body>
2230</html>