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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 948d9a5b1f2a34b941fcd0c69099b4362ff1a336 / . / docs / Passes.html
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Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksenbd412212007-10-25 08:58:56 +0000[diff] [blame]7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]8</head>
9<body>
10
Gordon Henriksen9c2c7032007-10-25 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 Henriksenbd412212007-10-25 08:58:56 +0000[diff] [blame]24open HELP, "../Release/bin/opt -help|" or die "open: opt -help: $!\n";
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]25while (<HELP>) {
26 m:^ -([^ ]+) +- (.*)$: 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>$2</td></tr>\n";
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]30 push @y, "$o <a name=\"$1\">-$1: $2</a>\n";
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]31}
32@x = map { s/^\d\d\d//; $_ } sort @x;
33@y = map { s/^\d\d\d//; $_ } sort @y;
34print @x, @y;
35EOT
36
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]37This (real) one-liner can also be helpful when converting comments to HTML:
38
39perl -e '$/ = 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 Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]41 -->
42
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]53 <p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
54 and Gordon Henriksen</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]63 The table below divides the passes that LLVM provides into three categories.
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]67 Utility passes provides some utility but don't otherwise fit categorization.
Dan Gohmanf17a25c2007-07-18 16:29:46 +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.
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 Henriksenbd412212007-10-25 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]77<tr><td><a href="#aa-eval">-aa-eval</a></td><td>Exhaustive Alias Analysis Precision Evaluator</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]80<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]84<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
Duncan Sandsd10d6f72008-09-23 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 Grosserc9700032010-05-07 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]92<tr><td><a href="#globalsmodref-aa">-globalsmodref-aa</a></td><td>Simple mod/ref analysis for globals</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]93<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
Duncan Sandsf90c5442010-07-06 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]96<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
Duncan Sandsf90c5442010-07-06 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 Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]104<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
Duncan Sandsf90c5442010-07-06 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]108<tr><td><a href="#pointertracking">-pointertracking</a></td><td>Track pointer bounds</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]109<tr><td><a href="#postdomfrontier">-postdomfrontier</a></td><td>Post-Dominance Frontier Construction</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]110<tr><td><a href="#postdomtree">-postdomtree</a></td><td>Post-Dominator Tree Construction</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]111<tr><td><a href="#print-alias-sets">-print-alias-sets</a></td><td>Alias Set Printer</td></tr>
Duncan Sandsd10d6f72008-09-23 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 Sandsf90c5442010-07-06 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 Sandsd10d6f72008-09-23 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 Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]121<tr><td><a href="#profile-estimator">-profile-estimator</a></td><td>Estimate profiling information</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]122<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
Tobias Grosser11e122f2010-07-22 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 Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]124<tr><td><a href="#profile-verifier">-profile-verifier</a></td><td>Verify profiling information</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]125<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]126<tr><td><a href="#scev-aa">-scev-aa</a></td><td>ScalarEvolution-based Alias Analysis</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]127<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
128
129
Gordon Henriksenbd412212007-10-25 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 Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]132<tr><td><a href="#abcd">-abcd</a></td><td>Remove redundant conditional branches</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]133<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
Duncan Sandsf90c5442010-07-06 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen9c2c7032007-10-25 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 Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]138<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Prepare a function for code generation </td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]146<tr><td><a href="#functionattrs">-functionattrs</a></td><td>Deduce function attributes</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]149<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Sandsf90c5442010-07-06 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen08556692008-05-08 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]161<tr><td><a href="#loop-deletion">-loop-deletion</a></td><td>Dead Loop Deletion Pass </td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +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 Henriksen9c2c7032007-10-25 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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]165<tr><td><a href="#loop-reduce">-loop-reduce</a></td><td>Loop Strength Reduction</td></tr>
Gordon Henriksen9c2c7032007-10-25 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>
Peter Collingbourne948d9a52010-08-03 16:19:16 +0000[diff] [blame^]170<tr><td><a href="#loweratomic">-loweratomic</a></td><td>Lower atomic intrinsics</td></tr>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]171<tr><td><a href="#lowerinvoke">-lowerinvoke</a></td><td>Lower invoke and unwind, for unwindless code generators</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]172<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
173<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
174<tr><td><a href="#mem2reg">-mem2reg</a></td><td>Promote Memory to Register</td></tr>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]175<tr><td><a href="#memcpyopt">-memcpyopt</a></td><td>Optimize use of memcpy and friends</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]176<tr><td><a href="#mergefunc">-mergefunc</a></td><td>Merge Functions</td></tr>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]177<tr><td><a href="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]178<tr><td><a href="#partial-inliner">-partial-inliner</a></td><td>Partial Inliner</td></tr>
179<tr><td><a href="#partialspecialization">-partialspecialization</a></td><td>Partial Specialization</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]180<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]181<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
182<tr><td><a href="#reg2mem">-reg2mem</a></td><td>Demote all values to stack slots</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]183<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates</td></tr>
184<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]185<tr><td><a href="#sink">-sink</a></td><td>Code Sinking</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]186<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]187<tr><td><a href="#simplify-libcalls-halfpowr">-simplify-libcalls-halfpowr</a></td><td>Simplify half_powr library calls</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]188<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]189<tr><td><a href="#split-geps">-split-geps</a></td><td>Split complex GEPs into simple GEPs</td></tr>
190<tr><td><a href="#ssi">-ssi</a></td><td>Static Single Information Construction</td></tr>
191<tr><td><a href="#ssi-everything">-ssi-everything</a></td><td>Static Single Information Construction (everything, intended for debugging)</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]192<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]193<tr><td><a href="#strip-dead-debug-info">-strip-dead-debug-info</a></td><td>Strip debug info for unused symbols</td></tr>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]194<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Remove unused function declarations</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]195<tr><td><a href="#strip-debug-declare">-strip-debug-declare</a></td><td>Strip all llvm.dbg.declare intrinsics</td></tr>
196<tr><td><a href="#strip-nondebug">-strip-nondebug</a></td><td>Strip all symbols, except dbg symbols, from a module</td></tr>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]197<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]198<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
199<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]200
201
Gordon Henriksenbd412212007-10-25 08:58:56 +0000[diff] [blame]202<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
203<tr><th>Option</th><th>Name</th></tr>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]204<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
205<tr><td><a href="#extract-blocks">-extract-blocks</a></td><td>Extract Basic Blocks From Module (for bugpoint use)</td></tr>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]206<tr><td><a href="#instnamer">-instnamer</a></td><td>Assign names to anonymous instructions</td></tr>
Gordon Henriksene88510a2007-11-05 02:05:35 +0000[diff] [blame]207<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]208<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]209<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
210<tr><td><a href="#view-cfg-only">-view-cfg-only</a></td><td>View CFG of function (with no function bodies)</td></tr>
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]211<tr><td><a href="#view-dom">-view-dom</a></td><td>View dominator tree of function</td></tr>
212<tr><td><a href="#view-dom-only">-view-dom-only</a></td><td>View dominator tree of function (with no function bodies)</td></tr>
213<tr><td><a href="#view-postdom">-view-postdom</a></td><td>View post dominator tree of function</td></tr>
214<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>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]215</table>
216</div>
217
218<!-- ======================================================================= -->
219<div class="doc_section"> <a name="example">Analysis Passes</a></div>
220<div class="doc_text">
221 <p>This section describes the LLVM Analysis Passes.</p>
222</div>
223
224<!-------------------------------------------------------------------------- -->
225<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]226 <a name="aa-eval">-aa-eval: Exhaustive Alias Analysis Precision Evaluator</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]227</div>
228<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]229 <p>This is a simple N^2 alias analysis accuracy evaluator.
230 Basically, for each function in the program, it simply queries to see how the
231 alias analysis implementation answers alias queries between each pair of
232 pointers in the function.</p>
233
234 <p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
235 Spadini, and Wojciech Stryjewski.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]236</div>
237
238<!-------------------------------------------------------------------------- -->
239<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]240 <a name="basicaa">-basicaa: Basic Alias Analysis (default AA impl)</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]241</div>
242<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]243 <p>
244 This is the default implementation of the Alias Analysis interface
245 that simply implements a few identities (two different globals cannot alias,
246 etc), but otherwise does no analysis.
247 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]248</div>
249
250<!-------------------------------------------------------------------------- -->
251<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]252 <a name="basiccg">-basiccg: Basic CallGraph Construction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]253</div>
254<div class="doc_text">
255 <p>Yet to be written.</p>
256</div>
257
258<!-------------------------------------------------------------------------- -->
259<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]260 <a name="codegenprepare">-codegenprepare: Optimize for code generation</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]261</div>
262<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]263 <p>
264 This pass munges the code in the input function to better prepare it for
265 SelectionDAG-based code generation. This works around limitations in it's
266 basic-block-at-a-time approach. It should eventually be removed.
267 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]268</div>
269
270<!-------------------------------------------------------------------------- -->
271<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]272 <a name="count-aa">-count-aa: Count Alias Analysis Query Responses</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]273</div>
274<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]275 <p>
276 A pass which can be used to count how many alias queries
277 are being made and how the alias analysis implementation being used responds.
278 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]279</div>
280
281<!-------------------------------------------------------------------------- -->
282<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]283 <a name="debug-aa">-debug-aa: AA use debugger</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]284</div>
285<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]286 <p>
287 This simple pass checks alias analysis users to ensure that if they
288 create a new value, they do not query AA without informing it of the value.
289 It acts as a shim over any other AA pass you want.
290 </p>
291
292 <p>
293 Yes keeping track of every value in the program is expensive, but this is
294 a debugging pass.
295 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]296</div>
297
298<!-------------------------------------------------------------------------- -->
299<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]300 <a name="domfrontier">-domfrontier: Dominance Frontier Construction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]301</div>
302<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]303 <p>
304 This pass is a simple dominator construction algorithm for finding forward
305 dominator frontiers.
306 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]307</div>
308
309<!-------------------------------------------------------------------------- -->
310<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]311 <a name="domtree">-domtree: Dominator Tree Construction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]312</div>
313<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]314 <p>
315 This pass is a simple dominator construction algorithm for finding forward
316 dominators.
317 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]318</div>
319
320<!-------------------------------------------------------------------------- -->
321<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]322 <a name="dot-callgraph">-dot-callgraph: Print Call Graph to 'dot' file</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]323</div>
324<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]325 <p>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]326 This pass, only available in <code>opt</code>, prints the call graph into a
327 <code>.dot</code> graph. This graph can then be processed with the "dot" tool
328 to convert it to postscript or some other suitable format.
329 </p>
330</div>
331
332<!-------------------------------------------------------------------------- -->
333<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]334 <a name="dot-cfg">-dot-cfg: Print CFG of function to 'dot' file</a>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]335</div>
336<div class="doc_text">
337 <p>
338 This pass, only available in <code>opt</code>, prints the control flow graph
339 into a <code>.dot</code> graph. This graph can then be processed with the
340 "dot" tool to convert it to postscript or some other suitable format.
341 </p>
342</div>
343
344<!-------------------------------------------------------------------------- -->
345<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]346 <a name="dot-cfg-only">-dot-cfg-only: Print CFG of function to 'dot' file (with no function bodies)</a>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]347</div>
348<div class="doc_text">
349 <p>
350 This pass, only available in <code>opt</code>, prints the control flow graph
351 into a <code>.dot</code> graph, omitting the function bodies. This graph can
352 then be processed with the "dot" tool to convert it to postscript or some
353 other suitable format.
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]354 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]355</div>
356
357<!-------------------------------------------------------------------------- -->
358<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]359 <a name="dot-dom">-dot-dom: Print dominator tree of function to 'dot' file</a>
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]360</div>
361<div class="doc_text">
362 <p>
363 This pass, only available in <code>opt</code>, prints the dominator tree
364 into a <code>.dot</code> graph. This graph can then be processed with the
365 "dot" tool to convert it to postscript or some other suitable format.
366 </p>
367</div>
368
369<!-------------------------------------------------------------------------- -->
370<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]371 <a name="dot-dom-only">-dot-dom-only: Print dominator tree of function to 'dot' file (with no
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]372 function bodies)</a>
373</div>
374<div class="doc_text">
375 <p>
376 This pass, only available in <code>opt</code>, prints the dominator tree
377 into a <code>.dot</code> graph, omitting the function bodies. This graph can
378 then be processed with the "dot" tool to convert it to postscript or some
379 other suitable format.
380 </p>
381</div>
382
383<!-------------------------------------------------------------------------- -->
384<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]385 <a name="dot-postdom">dot-postdom: Print post dominator tree of function to 'dot' file</a>
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]386</div>
387<div class="doc_text">
388 <p>
389 This pass, only available in <code>opt</code>, prints the post dominator tree
390 into a <code>.dot</code> graph. This graph can then be processed with the
391 "dot" tool to convert it to postscript or some other suitable format.
392 </p>
393</div>
394
395<!-------------------------------------------------------------------------- -->
396<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]397 <a name="dot-postdom-only">dot-postdom-only: Print post dominator tree of function to 'dot' file
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]398 (with no function bodies)</a>
399</div>
400<div class="doc_text">
401 <p>
402 This pass, only available in <code>opt</code>, prints the post dominator tree
403 into a <code>.dot</code> graph, omitting the function bodies. This graph can
404 then be processed with the "dot" tool to convert it to postscript or some
405 other suitable format.
406 </p>
407</div>
408
409<!-------------------------------------------------------------------------- -->
410<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]411 <a name="globalsmodref-aa">-globalsmodref-aa: Simple mod/ref analysis for globals</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]412</div>
413<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]414 <p>
415 This simple pass provides alias and mod/ref information for global values
416 that do not have their address taken, and keeps track of whether functions
417 read or write memory (are "pure"). For this simple (but very common) case,
418 we can provide pretty accurate and useful information.
419 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]420</div>
421
422<!-------------------------------------------------------------------------- -->
423<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]424 <a name="instcount">-instcount: Counts the various types of Instructions</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]425</div>
426<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]427 <p>
428 This pass collects the count of all instructions and reports them
429 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]430</div>
431
432<!-------------------------------------------------------------------------- -->
433<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]434 <a name="interprocedural-aa-eval">-interprocedural-aa-eval: Exhaustive Interprocedural Alias Analysis Precision Evaluator</a>
435</div>
436<div class="doc_text">
437 <p>This pass implements a simple N^2 alias analysis accuracy evaluator.
438 Basically, for each function in the program, it simply queries to see how the
439 alias analysis implementation answers alias queries between each pair of
440 pointers in the function.
441 </p>
442</div>
443
444<!-------------------------------------------------------------------------- -->
445<div class="doc_subsection">
446 <a name="interprocedural-basic-aa">-interprocedural-basic-aa: Interprocedural Basic Alias Analysis</a>
447</div>
448<div class="doc_text">
449 <p>This pass defines the default implementation of the Alias Analysis interface
450 that simply implements a few identities (two different globals cannot alias,
451 etc), but otherwise does no analysis.
452 </p>
453</div>
454
455<!-------------------------------------------------------------------------- -->
456<div class="doc_subsection">
457 <a name="intervals">-intervals: Interval Partition Construction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]458</div>
459<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]460 <p>
461 This analysis calculates and represents the interval partition of a function,
462 or a preexisting interval partition.
463 </p>
464
465 <p>
466 In this way, the interval partition may be used to reduce a flow graph down
467 to its degenerate single node interval partition (unless it is irreducible).
468 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]469</div>
470
471<!-------------------------------------------------------------------------- -->
472<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]473 <a name="iv-users">-iv-users: Induction Variable Users</a>
474</div>
475<div class="doc_text">
476 <p>Bookkeeping for "interesting" users of expressions computed from
477 induction variables.</p>
478</div>
479
480<!-------------------------------------------------------------------------- -->
481<div class="doc_subsection">
482 <a name="lazy-value-info">-lazy-value-info: Lazy Value Information Analysis</a>
483</div>
484<div class="doc_text">
485 <p>Interface for lazy computation of value constraint information.</p>
486</div>
487
488<!-------------------------------------------------------------------------- -->
489<div class="doc_subsection">
490 <a name="lda">-lda: Loop Dependence Analysis</a>
491</div>
492<div class="doc_text">
493 <p>Loop dependence analysis framework, which is used to detect dependences in
494 memory accesses in loops.</p>
495</div>
496
497<!-------------------------------------------------------------------------- -->
498<div class="doc_subsection">
499 <a name="libcall-aa">-libcall-aa: LibCall Alias Analysis</a>
500</div>
501<div class="doc_text">
502 <p>LibCall Alias Analysis.</p>
503</div>
504
505<!-------------------------------------------------------------------------- -->
506<div class="doc_subsection">
507 <a name="lint">-lint: Check for common errors in LLVM IR</a>
508</div>
509<div class="doc_text">
510 <p>This pass statically checks for common and easily-identified constructs
511 which produce undefined or likely unintended behavior in LLVM IR.</p>
512
513 <p>It is not a guarantee of correctness, in two ways. First, it isn't
514 comprehensive. There are checks which could be done statically which are
515 not yet implemented. Some of these are indicated by TODO comments, but
516 those aren't comprehensive either. Second, many conditions cannot be
517 checked statically. This pass does no dynamic instrumentation, so it
518 can't check for all possible problems.</p>
519
520 <p>Another limitation is that it assumes all code will be executed. A store
521 through a null pointer in a basic block which is never reached is harmless,
522 but this pass will warn about it anyway.</p>
523
524 <p>Optimization passes may make conditions that this pass checks for more or
525 less obvious. If an optimization pass appears to be introducing a warning,
526 it may be that the optimization pass is merely exposing an existing
527 condition in the code.</p>
528
529 <p>This code may be run before instcombine. In many cases, instcombine checks
530 for the same kinds of things and turns instructions with undefined behavior
531 into unreachable (or equivalent). Because of this, this pass makes some
532 effort to look through bitcasts and so on.
533 </p>
534</div>
535
536<!-------------------------------------------------------------------------- -->
537<div class="doc_subsection">
538 <a name="live-values">-live-values: Values Liveness Analysis</a>
539</div>
540<div class="doc_text">
541 <p>LLVM IR Value liveness analysis pass.</p>
542</div>
543
544<!-------------------------------------------------------------------------- -->
545<div class="doc_subsection">
546 <a name="loops">-loops: Natural Loop Construction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]547</div>
548<div class="doc_text">
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]549 <p>
550 This analysis is used to identify natural loops and determine the loop depth
551 of various nodes of the CFG. Note that the loops identified may actually be
552 several natural loops that share the same header node... not just a single
553 natural loop.
554 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]555</div>
556
557<!-------------------------------------------------------------------------- -->
558<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]559 <a name="memdep">-memdep: Memory Dependence Analysis</a>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]560</div>
561<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]562 <p>
563 An analysis that determines, for a given memory operation, what preceding
564 memory operations it depends on. It builds on alias analysis information, and
565 tries to provide a lazy, caching interface to a common kind of alias
566 information query.
567 </p>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]568</div>
569
570<!-------------------------------------------------------------------------- -->
571<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]572 <a name="module-debuginfo">-module-debuginfo: Prints module debug info metadata</a>
573</div>
574<div class="doc_text">
575 <p>This pass decodes the debug info metadata in a module and prints in a
576 (sufficiently-prepared-) human-readable form.
577
578 For example, run this pass from opt along with the -analyze option, and
579 it'll print to standard output.
580 </p>
581</div>
582
583<!-------------------------------------------------------------------------- -->
584<div class="doc_subsection">
585 <a name="no-aa">-no-aa: No Alias Analysis (always returns 'may' alias)</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]586</div>
587<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]588 <p>
589 Always returns "I don't know" for alias queries. NoAA is unlike other alias
590 analysis implementations, in that it does not chain to a previous analysis. As
591 such it doesn't follow many of the rules that other alias analyses must.
592 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]593</div>
594
595<!-------------------------------------------------------------------------- -->
596<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]597 <a name="no-profile">-no-profile: No Profile Information</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]598</div>
599<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]600 <p>
601 The default "no profile" implementation of the abstract
602 <code>ProfileInfo</code> interface.
603 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]604</div>
605
606<!-------------------------------------------------------------------------- -->
607<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]608 <a name="pointertracking">-pointertracking: Track pointer bounds.</a>
609</div>
610<div class="doc_text">
611 <p>Tracking of pointer bounds.
612 </p>
613</div>
614
615<!-------------------------------------------------------------------------- -->
616<div class="doc_subsection">
617 <a name="postdomfrontier">-postdomfrontier: Post-Dominance Frontier Construction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]618</div>
619<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]620 <p>
621 This pass is a simple post-dominator construction algorithm for finding
622 post-dominator frontiers.
623 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]624</div>
625
626<!-------------------------------------------------------------------------- -->
627<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]628 <a name="postdomtree">-postdomtree: Post-Dominator Tree Construction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]629</div>
630<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]631 <p>
632 This pass is a simple post-dominator construction algorithm for finding
633 post-dominators.
634 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]635</div>
636
637<!-------------------------------------------------------------------------- -->
638<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]639 <a name="print-alias-sets">-print-alias-sets: Alias Set Printer</a>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]640</div>
641<div class="doc_text">
642 <p>Yet to be written.</p>
643</div>
644
645<!-------------------------------------------------------------------------- -->
646<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]647 <a name="print-callgraph">-print-callgraph: Print a call graph</a>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]648</div>
649<div class="doc_text">
650 <p>
651 This pass, only available in <code>opt</code>, prints the call graph to
652 standard output in a human-readable form.
653 </p>
654</div>
655
656<!-------------------------------------------------------------------------- -->
657<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]658 <a name="print-callgraph-sccs">-print-callgraph-sccs: Print SCCs of the Call Graph</a>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]659</div>
660<div class="doc_text">
661 <p>
662 This pass, only available in <code>opt</code>, prints the SCCs of the call
663 graph to standard output in a human-readable form.
664 </p>
665</div>
666
667<!-------------------------------------------------------------------------- -->
668<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]669 <a name="print-cfg-sccs">-print-cfg-sccs: Print SCCs of each function CFG</a>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]670</div>
671<div class="doc_text">
672 <p>
673 This pass, only available in <code>opt</code>, prints the SCCs of each
674 function CFG to standard output in a human-readable form.
675 </p>
676</div>
677
678<!-------------------------------------------------------------------------- -->
679<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]680 <a name="print-dbginfo">-print-dbginfo: Print debug info in human readable form</a>
681</div>
682<div class="doc_text">
683 <p>Pass that prints instructions, and associated debug info:
684 <ul>
685
686 <li>source/line/col information</li>
687 <li>original variable name</li>
688 <li>original type name</li>
689 </ul>
690
691 </p>
692</div>
693
694<!-------------------------------------------------------------------------- -->
695<div class="doc_subsection">
696 <a name="print-dom-info">-print-dom-info: Dominator Info Printer</a>
697</div>
698<div class="doc_text">
699 <p>Dominator Info Printer.</p>
700</div>
701
702<!-------------------------------------------------------------------------- -->
703<div class="doc_subsection">
704 <a name="print-externalfnconstants">-print-externalfnconstants: Print external fn callsites passed constants</a>
Duncan Sandsd10d6f72008-09-23 12:47:39 +0000[diff] [blame]705</div>
706<div class="doc_text">
707 <p>
708 This pass, only available in <code>opt</code>, prints out call sites to
709 external functions that are called with constant arguments. This can be
710 useful when looking for standard library functions we should constant fold
711 or handle in alias analyses.
712 </p>
713</div>
714
715<!-------------------------------------------------------------------------- -->
716<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]717 <a name="print-function">-print-function: Print function to stderr</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]718</div>
719<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]720 <p>
721 The <code>PrintFunctionPass</code> class is designed to be pipelined with
722 other <code>FunctionPass</code>es, and prints out the functions of the module
723 as they are processed.
724 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]725</div>
726
727<!-------------------------------------------------------------------------- -->
728<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]729 <a name="print-module">-print-module: Print module to stderr</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]730</div>
731<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]732 <p>
733 This pass simply prints out the entire module when it is executed.
734 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]735</div>
736
737<!-------------------------------------------------------------------------- -->
738<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]739 <a name="print-used-types">-print-used-types: Find Used Types</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]740</div>
741<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]742 <p>
743 This pass is used to seek out all of the types in use by the program. Note
744 that this analysis explicitly does not include types only used by the symbol
745 table.
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]746</div>
747
748<!-------------------------------------------------------------------------- -->
749<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]750 <a name="profile-estimator">-profile-estimator: Estimate profiling information</a>
751</div>
752<div class="doc_text">
753 <p>Profiling information that estimates the profiling information
754 in a very crude and unimaginative way.
755 </p>
756</div>
757
758<!-------------------------------------------------------------------------- -->
759<div class="doc_subsection">
760 <a name="profile-loader">-profile-loader: Load profile information from llvmprof.out</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]761</div>
762<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]763 <p>
764 A concrete implementation of profiling information that loads the information
765 from a profile dump file.
766 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]767</div>
768
769<!-------------------------------------------------------------------------- -->
770<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]771 <a name="profile-verifier">-profile-verifier: Verify profiling information</a>
772</div>
773<div class="doc_text">
774 <p>Pass that checks profiling information for plausibility.</p>
775</div>
Tobias Grosser11e122f2010-07-22 07:46:31 +0000[diff] [blame]776<div class="doc_subsection">
777 <a name="regions">-regions: Detect single entry single exit regions in a function</a>
778</div>
779<div class="doc_text">
780 <p>
781 The <code>RegionInfo</code> pass detects single entry single exit regions in a
782 function, where a region is defined as any subgraph that is connected to the
783 remaining graph at only two spots. Furthermore, an hierarchical region tree is
784 built.
785 </p>
786</div>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]787
788<!-------------------------------------------------------------------------- -->
789<div class="doc_subsection">
790 <a name="scalar-evolution">-scalar-evolution: Scalar Evolution Analysis</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]791</div>
792<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]793 <p>
794 The <code>ScalarEvolution</code> analysis can be used to analyze and
795 catagorize scalar expressions in loops. It specializes in recognizing general
796 induction variables, representing them with the abstract and opaque
797 <code>SCEV</code> class. Given this analysis, trip counts of loops and other
798 important properties can be obtained.
799 </p>
800
801 <p>
802 This analysis is primarily useful for induction variable substitution and
803 strength reduction.
804 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]805</div>
806
807<!-------------------------------------------------------------------------- -->
808<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]809 <a name="scev-aa">-scev-aa: </a>
810</div>
811<div class="doc_text">
812 <p>Simple alias analysis implemented in terms of ScalarEvolution queries.
813
814 This differs from traditional loop dependence analysis in that it tests
815 for dependencies within a single iteration of a loop, rather than
816 dependencies between different iterations.
817
818 ScalarEvolution has a more complete understanding of pointer arithmetic
819 than BasicAliasAnalysis' collection of ad-hoc analyses.
820 </p>
821</div>
822
823<!-------------------------------------------------------------------------- -->
824<div class="doc_subsection">
825 <a name="strip-dead-debug-info">-strip-dead-debug-info: Strip debug info for unused symbols</a>
826</div>
827<div class="doc_text">
828 <p>
829 performs code stripping. this transformation can delete:
830 </p>
831
832 <ol>
833 <li>names for virtual registers</li>
834 <li>symbols for internal globals and functions</li>
835 <li>debug information</li>
836 </ol>
837
838 <p>
839 note that this transformation makes code much less readable, so it should
840 only be used in situations where the <tt>strip</tt> utility would be used,
841 such as reducing code size or making it harder to reverse engineer code.
842 </p>
843</div>
844
845<!-------------------------------------------------------------------------- -->
846<div class="doc_subsection">
847 <a name="targetdata">-targetdata: Target Data Layout</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]848</div>
849<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]850 <p>Provides other passes access to information on how the size and alignment
851 required by the the target ABI for various data types.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]852</div>
853
854<!-- ======================================================================= -->
855<div class="doc_section"> <a name="transform">Transform Passes</a></div>
856<div class="doc_text">
857 <p>This section describes the LLVM Transform Passes.</p>
858</div>
859
860<!-------------------------------------------------------------------------- -->
861<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]862 <a name="abcd">-abcd: Remove redundant conditional branches</a>
863</div>
864<div class="doc_text">
865 <p>ABCD removes conditional branch instructions that can be proved redundant.
866 With the SSI representation, each variable has a constraint. By analyzing these
867 constraints we can prove that a branch is redundant. When a branch is proved
868 redundant it means that one direction will always be taken; thus, we can change
869 this branch into an unconditional jump.</p>
870 <p>It is advisable to run <a href="#simplifycfg">SimplifyCFG</a> and
871 <a href="#adce">Aggressive Dead Code Elimination</a> after ABCD
872 to clean up the code.</p>
873</div>
874
875<!-------------------------------------------------------------------------- -->
876<div class="doc_subsection">
877 <a name="adce">-adce: Aggressive Dead Code Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]878</div>
879<div class="doc_text">
880 <p>ADCE aggressively tries to eliminate code. This pass is similar to
881 <a href="#dce">DCE</a> but it assumes that values are dead until proven
882 otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
883 the liveness of values.</p>
884</div>
885
886<!-------------------------------------------------------------------------- -->
887<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]888 <a name="always-inline">-always-inline: Inliner for always_inline functions</a>
889</div>
890<div class="doc_text">
891 <p>A custom inliner that handles only functions that are marked as
892 "always inline".</p>
893</div>
894
895<!-------------------------------------------------------------------------- -->
896<div class="doc_subsection">
897 <a name="argpromotion">-argpromotion: Promote 'by reference' arguments to scalars</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]898</div>
899<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]900 <p>
901 This pass promotes "by reference" arguments to be "by value" arguments. In
902 practice, this means looking for internal functions that have pointer
903 arguments. If it can prove, through the use of alias analysis, that an
904 argument is *only* loaded, then it can pass the value into the function
905 instead of the address of the value. This can cause recursive simplification
906 of code and lead to the elimination of allocas (especially in C++ template
907 code like the STL).
908 </p>
909
910 <p>
911 This pass also handles aggregate arguments that are passed into a function,
912 scalarizing them if the elements of the aggregate are only loaded. Note that
913 it refuses to scalarize aggregates which would require passing in more than
914 three operands to the function, because passing thousands of operands for a
915 large array or structure is unprofitable!
916 </p>
917
918 <p>
919 Note that this transformation could also be done for arguments that are only
920 stored to (returning the value instead), but does not currently. This case
921 would be best handled when and if LLVM starts supporting multiple return
922 values from functions.
923 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]924</div>
925
926<!-------------------------------------------------------------------------- -->
927<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]928 <a name="block-placement">-block-placement: Profile Guided Basic Block Placement</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]929</div>
930<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]931 <p>This pass is a very simple profile guided basic block placement algorithm.
932 The idea is to put frequently executed blocks together at the start of the
933 function and hopefully increase the number of fall-through conditional
934 branches. If there is no profile information for a particular function, this
935 pass basically orders blocks in depth-first order.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]936</div>
937
938<!-------------------------------------------------------------------------- -->
939<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]940 <a name="break-crit-edges">-break-crit-edges: Break critical edges in CFG</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]941</div>
942<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]943 <p>
944 Break all of the critical edges in the CFG by inserting a dummy basic block.
945 It may be "required" by passes that cannot deal with critical edges. This
946 transformation obviously invalidates the CFG, but can update forward dominator
947 (set, immediate dominators, tree, and frontier) information.
948 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]949</div>
950
951<!-------------------------------------------------------------------------- -->
952<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]953 <a name="codegenprepare">-codegenprepare: Prepare a function for code generation</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]954</div>
955<div class="doc_text">
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]956 This pass munges the code in the input function to better prepare it for
957 SelectionDAG-based code generation. This works around limitations in it's
958 basic-block-at-a-time approach. It should eventually be removed.
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]959</div>
960
961<!-------------------------------------------------------------------------- -->
962<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]963 <a name="constmerge">-constmerge: Merge Duplicate Global Constants</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]964</div>
965<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]966 <p>
967 Merges duplicate global constants together into a single constant that is
968 shared. This is useful because some passes (ie TraceValues) insert a lot of
969 string constants into the program, regardless of whether or not an existing
970 string is available.
971 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]972</div>
973
974<!-------------------------------------------------------------------------- -->
975<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]976 <a name="constprop">-constprop: Simple constant propagation</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]977</div>
978<div class="doc_text">
979 <p>This file implements constant propagation and merging. It looks for
980 instructions involving only constant operands and replaces them with a
Gordon Henriksenbd412212007-10-25 08:58:56 +0000[diff] [blame]981 constant value instead of an instruction. For example:</p>
982 <blockquote><pre>add i32 1, 2</pre></blockquote>
983 <p>becomes</p>
984 <blockquote><pre>i32 3</pre></blockquote>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]985 <p>NOTE: this pass has a habit of making definitions be dead. It is a good
986 idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
987 sometime after running this pass.</p>
988</div>
989
990<!-------------------------------------------------------------------------- -->
991<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]992 <a name="dce">-dce: Dead Code Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]993</div>
994<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]995 <p>
996 Dead code elimination is similar to <a href="#die">dead instruction
997 elimination</a>, but it rechecks instructions that were used by removed
998 instructions to see if they are newly dead.
999 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1000</div>
1001
1002<!-------------------------------------------------------------------------- -->
1003<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1004 <a name="deadargelim">-deadargelim: Dead Argument Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1005</div>
1006<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1007 <p>
1008 This pass deletes dead arguments from internal functions. Dead argument
1009 elimination removes arguments which are directly dead, as well as arguments
1010 only passed into function calls as dead arguments of other functions. This
1011 pass also deletes dead arguments in a similar way.
1012 </p>
1013
1014 <p>
1015 This pass is often useful as a cleanup pass to run after aggressive
1016 interprocedural passes, which add possibly-dead arguments.
1017 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1018</div>
1019
1020<!-------------------------------------------------------------------------- -->
1021<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1022 <a name="deadtypeelim">-deadtypeelim: Dead Type Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1023</div>
1024<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1025 <p>
1026 This pass is used to cleanup the output of GCC. It eliminate names for types
1027 that are unused in the entire translation unit, using the <a
1028 href="#findusedtypes">find used types</a> pass.
1029 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1030</div>
1031
1032<!-------------------------------------------------------------------------- -->
1033<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1034 <a name="die">-die: Dead Instruction Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1035</div>
1036<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1037 <p>
1038 Dead instruction elimination performs a single pass over the function,
1039 removing instructions that are obviously dead.
1040 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1041</div>
1042
1043<!-------------------------------------------------------------------------- -->
1044<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1045 <a name="dse">-dse: Dead Store Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1046</div>
1047<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1048 <p>
1049 A trivial dead store elimination that only considers basic-block local
1050 redundant stores.
1051 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1052</div>
1053
1054<!-------------------------------------------------------------------------- -->
1055<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1056 <a name="functionattrs">-functionattrs: Deduce function attributes</a>
1057</div>
1058<div class="doc_text">
1059 <p>A simple interprocedural pass which walks the call-graph, looking for
1060 functions which do not access or only read non-local memory, and marking them
1061 readnone/readonly. In addition, it marks function arguments (of pointer type)
1062 'nocapture' if a call to the function does not create any copies of the pointer
1063 value that outlive the call. This more or less means that the pointer is only
1064 dereferenced, and not returned from the function or stored in a global.
1065 This pass is implemented as a bottom-up traversal of the call-graph.
1066 </p>
1067</div>
1068
1069<!-------------------------------------------------------------------------- -->
1070<div class="doc_subsection">
1071 <a name="globaldce">-globaldce: Dead Global Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1072</div>
1073<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1074 <p>
1075 This transform is designed to eliminate unreachable internal globals from the
1076 program. It uses an aggressive algorithm, searching out globals that are
1077 known to be alive. After it finds all of the globals which are needed, it
1078 deletes whatever is left over. This allows it to delete recursive chunks of
1079 the program which are unreachable.
1080 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1081</div>
1082
1083<!-------------------------------------------------------------------------- -->
1084<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1085 <a name="globalopt">-globalopt: Global Variable Optimizer</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1086</div>
1087<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1088 <p>
1089 This pass transforms simple global variables that never have their address
1090 taken. If obviously true, it marks read/write globals as constant, deletes
1091 variables only stored to, etc.
1092 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1093</div>
1094
1095<!-------------------------------------------------------------------------- -->
1096<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1097 <a name="gvn">-gvn: Global Value Numbering</a>
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]1098</div>
1099<div class="doc_text">
1100 <p>
Chris Lattner2bb49c32009-10-10 18:40:48 +0000[diff] [blame]1101 This pass performs global value numbering to eliminate fully and partially
1102 redundant instructions. It also performs redundant load elimination.
Matthijs Kooijman9aac1db2008-06-05 07:55:49 +0000[diff] [blame]1103 </p>
Gordon Henriksen951bc792007-10-25 10:18:27 +0000[diff] [blame]1104</div>
1105
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]1106<!-------------------------------------------------------------------------- -->
1107<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1108 <a name="indvars">-indvars: Canonicalize Induction Variables</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1109</div>
1110<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1111 <p>
1112 This transformation analyzes and transforms the induction variables (and
1113 computations derived from them) into simpler forms suitable for subsequent
1114 analysis and transformation.
1115 </p>
1116
1117 <p>
1118 This transformation makes the following changes to each loop with an
1119 identifiable induction variable:
1120 </p>
1121
1122 <ol>
1123 <li>All loops are transformed to have a <em>single</em> canonical
1124 induction variable which starts at zero and steps by one.</li>
1125 <li>The canonical induction variable is guaranteed to be the first PHI node
1126 in the loop header block.</li>
1127 <li>Any pointer arithmetic recurrences are raised to use array
1128 subscripts.</li>
1129 </ol>
1130
1131 <p>
1132 If the trip count of a loop is computable, this pass also makes the following
1133 changes:
1134 </p>
1135
1136 <ol>
1137 <li>The exit condition for the loop is canonicalized to compare the
1138 induction value against the exit value. This turns loops like:
1139 <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
1140 into
1141 <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
1142 <li>Any use outside of the loop of an expression derived from the indvar
1143 is changed to compute the derived value outside of the loop, eliminating
1144 the dependence on the exit value of the induction variable. If the only
1145 purpose of the loop is to compute the exit value of some derived
1146 expression, this transformation will make the loop dead.</li>
Gordon Henriksenbc39fe62007-11-04 16:17:00 +0000[diff] [blame]1147 </ol>
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1148
1149 <p>
1150 This transformation should be followed by strength reduction after all of the
1151 desired loop transformations have been performed. Additionally, on targets
1152 where it is profitable, the loop could be transformed to count down to zero
1153 (the "do loop" optimization).
1154 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1155</div>
1156
1157<!-------------------------------------------------------------------------- -->
1158<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1159 <a name="inline">-inline: Function Integration/Inlining</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1160</div>
1161<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1162 <p>
1163 Bottom-up inlining of functions into callees.
1164 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1165</div>
1166
1167<!-------------------------------------------------------------------------- -->
1168<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1169 <a name="insert-edge-profiling">-insert-edge-profiling: Insert instrumentation for edge profiling</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1170</div>
1171<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1172 <p>
1173 This pass instruments the specified program with counters for edge profiling.
1174 Edge profiling can give a reasonable approximation of the hot paths through a
1175 program, and is used for a wide variety of program transformations.
1176 </p>
1177
1178 <p>
1179 Note that this implementation is very naïve. It inserts a counter for
1180 <em>every</em> edge in the program, instead of using control flow information
1181 to prune the number of counters inserted.
1182 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1183</div>
1184
1185<!-------------------------------------------------------------------------- -->
1186<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1187 <a name="insert-optimal-edge-profiling">-insert-optimal-edge-profiling: Insert optimal instrumentation for edge profiling</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1188</div>
1189<div class="doc_text">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1190 <p>This pass instruments the specified program with counters for edge profiling.
1191 Edge profiling can give a reasonable approximation of the hot paths through a
1192 program, and is used for a wide variety of program transformations.
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1193 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1194</div>
1195
1196<!-------------------------------------------------------------------------- -->
1197<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1198 <a name="instcombine">-instcombine: Combine redundant instructions</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1199</div>
1200<div class="doc_text">
Gordon Henriksen9adadb42007-10-26 03:03:51 +0000[diff] [blame]1201 <p>
1202 Combine instructions to form fewer, simple
1203 instructions. This pass does not modify the CFG This pass is where algebraic
1204 simplification happens.
1205 </p>
1206
1207 <p>
1208 This pass combines things like:
1209 </p>
1210
1211<blockquote><pre
1212>%Y = add i32 %X, 1
1213%Z = add i32 %Y, 1</pre></blockquote>
1214
1215 <p>
1216 into:
1217 </p>
1218
1219<blockquote><pre
1220>%Z = add i32 %X, 2</pre></blockquote>
1221
1222 <p>
1223 This is a simple worklist driven algorithm.
1224 </p>
1225
1226 <p>
1227 This pass guarantees that the following canonicalizations are performed on
1228 the program:
1229 </p>
1230
1231 <ul>
1232 <li>If a binary operator has a constant operand, it is moved to the right-
1233 hand side.</li>
1234 <li>Bitwise operators with constant operands are always grouped so that
1235 shifts are performed first, then <code>or</code>s, then
1236 <code>and</code>s, then <code>xor</code>s.</li>
1237 <li>Compare instructions are converted from <code>&lt;</code>,
1238 <code>&gt;</code>, <code>≤</code>, or <code>≥</code> to
1239 <code>=</code> or <code>≠</code> if possible.</li>
1240 <li>All <code>cmp</code> instructions on boolean values are replaced with
1241 logical operations.</li>
1242 <li><code>add <var>X</var>, <var>X</var></code> is represented as
1243 <code>mul <var>X</var>, 2</code> ⇒ <code>shl <var>X</var>, 1</code></li>
1244 <li>Multiplies with a constant power-of-two argument are transformed into
1245 shifts.</li>
1246 <li>… etc.</li>
1247 </ul>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1248</div>
1249
1250<!-------------------------------------------------------------------------- -->
1251<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1252 <a name="internalize">-internalize: Internalize Global Symbols</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1253</div>
1254<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1255 <p>
1256 This pass loops over all of the functions in the input module, looking for a
1257 main function. If a main function is found, all other functions and all
1258 global variables with initializers are marked as internal.
1259 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1260</div>
1261
1262<!-------------------------------------------------------------------------- -->
1263<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1264 <a name="ipconstprop">-ipconstprop: Interprocedural constant propagation</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1265</div>
1266<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1267 <p>
1268 This pass implements an <em>extremely</em> simple interprocedural constant
1269 propagation pass. It could certainly be improved in many different ways,
1270 like using a worklist. This pass makes arguments dead, but does not remove
1271 them. The existing dead argument elimination pass should be run after this
1272 to clean up the mess.
1273 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1274</div>
1275
1276<!-------------------------------------------------------------------------- -->
1277<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1278 <a name="ipsccp">-ipsccp: Interprocedural Sparse Conditional Constant Propagation</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1279</div>
1280<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1281 <p>
1282 An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
1283 Propagation</a>.
1284 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1285</div>
1286
1287<!-------------------------------------------------------------------------- -->
1288<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1289 <a name="jump-threading">-jump-threading: Thread control through conditional blocks</a>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]1290</div>
1291<div class="doc_text">
1292 <p>
1293 Jump threading tries to find distinct threads of control flow running through
1294 a basic block. This pass looks at blocks that have multiple predecessors and
1295 multiple successors. If one or more of the predecessors of the block can be
1296 proven to always cause a jump to one of the successors, we forward the edge
1297 from the predecessor to the successor by duplicating the contents of this
1298 block.
1299 </p>
1300 <p>
1301 An example of when this can occur is code like this:
1302 </p>
1303
1304 <pre
1305>if () { ...
1306 X = 4;
1307}
1308if (X &lt; 3) {</pre>
1309
1310 <p>
1311 In this case, the unconditional branch at the end of the first if can be
1312 revectored to the false side of the second if.
1313 </p>
1314</div>
1315
1316<!-------------------------------------------------------------------------- -->
1317<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1318 <a name="lcssa">-lcssa: Loop-Closed SSA Form Pass</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1319</div>
1320<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1321 <p>
1322 This pass transforms loops by placing phi nodes at the end of the loops for
1323 all values that are live across the loop boundary. For example, it turns
1324 the left into the right code:
1325 </p>
1326
1327 <pre
1328>for (...) for (...)
1329 if (c) if (c)
1330 X1 = ... X1 = ...
1331 else else
1332 X2 = ... X2 = ...
1333 X3 = phi(X1, X2) X3 = phi(X1, X2)
1334... = X3 + 4 X4 = phi(X3)
1335 ... = X4 + 4</pre>
1336
1337 <p>
1338 This is still valid LLVM; the extra phi nodes are purely redundant, and will
1339 be trivially eliminated by <code>InstCombine</code>. The major benefit of
1340 this transformation is that it makes many other loop optimizations, such as
1341 LoopUnswitching, simpler.
1342 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1343</div>
1344
1345<!-------------------------------------------------------------------------- -->
1346<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1347 <a name="licm">-licm: Loop Invariant Code Motion</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1348</div>
1349<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1350 <p>
1351 This pass performs loop invariant code motion, attempting to remove as much
1352 code from the body of a loop as possible. It does this by either hoisting
1353 code into the preheader block, or by sinking code to the exit blocks if it is
1354 safe. This pass also promotes must-aliased memory locations in the loop to
1355 live in registers, thus hoisting and sinking "invariant" loads and stores.
1356 </p>
1357
1358 <p>
1359 This pass uses alias analysis for two purposes:
1360 </p>
1361
1362 <ul>
1363 <li>Moving loop invariant loads and calls out of loops. If we can determine
1364 that a load or call inside of a loop never aliases anything stored to,
1365 we can hoist it or sink it like any other instruction.</li>
1366 <li>Scalar Promotion of Memory - If there is a store instruction inside of
1367 the loop, we try to move the store to happen AFTER the loop instead of
1368 inside of the loop. This can only happen if a few conditions are true:
1369 <ul>
1370 <li>The pointer stored through is loop invariant.</li>
1371 <li>There are no stores or loads in the loop which <em>may</em> alias
1372 the pointer. There are no calls in the loop which mod/ref the
1373 pointer.</li>
1374 </ul>
1375 If these conditions are true, we can promote the loads and stores in the
1376 loop of the pointer to use a temporary alloca'd variable. We then use
1377 the mem2reg functionality to construct the appropriate SSA form for the
1378 variable.</li>
1379 </ul>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1380</div>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]1381<!-------------------------------------------------------------------------- -->
1382<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1383 <a name="loop-deletion">-loop-deletion: Dead Loop Deletion Pass</a>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]1384</div>
1385<div class="doc_text">
1386 <p>
1387 This file implements the Dead Loop Deletion Pass. This pass is responsible
1388 for eliminating loops with non-infinite computable trip counts that have no
1389 side effects or volatile instructions, and do not contribute to the
1390 computation of the function's return value.
1391 </p>
1392</div>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1393
1394<!-------------------------------------------------------------------------- -->
1395<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1396 <a name="loop-extract">-loop-extract: Extract loops into new functions</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1397</div>
1398<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1399 <p>
1400 A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
1401 extract each top-level loop into its own new function. If the loop is the
1402 <em>only</em> loop in a given function, it is not touched. This is a pass most
1403 useful for debugging via bugpoint.
1404 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1405</div>
1406
1407<!-------------------------------------------------------------------------- -->
1408<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1409 <a name="loop-extract-single">-loop-extract-single: Extract at most one loop into a new function</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1410</div>
1411<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1412 <p>
1413 Similar to <a href="#loop-extract">Extract loops into new functions</a>,
1414 this pass extracts one natural loop from the program into a function if it
1415 can. This is used by bugpoint.
1416 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1417</div>
1418
1419<!-------------------------------------------------------------------------- -->
1420<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1421 <a name="loop-index-split">-loop-index-split: Index Split Loops</a>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]1422</div>
1423<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1424 <p>
1425 This pass divides loop's iteration range by spliting loop such that each
1426 individual loop is executed efficiently.
1427 </p>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]1428</div>
1429
1430<!-------------------------------------------------------------------------- -->
1431<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1432 <a name="loop-reduce">-loop-reduce: Loop Strength Reduction</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1433</div>
1434<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1435 <p>
1436 This pass performs a strength reduction on array references inside loops that
1437 have as one or more of their components the loop induction variable. This is
1438 accomplished by creating a new value to hold the initial value of the array
1439 access for the first iteration, and then creating a new GEP instruction in
1440 the loop to increment the value by the appropriate amount.
1441 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1442</div>
1443
1444<!-------------------------------------------------------------------------- -->
1445<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1446 <a name="loop-rotate">-loop-rotate: Rotate Loops</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1447</div>
1448<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1449 <p>A simple loop rotation transformation.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1450</div>
1451
1452<!-------------------------------------------------------------------------- -->
1453<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1454 <a name="loop-unroll">-loop-unroll: Unroll loops</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1455</div>
1456<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1457 <p>
1458 This pass implements a simple loop unroller. It works best when loops have
1459 been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
1460 allowing it to determine the trip counts of loops easily.
1461 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1462</div>
1463
1464<!-------------------------------------------------------------------------- -->
1465<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1466 <a name="loop-unswitch">-loop-unswitch: Unswitch loops</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1467</div>
1468<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1469 <p>
1470 This pass transforms loops that contain branches on loop-invariant conditions
1471 to have multiple loops. For example, it turns the left into the right code:
1472 </p>
1473
1474 <pre
1475>for (...) if (lic)
1476 A for (...)
1477 if (lic) A; B; C
1478 B else
1479 C for (...)
1480 A; C</pre>
1481
1482 <p>
1483 This can increase the size of the code exponentially (doubling it every time
1484 a loop is unswitched) so we only unswitch if the resultant code will be
1485 smaller than a threshold.
1486 </p>
1487
1488 <p>
1489 This pass expects LICM to be run before it to hoist invariant conditions out
1490 of the loop, to make the unswitching opportunity obvious.
1491 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1492</div>
1493
1494<!-------------------------------------------------------------------------- -->
1495<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1496 <a name="loopsimplify">-loopsimplify: Canonicalize natural loops</a>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]1497</div>
1498<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1499 <p>
1500 This pass performs several transformations to transform natural loops into a
1501 simpler form, which makes subsequent analyses and transformations simpler and
1502 more effective.
1503 </p>
1504
1505 <p>
1506 Loop pre-header insertion guarantees that there is a single, non-critical
1507 entry edge from outside of the loop to the loop header. This simplifies a
1508 number of analyses and transformations, such as LICM.
1509 </p>
1510
1511 <p>
1512 Loop exit-block insertion guarantees that all exit blocks from the loop
1513 (blocks which are outside of the loop that have predecessors inside of the
1514 loop) only have predecessors from inside of the loop (and are thus dominated
1515 by the loop header). This simplifies transformations such as store-sinking
1516 that are built into LICM.
1517 </p>
1518
1519 <p>
1520 This pass also guarantees that loops will have exactly one backedge.
1521 </p>
1522
1523 <p>
1524 Note that the simplifycfg pass will clean up blocks which are split out but
1525 end up being unnecessary, so usage of this pass should not pessimize
1526 generated code.
1527 </p>
1528
1529 <p>
1530 This pass obviously modifies the CFG, but updates loop information and
1531 dominator information.
1532 </p>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]1533</div>
1534
1535<!-------------------------------------------------------------------------- -->
1536<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1537 <a name="lowerallocs">-lowerallocs: Lower allocations from instructions to calls</a>
1538</div>
1539<div class="doc_text">
1540 <p>
1541 Turn <tt>malloc</tt> and <tt>free</tt> instructions into <tt>@malloc</tt> and
1542 <tt>@free</tt> calls.
1543 </p>
1544
1545 <p>
1546 This is a target-dependent tranformation because it depends on the size of
1547 data types and alignment constraints.
1548 </p>
1549</div>
1550
1551<!-------------------------------------------------------------------------- -->
1552<div class="doc_subsection">
Peter Collingbourne948d9a52010-08-03 16:19:16 +0000[diff] [blame^]1553 <a name="loweratomic">-loweratomic: Lower atomic intrinsics
1554</div>
1555<div class="doc_text">
1556 <p>
1557 This pass lowers atomic intrinsics to non-atomic form for use in a known
1558 non-preemptible environment.
1559 </p>
1560
1561 <p>
1562 The pass does not verify that the environment is non-preemptible (in
1563 general this would require knowledge of the entire call graph of the
1564 program including any libraries which may not be available in bitcode form);
1565 it simply lowers every atomic intrinsic.
1566 </p>
1567</div>
1568
1569<!-------------------------------------------------------------------------- -->
1570<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1571 <a name="lowerinvoke">-lowerinvoke: Lower invoke and unwind, for unwindless code generators</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1572</div>
1573<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1574 <p>
1575 This transformation is designed for use by code generators which do not yet
1576 support stack unwinding. This pass supports two models of exception handling
1577 lowering, the 'cheap' support and the 'expensive' support.
1578 </p>
1579
1580 <p>
1581 'Cheap' exception handling support gives the program the ability to execute
1582 any program which does not "throw an exception", by turning 'invoke'
1583 instructions into calls and by turning 'unwind' instructions into calls to
1584 abort(). If the program does dynamically use the unwind instruction, the
1585 program will print a message then abort.
1586 </p>
1587
1588 <p>
1589 'Expensive' exception handling support gives the full exception handling
1590 support to the program at the cost of making the 'invoke' instruction
1591 really expensive. It basically inserts setjmp/longjmp calls to emulate the
1592 exception handling as necessary.
1593 </p>
1594
1595 <p>
1596 Because the 'expensive' support slows down programs a lot, and EH is only
1597 used for a subset of the programs, it must be specifically enabled by the
1598 <tt>-enable-correct-eh-support</tt> option.
1599 </p>
1600
1601 <p>
1602 Note that after this pass runs the CFG is not entirely accurate (exceptional
1603 control flow edges are not correct anymore) so only very simple things should
1604 be done after the lowerinvoke pass has run (like generation of native code).
1605 This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
1606 support the invoke instruction yet" lowering pass.
1607 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1608</div>
1609
1610<!-------------------------------------------------------------------------- -->
1611<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1612 <a name="lowersetjmp">-lowersetjmp: Lower Set Jump</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1613</div>
1614<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1615 <p>
1616 Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
1617 instructions as necessary.
1618 </p>
1619
1620 <p>
1621 Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
1622 call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
1623 This unwinds the stack for us calling all of the destructors for
1624 objects allocated on the stack.
1625 </p>
1626
1627 <p>
1628 At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
1629 removed. The calls in a function that have a <tt>setjmp</tt> are converted to
1630 invoke where the except part checks to see if it's a <tt>longjmp</tt>
1631 exception and, if so, if it's handled in the function. If it is, then it gets
1632 the value returned by the <tt>longjmp</tt> and goes to where the basic block
1633 was split. <tt>invoke</tt> instructions are handled in a similar fashion with
1634 the original except block being executed if it isn't a <tt>longjmp</tt>
1635 except that is handled by that function.
1636 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1637</div>
1638
1639<!-------------------------------------------------------------------------- -->
1640<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1641 <a name="lowerswitch">-lowerswitch: Lower SwitchInst's to branches</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1642</div>
1643<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1644 <p>
1645 Rewrites <tt>switch</tt> instructions with a sequence of branches, which
1646 allows targets to get away with not implementing the switch instruction until
1647 it is convenient.
1648 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1649</div>
1650
1651<!-------------------------------------------------------------------------- -->
1652<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1653 <a name="mem2reg">-mem2reg: Promote Memory to Register</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1654</div>
1655<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1656 <p>
1657 This file promotes memory references to be register references. It promotes
1658 <tt>alloca</tt> instructions which only have <tt>load</tt>s and
1659 <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
1660 frontiers to place <tt>phi</tt> nodes, then traversing the function in
1661 depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
1662 appropriate. This is just the standard SSA construction algorithm to construct
1663 "pruned" SSA form.
1664 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1665</div>
1666
1667<!-------------------------------------------------------------------------- -->
1668<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1669 <a name="memcpyopt">-memcpyopt: Optimize use of memcpy and friend</a>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]1670</div>
1671<div class="doc_text">
1672 <p>
1673 This pass performs various transformations related to eliminating memcpy
1674 calls, or transforming sets of stores into memset's.
1675 </p>
1676</div>
1677
1678<!-------------------------------------------------------------------------- -->
1679<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1680 <a name="mergefunc">-mergefunc: Merge Functions</a>
1681</div>
1682<div class="doc_text">
1683 <p>This pass looks for equivalent functions that are mergable and folds them.
1684
1685 A hash is computed from the function, based on its type and number of
1686 basic blocks.
1687
1688 Once all hashes are computed, we perform an expensive equality comparison
1689 on each function pair. This takes n^2/2 comparisons per bucket, so it's
1690 important that the hash function be high quality. The equality comparison
1691 iterates through each instruction in each basic block.
1692
1693 When a match is found the functions are folded. If both functions are
1694 overridable, we move the functionality into a new internal function and
1695 leave two overridable thunks to it.
1696 </p>
1697</div>
1698
1699<!-------------------------------------------------------------------------- -->
1700<div class="doc_subsection">
1701 <a name="mergereturn">-mergereturn: Unify function exit nodes</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1702</div>
1703<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1704 <p>
1705 Ensure that functions have at most one <tt>ret</tt> instruction in them.
1706 Additionally, it keeps track of which node is the new exit node of the CFG.
1707 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1708</div>
1709
1710<!-------------------------------------------------------------------------- -->
1711<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1712 <a name="partial-inliner">-partial-inliner: Partial Inliner</a>
1713</div>
1714<div class="doc_text">
1715 <p>This pass performs partial inlining, typically by inlining an if
1716 statement that surrounds the body of the function.
1717 </p>
1718</div>
1719
1720<!-------------------------------------------------------------------------- -->
1721<div class="doc_subsection">
1722 <a name="partialspecialization">-partialspecialization: Partial Specialization</a>
1723</div>
1724<div class="doc_text">
1725 <p>This pass finds function arguments that are often a common constant and
1726 specializes a version of the called function for that constant.
1727
1728 This pass simply does the cloning for functions it specializes. It depends
1729 on <a href="#ipsccp">IPSCCP</a> and <a href="#deadargelim">DAE</a> to clean up the results.
1730
1731 The initial heuristic favors constant arguments that are used in control
1732 flow.
1733 </p>
1734</div>
1735
1736<!-------------------------------------------------------------------------- -->
1737<div class="doc_subsection">
1738 <a name="prune-eh">-prune-eh: Remove unused exception handling info</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1739</div>
1740<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1741 <p>
1742 This file implements a simple interprocedural pass which walks the call-graph,
1743 turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
1744 only if the callee cannot throw an exception. It implements this as a
1745 bottom-up traversal of the call-graph.
1746 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1747</div>
1748
1749<!-------------------------------------------------------------------------- -->
1750<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1751 <a name="reassociate">-reassociate: Reassociate expressions</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1752</div>
1753<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1754 <p>
1755 This pass reassociates commutative expressions in an order that is designed
1756 to promote better constant propagation, GCSE, LICM, PRE, etc.
1757 </p>
1758
1759 <p>
1760 For example: 4 + (<var>x</var> + 5) ⇒ <var>x</var> + (4 + 5)
1761 </p>
1762
1763 <p>
1764 In the implementation of this algorithm, constants are assigned rank = 0,
1765 function arguments are rank = 1, and other values are assigned ranks
1766 corresponding to the reverse post order traversal of current function
1767 (starting at 2), which effectively gives values in deep loops higher rank
1768 than values not in loops.
1769 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1770</div>
1771
1772<!-------------------------------------------------------------------------- -->
1773<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1774 <a name="reg2mem">-reg2mem: Demote all values to stack slots</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1775</div>
1776<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1777 <p>
1778 This file demotes all registers to memory references. It is intented to be
1779 the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
Benjamin Kramer5fb9d7e2009-10-12 14:46:08 +0000[diff] [blame]1780 <tt>load</tt> instructions, the only values live across basic blocks are
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1781 <tt>alloca</tt> instructions and <tt>load</tt> instructions before
1782 <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
1783 easier. To make later hacking easier, the entry block is split into two, such
1784 that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
1785 entry block.
1786 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1787</div>
1788
1789<!-------------------------------------------------------------------------- -->
1790<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1791 <a name="scalarrepl">-scalarrepl: Scalar Replacement of Aggregates</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1792</div>
1793<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1794 <p>
1795 The well-known scalar replacement of aggregates transformation. This
1796 transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
1797 or array) into individual <tt>alloca</tt> instructions for each member if
1798 possible. Then, if possible, it transforms the individual <tt>alloca</tt>
1799 instructions into nice clean scalar SSA form.
1800 </p>
1801
1802 <p>
1803 This combines a simple scalar replacement of aggregates algorithm with the <a
1804 href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
1805 especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
1806 then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
1807 promote works well.
1808 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1809</div>
1810
1811<!-------------------------------------------------------------------------- -->
1812<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1813 <a name="sccp">-sccp: Sparse Conditional Constant Propagation</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1814</div>
1815<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1816 <p>
1817 Sparse conditional constant propagation and merging, which can be summarized
1818 as:
1819 </p>
1820
1821 <ol>
1822 <li>Assumes values are constant unless proven otherwise</li>
1823 <li>Assumes BasicBlocks are dead unless proven otherwise</li>
1824 <li>Proves values to be constant, and replaces them with constants</li>
1825 <li>Proves conditional branches to be unconditional</li>
1826 </ol>
1827
1828 <p>
1829 Note that this pass has a habit of making definitions be dead. It is a good
1830 idea to to run a DCE pass sometime after running this pass.
1831 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1832</div>
1833
1834<!-------------------------------------------------------------------------- -->
1835<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1836 <a name="sink">-sink: Code Sinking</a>
1837</div>
1838<div class="doc_text">
1839 <p>This pass moves instructions into successor blocks, when possible, so that
1840 they aren't executed on paths where their results aren't needed.
1841 </p>
1842</div>
1843
1844<!-------------------------------------------------------------------------- -->
1845<div class="doc_subsection">
1846 <a name="simplify-libcalls">-simplify-libcalls: Simplify well-known library calls</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1847</div>
1848<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1849 <p>
1850 Applies a variety of small optimizations for calls to specific well-known
1851 function calls (e.g. runtime library functions). For example, a call
1852 <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
1853 transformed into simply <tt>return 3</tt>.
1854 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1855</div>
1856
1857<!-------------------------------------------------------------------------- -->
1858<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1859 <a name="simplify-libcalls-halfpowr">-simplify-libcalls-halfpowr: Simplify half_powr library calls</a>
1860</div>
1861<div class="doc_text">
1862 <p>Simple pass that applies an experimental transformation on calls
1863 to specific functions.
1864 </p>
1865</div>
1866
1867<!-------------------------------------------------------------------------- -->
1868<div class="doc_subsection">
1869 <a name="simplifycfg">-simplifycfg: Simplify the CFG</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1870</div>
1871<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1872 <p>
1873 Performs dead code elimination and basic block merging. Specifically:
1874 </p>
1875
1876 <ol>
1877 <li>Removes basic blocks with no predecessors.</li>
1878 <li>Merges a basic block into its predecessor if there is only one and the
1879 predecessor only has one successor.</li>
1880 <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
1881 <li>Eliminates a basic block that only contains an unconditional
1882 branch.</li>
1883 </ol>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1884</div>
1885
1886<!-------------------------------------------------------------------------- -->
1887<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1888 <a name="split-geps">-split-geps: Split complex GEPs into simple GEPs</a>
1889</div>
1890<div class="doc_text">
1891 <p>This function breaks GEPs with more than 2 non-zero operands into smaller
1892 GEPs each with no more than 2 non-zero operands. This exposes redundancy
1893 between GEPs with common initial operand sequences.
1894 </p>
1895</div>
1896
1897<!-------------------------------------------------------------------------- -->
1898<div class="doc_subsection">
1899 <a name="ssi">-ssi: Static Single Information Construction</a>
1900</div>
1901<div class="doc_text">
1902 <p>This pass converts a list of variables to the Static Single Information
1903 form.
1904
1905 We are building an on-demand representation, that is, we do not convert
1906 every single variable in the target function to SSI form. Rather, we receive
1907 a list of target variables that must be converted. We also do not
1908 completely convert a target variable to the SSI format. Instead, we only
1909 change the variable in the points where new information can be attached
1910 to its live range, that is, at branch points.
1911 </p>
1912</div>
1913
1914<!-------------------------------------------------------------------------- -->
1915<div class="doc_subsection">
1916 <a name="ssi-everything">-ssi-everything: Static Single Information Construction (everything, intended for debugging)</a>
1917</div>
1918<div class="doc_text">
1919 <p>A pass that runs <a href="#ssi">SSI</a> on every non-void variable, intended for debugging.
1920 </p>
1921</div>
1922
1923<!-------------------------------------------------------------------------- -->
1924<div class="doc_subsection">
1925 <a name="strip">-strip: Strip all symbols from a module</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1926</div>
1927<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1928 <p>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1929 performs code stripping. this transformation can delete:
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1930 </p>
1931
1932 <ol>
1933 <li>names for virtual registers</li>
1934 <li>symbols for internal globals and functions</li>
1935 <li>debug information</li>
1936 </ol>
1937
1938 <p>
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1939 note that this transformation makes code much less readable, so it should
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]1940 only be used in situations where the <tt>strip</tt> utility would be used,
1941 such as reducing code size or making it harder to reverse engineer code.
1942 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]1943</div>
1944
1945<!-------------------------------------------------------------------------- -->
1946<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1947 <a name="strip-dead-prototypes">-strip-dead-prototypes: Remove unused function declarations</a>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]1948</div>
1949<div class="doc_text">
1950 <p>
1951 This pass loops over all of the functions in the input module, looking for
1952 dead declarations and removes them. Dead declarations are declarations of
1953 functions for which no implementation is available (i.e., declarations for
1954 unused library functions).
1955 </p>
1956</div>
1957
1958<!-------------------------------------------------------------------------- -->
1959<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]1960 <a name="strip-debug-declare">-strip-debug-declare: Strip all llvm.dbg.declare intrinsics</a>
1961</div>
1962<div class="doc_text">
1963 <p>This pass implements code stripping. Specifically, it can delete:
1964 <ul>
1965 <li>names for virtual registers</li>
1966 <li>symbols for internal globals and functions</li>
1967 <li>debug information</li>
1968 </ul>
1969 Note that this transformation makes code much less readable, so it should
1970 only be used in situations where the 'strip' utility would be used, such as
1971 reducing code size or making it harder to reverse engineer code.
1972 </p>
1973</div>
1974
1975<!-------------------------------------------------------------------------- -->
1976<div class="doc_subsection">
1977 <a name="strip-nondebug">-strip-nondebug: Strip all symbols, except dbg symbols, from a module</a>
1978</div>
1979<div class="doc_text">
1980 <p>This pass implements code stripping. Specifically, it can delete:
1981 <ul>
1982 <li>names for virtual registers</li>
1983 <li>symbols for internal globals and functions</li>
1984 <li>debug information</li>
1985 </ul>
1986 Note that this transformation makes code much less readable, so it should
1987 only be used in situations where the 'strip' utility would be used, such as
1988 reducing code size or making it harder to reverse engineer code.
1989 </p>
1990</div>
1991
1992<!-------------------------------------------------------------------------- -->
1993<div class="doc_subsection">
1994 <a name="sretpromotion">-sretpromotion: Promote sret arguments</a>
Gordon Henriksen08556692008-05-08 17:46:35 +0000[diff] [blame]1995</div>
1996<div class="doc_text">
1997 <p>
1998 This pass finds functions that return a struct (using a pointer to the struct
1999 as the first argument of the function, marked with the '<tt>sret</tt>' attribute) and
2000 replaces them with a new function that simply returns each of the elements of
2001 that struct (using multiple return values).
2002 </p>
2003
2004 <p>
2005 This pass works under a number of conditions:
2006 </p>
2007
2008 <ul>
2009 <li>The returned struct must not contain other structs</li>
2010 <li>The returned struct must only be used to load values from</li>
2011 <li>The placeholder struct passed in is the result of an <tt>alloca</tt></li>
2012 </ul>
2013</div>
2014
2015<!-------------------------------------------------------------------------- -->
2016<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2017 <a name="tailcallelim">-tailcallelim: Tail Call Elimination</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2018</div>
2019<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]2020 <p>
2021 This file transforms calls of the current function (self recursion) followed
2022 by a return instruction with a branch to the entry of the function, creating
2023 a loop. This pass also implements the following extensions to the basic
2024 algorithm:
2025 </p>
2026
2027 <ul>
2028 <li>Trivial instructions between the call and return do not prevent the
2029 transformation from taking place, though currently the analysis cannot
2030 support moving any really useful instructions (only dead ones).
2031 <li>This pass transforms functions that are prevented from being tail
2032 recursive by an associative expression to use an accumulator variable,
2033 thus compiling the typical naive factorial or <tt>fib</tt> implementation
2034 into efficient code.
2035 <li>TRE is performed if the function returns void, if the return
2036 returns the result returned by the call, or if the function returns a
2037 run-time constant on all exits from the function. It is possible, though
2038 unlikely, that the return returns something else (like constant 0), and
2039 can still be TRE'd. It can be TRE'd if <em>all other</em> return
2040 instructions in the function return the exact same value.
2041 <li>If it can prove that callees do not access theier caller stack frame,
2042 they are marked as eligible for tail call elimination (by the code
2043 generator).
2044 </ul>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2045</div>
2046
2047<!-------------------------------------------------------------------------- -->
2048<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2049 <a name="tailduplicate">-tailduplicate: Tail Duplication</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2050</div>
2051<div class="doc_text">
Gordon Henriksen79ed5872007-11-04 16:15:04 +0000[diff] [blame]2052 <p>
2053 This pass performs a limited form of tail duplication, intended to simplify
2054 CFGs by removing some unconditional branches. This pass is necessary to
2055 straighten out loops created by the C front-end, but also is capable of
2056 making other code nicer. After this pass is run, the CFG simplify pass
2057 should be run to clean up the mess.
2058 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2059</div>
2060
2061<!-- ======================================================================= -->
2062<div class="doc_section"> <a name="transform">Utility Passes</a></div>
2063<div class="doc_text">
2064 <p>This section describes the LLVM Utility Passes.</p>
2065</div>
2066
2067<!-------------------------------------------------------------------------- -->
2068<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2069 <a name="deadarghaX0r">-deadarghaX0r: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2070</div>
2071<div class="doc_text">
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2072 <p>
2073 Same as dead argument elimination, but deletes arguments to functions which
2074 are external. This is only for use by <a
2075 href="Bugpoint.html">bugpoint</a>.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2076</div>
2077
2078<!-------------------------------------------------------------------------- -->
2079<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2080 <a name="extract-blocks">-extract-blocks: Extract Basic Blocks From Module (for bugpoint use)</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2081</div>
2082<div class="doc_text">
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2083 <p>
2084 This pass is used by bugpoint to extract all blocks from the module into their
2085 own functions.</p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2086</div>
2087
2088<!-------------------------------------------------------------------------- -->
2089<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2090 <a name="instnamer">-instnamer: Assign names to anonymous instructions</a>
2091</div>
2092<div class="doc_text">
2093 <p>This is a little utility pass that gives instructions names, this is mostly
2094 useful when diffing the effect of an optimization because deleting an
2095 unnamed instruction can change all other instruction numbering, making the
2096 diff very noisy.
2097 </p>
2098</div>
2099
2100<!-------------------------------------------------------------------------- -->
2101<div class="doc_subsection">
2102 <a name="preverify">-preverify: Preliminary module verification</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2103</div>
2104<div class="doc_text">
Gordon Henriksene88510a2007-11-05 02:05:35 +0000[diff] [blame]2105 <p>
2106 Ensures that the module is in the form required by the <a
2107 href="#verifier">Module Verifier</a> pass.
2108 </p>
2109
2110 <p>
2111 Running the verifier runs this pass automatically, so there should be no need
2112 to use it directly.
2113 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2114</div>
2115
2116<!-------------------------------------------------------------------------- -->
2117<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2118 <a name="verify">-verify: Module Verifier</a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2119</div>
2120<div class="doc_text">
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2121 <p>
2122 Verifies an LLVM IR code. This is useful to run after an optimization which is
2123 undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
2124 emitting bitcode, and also that malformed bitcode is likely to make LLVM
2125 crash. All language front-ends are therefore encouraged to verify their output
2126 before performing optimizing transformations.
2127 </p>
2128
Gordon Henriksenbf2b50b2007-11-04 18:14:08 +0000[diff] [blame]2129 <ul>
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2130 <li>Both of a binary operator's parameters are of the same type.</li>
2131 <li>Verify that the indices of mem access instructions match other
2132 operands.</li>
2133 <li>Verify that arithmetic and other things are only performed on
2134 first-class types. Verify that shifts and logicals only happen on
2135 integrals f.e.</li>
2136 <li>All of the constants in a switch statement are of the correct type.</li>
2137 <li>The code is in valid SSA form.</li>
Chris Lattnerd22ec1c2009-10-28 04:47:06 +0000[diff] [blame]2138 <li>It is illegal to put a label into any other type (like a structure) or
2139 to return one.</li>
Nick Lewycky56ae4fc2008-03-28 06:46:51 +0000[diff] [blame]2140 <li>Only phi nodes can be self referential: <tt>%x = add i32 %x, %x</tt> is
Gordon Henriksenb3327382007-11-04 18:17:58 +0000[diff] [blame]2141 invalid.</li>
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2142 <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
2143 <li>PHI nodes must be the first thing in a basic block, all grouped
2144 together.</li>
2145 <li>PHI nodes must have at least one entry.</li>
2146 <li>All basic blocks should only end with terminator insts, not contain
2147 them.</li>
2148 <li>The entry node to a function must not have predecessors.</li>
2149 <li>All Instructions must be embedded into a basic block.</li>
2150 <li>Functions cannot take a void-typed parameter.</li>
2151 <li>Verify that a function's argument list agrees with its declared
2152 type.</li>
2153 <li>It is illegal to specify a name for a void value.</li>
2154 <li>It is illegal to have a internal global value with no initializer.</li>
2155 <li>It is illegal to have a ret instruction that returns a value that does
2156 not agree with the function return value type.</li>
2157 <li>Function call argument types match the function prototype.</li>
2158 <li>All other things that are tested by asserts spread about the code.</li>
Gordon Henriksenbf2b50b2007-11-04 18:14:08 +0000[diff] [blame]2159 </ul>
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2160
2161 <p>
2162 Note that this does not provide full security verification (like Java), but
2163 instead just tries to ensure that code is well-formed.
2164 </p>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2165</div>
2166
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]2167<!-------------------------------------------------------------------------- -->
2168<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2169 <a name="view-cfg">-view-cfg: View CFG of function</a>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]2170</div>
2171<div class="doc_text">
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2172 <p>
2173 Displays the control flow graph using the GraphViz tool.
2174 </p>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]2175</div>
2176
2177<!-------------------------------------------------------------------------- -->
2178<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2179 <a name="view-cfg-only">-view-cfg-only: View CFG of function (with no function bodies)</a>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]2180</div>
2181<div class="doc_text">
Gordon Henrikseneabb3952007-11-04 18:10:18 +0000[diff] [blame]2182 <p>
2183 Displays the control flow graph using the GraphViz tool, but omitting function
2184 bodies.
2185 </p>
Gordon Henriksen9c2c7032007-10-25 08:46:12 +0000[diff] [blame]2186</div>
2187
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]2188<!-------------------------------------------------------------------------- -->
2189<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2190 <a name="view-dom">-view-dom: View dominator tree of function</a>
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]2191</div>
2192<div class="doc_text">
2193 <p>
2194 Displays the dominator tree using the GraphViz tool.
2195 </p>
2196</div>
2197
2198<!-------------------------------------------------------------------------- -->
2199<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2200 <a name="view-dom-only">-view-dom-only: View dominator tree of function (with no function
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]2201 bodies)
2202 </a>
2203</div>
2204<div class="doc_text">
2205 <p>
2206 Displays the dominator tree using the GraphViz tool, but omitting function
2207 bodies.
2208 </p>
2209</div>
2210
2211<!-------------------------------------------------------------------------- -->
2212<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2213 <a name="view-postdom">-view-postdom: View post dominator tree of function</a>
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]2214</div>
2215<div class="doc_text">
2216 <p>
2217 Displays the post dominator tree using the GraphViz tool.
2218 </p>
2219</div>
2220
2221<!-------------------------------------------------------------------------- -->
2222<div class="doc_subsection">
Duncan Sandsf90c5442010-07-06 15:52:15 +0000[diff] [blame]2223 <a name="view-postdom-only">-view-postdom-only: View post dominator tree of function (with no
Tobias Grosserc9700032010-05-07 09:33:18 +0000[diff] [blame]2224 function bodies)
2225 </a>
2226</div>
2227<div class="doc_text">
2228 <p>
2229 Displays the post dominator tree using the GraphViz tool, but omitting
2230 function bodies.
2231 </p>
2232</div>
2233
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2234<!-- *********************************************************************** -->
2235
2236<hr>
2237<address>
2238 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman947321d2008-12-11 17:34:48 +0000[diff] [blame]2239 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2240 <a href="http://validator.w3.org/check/referer"><img
Misha Brukman947321d2008-12-11 17:34:48 +0000[diff] [blame]2241 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
Dan Gohmanf17a25c2007-07-18 16:29:46 +0000[diff] [blame]2242
2243 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
2244 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
2245 Last modified: $Date$
2246</address>
2247
2248</body>
2249</html>