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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 0b8f0a208e9849c7ea50173b98acb51efbe1f2c7 / . / docs / Passes.html
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Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3<html>
4<head>
5 <title>LLVM's Analysis and Transform Passes</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]7 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]8</head>
9<body>
10
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]11<!--
12
13If Passes.html is up to date, the following "one-liner" should print
14an empty diff.
15
16egrep -e '^<tr><td><a href="#.*">-.*</a></td><td>.*</td></tr>$' \
17 -e '^ <a name=".*">.*</a>$' < Passes.html >html; \
18perl >help <<'EOT' && diff -u help html; rm -f help html
19open HTML, "<Passes.html" or die "open: Passes.html: $!\n";
20while (<HTML>) {
21 m:^<tr><td><a href="#(.*)">-.*</a></td><td>.*</td></tr>$: or next;
22 $order{$1} = sprintf("%03d", 1 + int %order);
23}
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]24open HELP, "../Release/bin/opt -help|" or die "open: opt -help: $!\n";
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]25while (<HELP>) {
26 m:^ -([^ ]+) +- (.*)$: or next;
27 my $o = $order{$1};
28 $o = "000" unless defined $o;
29 push @x, "$o<tr><td><a href=\"#$1\">-$1</a></td><td>$2</td></tr>\n";
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]30 push @y, "$o <a name=\"$1\">-$1: $2</a>\n";
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]31}
32@x = map { s/^\d\d\d//; $_ } sort @x;
33@y = map { s/^\d\d\d//; $_ } sort @y;
34print @x, @y;
35EOT
36
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]37This (real) one-liner can also be helpful when converting comments to HTML:
38
39perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print " <p>\n" if !$on && $_ =~ /\S/; print " </p>\n" if $on && $_ =~ /^\s*$/; print " $_\n"; $on = ($_ =~ /\S/); } print " </p>\n" if $on'
40
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]41 -->
42
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]43<div class="doc_title">LLVM's Analysis and Transform Passes</div>
44
45<ol>
46 <li><a href="#intro">Introduction</a></li>
47 <li><a href="#analyses">Analysis Passes</a>
48 <li><a href="#transforms">Transform Passes</a></li>
49 <li><a href="#utilities">Utility Passes</a></li>
50</ol>
51
52<div class="doc_author">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]53 <p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
54 and Gordon Henriksen</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]55</div>
56
57<!-- ======================================================================= -->
58<div class="doc_section"> <a name="intro">Introduction</a> </div>
59<div class="doc_text">
60 <p>This document serves as a high level summary of the optimization features
61 that LLVM provides. Optimizations are implemented as Passes that traverse some
62 portion of a program to either collect information or transform the program.
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]63 The table below divides the passes that LLVM provides into three categories.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]64 Analysis passes compute information that other passes can use or for debugging
65 or program visualization purposes. Transform passes can use (or invalidate)
66 the analysis passes. Transform passes all mutate the program in some way.
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]67 Utility passes provides some utility but don't otherwise fit categorization.
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]68 For example passes to extract functions to bitcode or write a module to
69 bitcode are neither analysis nor transform passes.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]70 <p>The table below provides a quick summary of each pass and links to the more
71 complete pass description later in the document.</p>
72</div>
73<div class="doc_text" >
74<table>
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]75<tr><th colspan="2"><b>ANALYSIS PASSES</b></th></tr>
76<tr><th>Option</th><th>Name</th></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]77<tr><td><a href="#aa-eval">-aa-eval</a></td><td>Exhaustive Alias Analysis Precision Evaluator</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]78<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (default AA impl)</td></tr>
79<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]80<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]81<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
82<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
83<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]84<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]85<tr><td><a href="#dot-callgraph">-dot-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
86<tr><td><a href="#dot-cfg">-dot-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
87<tr><td><a href="#dot-cfg-only">-dot-cfg-only</a></td><td>Print CFG of function to 'dot' file (with no function bodies)</td></tr>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]88<tr><td><a href="#dot-dom">-dot-dom</a></td><td>Print dominator tree of function to 'dot' file</td></tr>
89<tr><td><a href="#dot-dom-only">-dot-dom-only</a></td><td>Print dominator tree of function to 'dot' file (with no function bodies)</td></tr>
90<tr><td><a href="#dot-postdom">-dot-postdom</a></td><td>Print post dominator tree of function to 'dot' file</td></tr>
91<tr><td><a href="#dot-postdom-only">-dot-postdom-only</a></td><td>Print post dominator tree of function to 'dot' file (with no function bodies)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]92<tr><td><a href="#globalsmodref-aa">-globalsmodref-aa</a></td><td>Simple mod/ref analysis for globals</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]93<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]94<tr><td><a href="#interprocedural-aa-eval">-interprocedural-aa-eval</a></td><td>Exhaustive Interprocedural Alias Analysis Precision Evaluator</td></tr>
95<tr><td><a href="#interprocedural-basic-aa">-interprocedural-basic-aa</a></td><td>Interprocedural Basic Alias Analysis</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]96<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]97<tr><td><a href="#iv-users">-iv-users</a></td><td>Induction Variable Users</td></tr>
98<tr><td><a href="#lazy-value-info">-lazy-value-info</a></td><td>Lazy Value Information Analysis</td></tr>
99<tr><td><a href="#lda">-lda</a></td><td>Loop Dependence Analysis</td></tr>
100<tr><td><a href="#libcall-aa">-libcall-aa</a></td><td>LibCall Alias Analysis</td></tr>
101<tr><td><a href="#lint">-lint</a></td><td>Check for common errors in LLVM IR</td></tr>
102<tr><td><a href="#live-values">-live-values</a></td><td>Value Liveness Analysis</td></tr>
103<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Information</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]104<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]105<tr><td><a href="#module-debuginfo">-module-debuginfo</a></td><td>Prints module debug info metadata</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]106<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
107<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]108<tr><td><a href="#pointertracking">-pointertracking</a></td><td>Track pointer bounds</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]109<tr><td><a href="#postdomfrontier">-postdomfrontier</a></td><td>Post-Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]110<tr><td><a href="#postdomtree">-postdomtree</a></td><td>Post-Dominator Tree Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]111<tr><td><a href="#print-alias-sets">-print-alias-sets</a></td><td>Alias Set Printer</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]112<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
113<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
114<tr><td><a href="#print-cfg-sccs">-print-cfg-sccs</a></td><td>Print SCCs of each function CFG</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]115<tr><td><a href="#print-dbginfo">-print-dbginfo</a></td><td>Print debug info in human readable form</td></tr>
116<tr><td><a href="#print-dom-info">-print-dom-info</a></td><td>Dominator Info Printer</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]117<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
118<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
119<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
120<tr><td><a href="#print-used-types">-print-used-types</a></td><td>Find Used Types</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]121<tr><td><a href="#profile-estimator">-profile-estimator</a></td><td>Estimate profiling information</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]122<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
Tobias Grosserf96b0062010-07-22 07:46:31 +0000[diff] [blame]123<tr><td><a href="#regions">-regions</a></td><td>Detect single entry single exit regions in a function</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]124<tr><td><a href="#profile-verifier">-profile-verifier</a></td><td>Verify profiling information</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]125<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]126<tr><td><a href="#scev-aa">-scev-aa</a></td><td>ScalarEvolution-based Alias Analysis</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]127<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
128
129
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]130<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
131<tr><th>Option</th><th>Name</th></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]132<tr><td><a href="#abcd">-abcd</a></td><td>Remove redundant conditional branches</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]133<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]134<tr><td><a href="#always-inline">-always-inline</a></td><td>Inliner for always_inline functions</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]135<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
136<tr><td><a href="#block-placement">-block-placement</a></td><td>Profile Guided Basic Block Placement</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]137<tr><td><a href="#break-crit-edges">-break-crit-edges</a></td><td>Break critical edges in CFG</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]138<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Prepare a function for code generation </td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]139<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
140<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
141<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
142<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
143<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
144<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
145<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]146<tr><td><a href="#functionattrs">-functionattrs</a></td><td>Deduce function attributes</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]147<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
148<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]149<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]150<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
151<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]152<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]153<tr><td><a href="#insert-optimal-edge-profiling">-insert-optimal-edge-profiling</a></td><td>Insert optimal instrumentation for edge profiling</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]154<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
155<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
156<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
157<tr><td><a href="#ipsccp">-ipsccp</a></td><td>Interprocedural Sparse Conditional Constant Propagation</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]158<tr><td><a href="#jump-threading">-jump-threading</a></td><td>Thread control through conditional blocks </td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]159<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
160<tr><td><a href="#licm">-licm</a></td><td>Loop Invariant Code Motion</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]161<tr><td><a href="#loop-deletion">-loop-deletion</a></td><td>Dead Loop Deletion Pass </td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]162<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
163<tr><td><a href="#loop-extract-single">-loop-extract-single</a></td><td>Extract at most one loop into a new function</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]164<tr><td><a href="#loop-index-split">-loop-index-split</a></td><td>Index Split Loops</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]165<tr><td><a href="#loop-reduce">-loop-reduce</a></td><td>Loop Strength Reduction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]166<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
167<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
168<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
169<tr><td><a href="#loopsimplify">-loopsimplify</a></td><td>Canonicalize natural loops</td></tr>
Peter Collingbourne3bababf2010-08-03 16:19:16 +0000[diff] [blame]170<tr><td><a href="#loweratomic">-loweratomic</a></td><td>Lower atomic intrinsics</td></tr>
Gordon Henriksen1f5cce02007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +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 Henriksena8a118b2008-05-08 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]176<tr><td><a href="#mergefunc">-mergefunc</a></td><td>Merge Functions</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]177<tr><td><a href="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
Duncan Sands5c603862010-07-06 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]180<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]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>
Reid Spencerd9aac122007-03-26 09:32:31 +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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]185<tr><td><a href="#sink">-sink</a></td><td>Code Sinking</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]186<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]187<tr><td><a href="#simplify-libcalls-halfpowr">-simplify-libcalls-halfpowr</a></td><td>Simplify half_powr library calls</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]188<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
Duncan Sands5c603862010-07-06 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]192<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]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 Henriksena8a118b2008-05-08 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 Sands5c603862010-07-06 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 Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]197<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +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 Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]200
201
Gordon Henriksenddaa61d2007-10-25 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 Henriksen1f5cce02007-10-25 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]206<tr><td><a href="#instnamer">-instnamer</a></td><td>Assign names to anonymous instructions</td></tr>
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]207<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]208<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
Gordon Henriksen1f5cce02007-10-25 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 Grosser733783b2010-05-07 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>
Reid Spencerd9aac122007-03-26 09:32:31 +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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]226 <a name="aa-eval">-aa-eval: Exhaustive Alias Analysis Precision Evaluator</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]227</div>
228<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]236</div>
237
238<!-------------------------------------------------------------------------- -->
239<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]240 <a name="basicaa">-basicaa: Basic Alias Analysis (default AA impl)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]241</div>
242<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]248</div>
249
250<!-------------------------------------------------------------------------- -->
251<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]252 <a name="basiccg">-basiccg: Basic CallGraph Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]260 <a name="codegenprepare">-codegenprepare: Optimize for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]261</div>
262<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]268</div>
269
270<!-------------------------------------------------------------------------- -->
271<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]272 <a name="count-aa">-count-aa: Count Alias Analysis Query Responses</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]273</div>
274<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]279</div>
280
281<!-------------------------------------------------------------------------- -->
282<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]283 <a name="debug-aa">-debug-aa: AA use debugger</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]284</div>
285<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]296</div>
297
298<!-------------------------------------------------------------------------- -->
299<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]300 <a name="domfrontier">-domfrontier: Dominance Frontier Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]301</div>
302<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]307</div>
308
309<!-------------------------------------------------------------------------- -->
310<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]311 <a name="domtree">-domtree: Dominator Tree Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]312</div>
313<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]314 <p>
315 This pass is a simple dominator construction algorithm for finding forward
316 dominators.
317 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]318</div>
319
320<!-------------------------------------------------------------------------- -->
321<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]322 <a name="dot-callgraph">-dot-callgraph: Print Call Graph to 'dot' file</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]323</div>
324<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]325 <p>
Duncan Sands3ee8fc92008-09-23 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]334 <a name="dot-cfg">-dot-cfg: Print CFG of function to 'dot' file</a>
Duncan Sands3ee8fc92008-09-23 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 Sands5c603862010-07-06 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 Sands3ee8fc92008-09-23 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 Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]354 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]355</div>
356
357<!-------------------------------------------------------------------------- -->
358<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]359 <a name="dot-dom">-dot-dom: Print dominator tree of function to 'dot' file</a>
Tobias Grosser733783b2010-05-07 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 Sands5c603862010-07-06 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 Grosser733783b2010-05-07 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">
Tobias Grosser03057242010-10-21 21:16:03 +0000[diff] [blame]385 <a name="dot-postdom">-dot-postdom: Print post dominator tree of function to 'dot' file</a>
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]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">
Tobias Grosser03057242010-10-21 21:16:03 +0000[diff] [blame]397 <a name="dot-postdom-only">-dot-postdom-only: Print post dominator tree of function to 'dot' file
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]411 <a name="globalsmodref-aa">-globalsmodref-aa: Simple mod/ref analysis for globals</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]412</div>
413<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]420</div>
421
422<!-------------------------------------------------------------------------- -->
423<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]424 <a name="instcount">-instcount: Counts the various types of Instructions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]425</div>
426<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]427 <p>
428 This pass collects the count of all instructions and reports them
429 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]430</div>
431
432<!-------------------------------------------------------------------------- -->
433<div class="doc_subsection">
Duncan Sands5c603862010-07-06 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]458</div>
459<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]469</div>
470
471<!-------------------------------------------------------------------------- -->
472<div class="doc_subsection">
Duncan Sands5c603862010-07-06 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]547</div>
548<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]555</div>
556
557<!-------------------------------------------------------------------------- -->
558<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]559 <a name="memdep">-memdep: Memory Dependence Analysis</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]560</div>
561<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 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 Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]568</div>
569
570<!-------------------------------------------------------------------------- -->
571<div class="doc_subsection">
Duncan Sands5c603862010-07-06 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]586</div>
587<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]593</div>
594
595<!-------------------------------------------------------------------------- -->
596<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]597 <a name="no-profile">-no-profile: No Profile Information</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]598</div>
599<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]600 <p>
601 The default "no profile" implementation of the abstract
602 <code>ProfileInfo</code> interface.
603 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]604</div>
605
606<!-------------------------------------------------------------------------- -->
607<div class="doc_subsection">
Duncan Sands5c603862010-07-06 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]618</div>
619<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]624</div>
625
626<!-------------------------------------------------------------------------- -->
627<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]628 <a name="postdomtree">-postdomtree: Post-Dominator Tree Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]629</div>
630<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]635</div>
636
637<!-------------------------------------------------------------------------- -->
638<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]639 <a name="print-alias-sets">-print-alias-sets: Alias Set Printer</a>
Duncan Sands3ee8fc92008-09-23 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]647 <a name="print-callgraph">-print-callgraph: Print a call graph</a>
Duncan Sands3ee8fc92008-09-23 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
Dan Gohman52fdaed2010-08-20 01:03:44 +0000[diff] [blame]652 standard error in a human-readable form.
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]653 </p>
654</div>
655
656<!-------------------------------------------------------------------------- -->
657<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]658 <a name="print-callgraph-sccs">-print-callgraph-sccs: Print SCCs of the Call Graph</a>
Duncan Sands3ee8fc92008-09-23 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
Dan Gohman52fdaed2010-08-20 01:03:44 +0000[diff] [blame]663 graph to standard error in a human-readable form.
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]664 </p>
665</div>
666
667<!-------------------------------------------------------------------------- -->
668<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]669 <a name="print-cfg-sccs">-print-cfg-sccs: Print SCCs of each function CFG</a>
Duncan Sands3ee8fc92008-09-23 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
Dan Gohman52fdaed2010-08-20 01:03:44 +0000[diff] [blame]674 function CFG to standard error in a human-readable form.
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]675 </p>
676</div>
677
678<!-------------------------------------------------------------------------- -->
679<div class="doc_subsection">
Duncan Sands5c603862010-07-06 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">
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]683 <p>Pass that prints instructions, and associated debug info:</p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]684 <ul>
685
686 <li>source/line/col information</li>
687 <li>original variable name</li>
688 <li>original type name</li>
689 </ul>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]690</div>
691
692<!-------------------------------------------------------------------------- -->
693<div class="doc_subsection">
694 <a name="print-dom-info">-print-dom-info: Dominator Info Printer</a>
695</div>
696<div class="doc_text">
697 <p>Dominator Info Printer.</p>
698</div>
699
700<!-------------------------------------------------------------------------- -->
701<div class="doc_subsection">
702 <a name="print-externalfnconstants">-print-externalfnconstants: Print external fn callsites passed constants</a>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]703</div>
704<div class="doc_text">
705 <p>
706 This pass, only available in <code>opt</code>, prints out call sites to
707 external functions that are called with constant arguments. This can be
708 useful when looking for standard library functions we should constant fold
709 or handle in alias analyses.
710 </p>
711</div>
712
713<!-------------------------------------------------------------------------- -->
714<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]715 <a name="print-function">-print-function: Print function to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]716</div>
717<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]718 <p>
719 The <code>PrintFunctionPass</code> class is designed to be pipelined with
720 other <code>FunctionPass</code>es, and prints out the functions of the module
721 as they are processed.
722 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]723</div>
724
725<!-------------------------------------------------------------------------- -->
726<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]727 <a name="print-module">-print-module: Print module to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]728</div>
729<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]730 <p>
731 This pass simply prints out the entire module when it is executed.
732 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]733</div>
734
735<!-------------------------------------------------------------------------- -->
736<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]737 <a name="print-used-types">-print-used-types: Find Used Types</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]738</div>
739<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]740 <p>
741 This pass is used to seek out all of the types in use by the program. Note
742 that this analysis explicitly does not include types only used by the symbol
743 table.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]744</div>
745
746<!-------------------------------------------------------------------------- -->
747<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]748 <a name="profile-estimator">-profile-estimator: Estimate profiling information</a>
749</div>
750<div class="doc_text">
751 <p>Profiling information that estimates the profiling information
752 in a very crude and unimaginative way.
753 </p>
754</div>
755
756<!-------------------------------------------------------------------------- -->
757<div class="doc_subsection">
758 <a name="profile-loader">-profile-loader: Load profile information from llvmprof.out</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]759</div>
760<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]761 <p>
762 A concrete implementation of profiling information that loads the information
763 from a profile dump file.
764 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]765</div>
766
767<!-------------------------------------------------------------------------- -->
768<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]769 <a name="profile-verifier">-profile-verifier: Verify profiling information</a>
770</div>
771<div class="doc_text">
772 <p>Pass that checks profiling information for plausibility.</p>
773</div>
Tobias Grosserf96b0062010-07-22 07:46:31 +0000[diff] [blame]774<div class="doc_subsection">
775 <a name="regions">-regions: Detect single entry single exit regions in a function</a>
776</div>
777<div class="doc_text">
778 <p>
779 The <code>RegionInfo</code> pass detects single entry single exit regions in a
780 function, where a region is defined as any subgraph that is connected to the
781 remaining graph at only two spots. Furthermore, an hierarchical region tree is
782 built.
783 </p>
784</div>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]785
786<!-------------------------------------------------------------------------- -->
787<div class="doc_subsection">
788 <a name="scalar-evolution">-scalar-evolution: Scalar Evolution Analysis</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]789</div>
790<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]791 <p>
792 The <code>ScalarEvolution</code> analysis can be used to analyze and
793 catagorize scalar expressions in loops. It specializes in recognizing general
794 induction variables, representing them with the abstract and opaque
795 <code>SCEV</code> class. Given this analysis, trip counts of loops and other
796 important properties can be obtained.
797 </p>
798
799 <p>
800 This analysis is primarily useful for induction variable substitution and
801 strength reduction.
802 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]803</div>
804
805<!-------------------------------------------------------------------------- -->
806<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]807 <a name="scev-aa">-scev-aa: </a>
808</div>
809<div class="doc_text">
810 <p>Simple alias analysis implemented in terms of ScalarEvolution queries.
811
812 This differs from traditional loop dependence analysis in that it tests
813 for dependencies within a single iteration of a loop, rather than
814 dependencies between different iterations.
815
816 ScalarEvolution has a more complete understanding of pointer arithmetic
817 than BasicAliasAnalysis' collection of ad-hoc analyses.
818 </p>
819</div>
820
821<!-------------------------------------------------------------------------- -->
822<div class="doc_subsection">
823 <a name="strip-dead-debug-info">-strip-dead-debug-info: Strip debug info for unused symbols</a>
824</div>
825<div class="doc_text">
826 <p>
827 performs code stripping. this transformation can delete:
828 </p>
829
830 <ol>
831 <li>names for virtual registers</li>
832 <li>symbols for internal globals and functions</li>
833 <li>debug information</li>
834 </ol>
835
836 <p>
837 note that this transformation makes code much less readable, so it should
838 only be used in situations where the <tt>strip</tt> utility would be used,
839 such as reducing code size or making it harder to reverse engineer code.
840 </p>
841</div>
842
843<!-------------------------------------------------------------------------- -->
844<div class="doc_subsection">
845 <a name="targetdata">-targetdata: Target Data Layout</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]846</div>
847<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]848 <p>Provides other passes access to information on how the size and alignment
849 required by the the target ABI for various data types.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]850</div>
851
852<!-- ======================================================================= -->
853<div class="doc_section"> <a name="transform">Transform Passes</a></div>
854<div class="doc_text">
855 <p>This section describes the LLVM Transform Passes.</p>
856</div>
857
858<!-------------------------------------------------------------------------- -->
859<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]860 <a name="abcd">-abcd: Remove redundant conditional branches</a>
861</div>
862<div class="doc_text">
863 <p>ABCD removes conditional branch instructions that can be proved redundant.
864 With the SSI representation, each variable has a constraint. By analyzing these
865 constraints we can prove that a branch is redundant. When a branch is proved
866 redundant it means that one direction will always be taken; thus, we can change
867 this branch into an unconditional jump.</p>
868 <p>It is advisable to run <a href="#simplifycfg">SimplifyCFG</a> and
869 <a href="#adce">Aggressive Dead Code Elimination</a> after ABCD
870 to clean up the code.</p>
871</div>
872
873<!-------------------------------------------------------------------------- -->
874<div class="doc_subsection">
875 <a name="adce">-adce: Aggressive Dead Code Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]876</div>
877<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]878 <p>ADCE aggressively tries to eliminate code. This pass is similar to
879 <a href="#dce">DCE</a> but it assumes that values are dead until proven
880 otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
881 the liveness of values.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]882</div>
883
884<!-------------------------------------------------------------------------- -->
885<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]886 <a name="always-inline">-always-inline: Inliner for always_inline functions</a>
887</div>
888<div class="doc_text">
889 <p>A custom inliner that handles only functions that are marked as
890 "always inline".</p>
891</div>
892
893<!-------------------------------------------------------------------------- -->
894<div class="doc_subsection">
895 <a name="argpromotion">-argpromotion: Promote 'by reference' arguments to scalars</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]896</div>
897<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]898 <p>
899 This pass promotes "by reference" arguments to be "by value" arguments. In
900 practice, this means looking for internal functions that have pointer
901 arguments. If it can prove, through the use of alias analysis, that an
902 argument is *only* loaded, then it can pass the value into the function
903 instead of the address of the value. This can cause recursive simplification
904 of code and lead to the elimination of allocas (especially in C++ template
905 code like the STL).
906 </p>
907
908 <p>
909 This pass also handles aggregate arguments that are passed into a function,
910 scalarizing them if the elements of the aggregate are only loaded. Note that
911 it refuses to scalarize aggregates which would require passing in more than
912 three operands to the function, because passing thousands of operands for a
913 large array or structure is unprofitable!
914 </p>
915
916 <p>
917 Note that this transformation could also be done for arguments that are only
918 stored to (returning the value instead), but does not currently. This case
919 would be best handled when and if LLVM starts supporting multiple return
920 values from functions.
921 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]922</div>
923
924<!-------------------------------------------------------------------------- -->
925<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]926 <a name="block-placement">-block-placement: Profile Guided Basic Block Placement</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]927</div>
928<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]929 <p>This pass is a very simple profile guided basic block placement algorithm.
930 The idea is to put frequently executed blocks together at the start of the
931 function and hopefully increase the number of fall-through conditional
932 branches. If there is no profile information for a particular function, this
933 pass basically orders blocks in depth-first order.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]934</div>
935
936<!-------------------------------------------------------------------------- -->
937<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]938 <a name="break-crit-edges">-break-crit-edges: Break critical edges in CFG</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]939</div>
940<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]941 <p>
942 Break all of the critical edges in the CFG by inserting a dummy basic block.
943 It may be "required" by passes that cannot deal with critical edges. This
944 transformation obviously invalidates the CFG, but can update forward dominator
945 (set, immediate dominators, tree, and frontier) information.
946 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]947</div>
948
949<!-------------------------------------------------------------------------- -->
950<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]951 <a name="codegenprepare">-codegenprepare: Prepare a function for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]952</div>
953<div class="doc_text">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]954 This pass munges the code in the input function to better prepare it for
955 SelectionDAG-based code generation. This works around limitations in it's
956 basic-block-at-a-time approach. It should eventually be removed.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]957</div>
958
959<!-------------------------------------------------------------------------- -->
960<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]961 <a name="constmerge">-constmerge: Merge Duplicate Global Constants</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]962</div>
963<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]964 <p>
965 Merges duplicate global constants together into a single constant that is
966 shared. This is useful because some passes (ie TraceValues) insert a lot of
967 string constants into the program, regardless of whether or not an existing
968 string is available.
969 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]970</div>
971
972<!-------------------------------------------------------------------------- -->
973<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]974 <a name="constprop">-constprop: Simple constant propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]975</div>
976<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]977 <p>This file implements constant propagation and merging. It looks for
978 instructions involving only constant operands and replaces them with a
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]979 constant value instead of an instruction. For example:</p>
980 <blockquote><pre>add i32 1, 2</pre></blockquote>
981 <p>becomes</p>
982 <blockquote><pre>i32 3</pre></blockquote>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]983 <p>NOTE: this pass has a habit of making definitions be dead. It is a good
984 idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
985 sometime after running this pass.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]986</div>
987
988<!-------------------------------------------------------------------------- -->
989<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]990 <a name="dce">-dce: Dead Code Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]991</div>
992<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]993 <p>
994 Dead code elimination is similar to <a href="#die">dead instruction
995 elimination</a>, but it rechecks instructions that were used by removed
996 instructions to see if they are newly dead.
997 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]998</div>
999
1000<!-------------------------------------------------------------------------- -->
1001<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1002 <a name="deadargelim">-deadargelim: Dead Argument Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1003</div>
1004<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1005 <p>
1006 This pass deletes dead arguments from internal functions. Dead argument
1007 elimination removes arguments which are directly dead, as well as arguments
1008 only passed into function calls as dead arguments of other functions. This
1009 pass also deletes dead arguments in a similar way.
1010 </p>
1011
1012 <p>
1013 This pass is often useful as a cleanup pass to run after aggressive
1014 interprocedural passes, which add possibly-dead arguments.
1015 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1016</div>
1017
1018<!-------------------------------------------------------------------------- -->
1019<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1020 <a name="deadtypeelim">-deadtypeelim: Dead Type Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1021</div>
1022<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1023 <p>
1024 This pass is used to cleanup the output of GCC. It eliminate names for types
1025 that are unused in the entire translation unit, using the <a
1026 href="#findusedtypes">find used types</a> pass.
1027 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1028</div>
1029
1030<!-------------------------------------------------------------------------- -->
1031<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1032 <a name="die">-die: Dead Instruction Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1033</div>
1034<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1035 <p>
1036 Dead instruction elimination performs a single pass over the function,
1037 removing instructions that are obviously dead.
1038 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1039</div>
1040
1041<!-------------------------------------------------------------------------- -->
1042<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1043 <a name="dse">-dse: Dead Store Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1044</div>
1045<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1046 <p>
1047 A trivial dead store elimination that only considers basic-block local
1048 redundant stores.
1049 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1050</div>
1051
1052<!-------------------------------------------------------------------------- -->
1053<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1054 <a name="functionattrs">-functionattrs: Deduce function attributes</a>
1055</div>
1056<div class="doc_text">
1057 <p>A simple interprocedural pass which walks the call-graph, looking for
1058 functions which do not access or only read non-local memory, and marking them
1059 readnone/readonly. In addition, it marks function arguments (of pointer type)
1060 'nocapture' if a call to the function does not create any copies of the pointer
1061 value that outlive the call. This more or less means that the pointer is only
1062 dereferenced, and not returned from the function or stored in a global.
1063 This pass is implemented as a bottom-up traversal of the call-graph.
1064 </p>
1065</div>
1066
1067<!-------------------------------------------------------------------------- -->
1068<div class="doc_subsection">
1069 <a name="globaldce">-globaldce: Dead Global Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1070</div>
1071<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1072 <p>
1073 This transform is designed to eliminate unreachable internal globals from the
1074 program. It uses an aggressive algorithm, searching out globals that are
1075 known to be alive. After it finds all of the globals which are needed, it
1076 deletes whatever is left over. This allows it to delete recursive chunks of
1077 the program which are unreachable.
1078 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1079</div>
1080
1081<!-------------------------------------------------------------------------- -->
1082<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1083 <a name="globalopt">-globalopt: Global Variable Optimizer</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1084</div>
1085<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1086 <p>
1087 This pass transforms simple global variables that never have their address
1088 taken. If obviously true, it marks read/write globals as constant, deletes
1089 variables only stored to, etc.
1090 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1091</div>
1092
1093<!-------------------------------------------------------------------------- -->
1094<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1095 <a name="gvn">-gvn: Global Value Numbering</a>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]1096</div>
1097<div class="doc_text">
1098 <p>
Chris Lattner60f03402009-10-10 18:40:48 +0000[diff] [blame]1099 This pass performs global value numbering to eliminate fully and partially
1100 redundant instructions. It also performs redundant load elimination.
Matthijs Kooijman845f5242008-06-05 07:55:49 +0000[diff] [blame]1101 </p>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]1102</div>
1103
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1104<!-------------------------------------------------------------------------- -->
1105<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1106 <a name="indvars">-indvars: Canonicalize Induction Variables</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1107</div>
1108<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1109 <p>
1110 This transformation analyzes and transforms the induction variables (and
1111 computations derived from them) into simpler forms suitable for subsequent
1112 analysis and transformation.
1113 </p>
1114
1115 <p>
1116 This transformation makes the following changes to each loop with an
1117 identifiable induction variable:
1118 </p>
1119
1120 <ol>
1121 <li>All loops are transformed to have a <em>single</em> canonical
1122 induction variable which starts at zero and steps by one.</li>
1123 <li>The canonical induction variable is guaranteed to be the first PHI node
1124 in the loop header block.</li>
1125 <li>Any pointer arithmetic recurrences are raised to use array
1126 subscripts.</li>
1127 </ol>
1128
1129 <p>
1130 If the trip count of a loop is computable, this pass also makes the following
1131 changes:
1132 </p>
1133
1134 <ol>
1135 <li>The exit condition for the loop is canonicalized to compare the
1136 induction value against the exit value. This turns loops like:
1137 <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
1138 into
1139 <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
1140 <li>Any use outside of the loop of an expression derived from the indvar
1141 is changed to compute the derived value outside of the loop, eliminating
1142 the dependence on the exit value of the induction variable. If the only
1143 purpose of the loop is to compute the exit value of some derived
1144 expression, this transformation will make the loop dead.</li>
Gordon Henriksene626bbe2007-11-04 16:17:00 +0000[diff] [blame]1145 </ol>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1146
1147 <p>
1148 This transformation should be followed by strength reduction after all of the
1149 desired loop transformations have been performed. Additionally, on targets
1150 where it is profitable, the loop could be transformed to count down to zero
1151 (the "do loop" optimization).
1152 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1153</div>
1154
1155<!-------------------------------------------------------------------------- -->
1156<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1157 <a name="inline">-inline: Function Integration/Inlining</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1158</div>
1159<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1160 <p>
1161 Bottom-up inlining of functions into callees.
1162 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1163</div>
1164
1165<!-------------------------------------------------------------------------- -->
1166<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1167 <a name="insert-edge-profiling">-insert-edge-profiling: Insert instrumentation for edge profiling</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1168</div>
1169<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1170 <p>
1171 This pass instruments the specified program with counters for edge profiling.
1172 Edge profiling can give a reasonable approximation of the hot paths through a
1173 program, and is used for a wide variety of program transformations.
1174 </p>
1175
1176 <p>
1177 Note that this implementation is very naïve. It inserts a counter for
1178 <em>every</em> edge in the program, instead of using control flow information
1179 to prune the number of counters inserted.
1180 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1181</div>
1182
1183<!-------------------------------------------------------------------------- -->
1184<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1185 <a name="insert-optimal-edge-profiling">-insert-optimal-edge-profiling: Insert optimal instrumentation for edge profiling</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1186</div>
1187<div class="doc_text">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1188 <p>This pass instruments the specified program with counters for edge profiling.
1189 Edge profiling can give a reasonable approximation of the hot paths through a
1190 program, and is used for a wide variety of program transformations.
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1191 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1192</div>
1193
1194<!-------------------------------------------------------------------------- -->
1195<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1196 <a name="instcombine">-instcombine: Combine redundant instructions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1197</div>
1198<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1199 <p>
1200 Combine instructions to form fewer, simple
1201 instructions. This pass does not modify the CFG This pass is where algebraic
1202 simplification happens.
1203 </p>
1204
1205 <p>
1206 This pass combines things like:
1207 </p>
1208
1209<blockquote><pre
1210>%Y = add i32 %X, 1
1211%Z = add i32 %Y, 1</pre></blockquote>
1212
1213 <p>
1214 into:
1215 </p>
1216
1217<blockquote><pre
1218>%Z = add i32 %X, 2</pre></blockquote>
1219
1220 <p>
1221 This is a simple worklist driven algorithm.
1222 </p>
1223
1224 <p>
1225 This pass guarantees that the following canonicalizations are performed on
1226 the program:
1227 </p>
1228
1229 <ul>
1230 <li>If a binary operator has a constant operand, it is moved to the right-
1231 hand side.</li>
1232 <li>Bitwise operators with constant operands are always grouped so that
1233 shifts are performed first, then <code>or</code>s, then
1234 <code>and</code>s, then <code>xor</code>s.</li>
1235 <li>Compare instructions are converted from <code>&lt;</code>,
1236 <code>&gt;</code>, <code>≤</code>, or <code>≥</code> to
1237 <code>=</code> or <code>≠</code> if possible.</li>
1238 <li>All <code>cmp</code> instructions on boolean values are replaced with
1239 logical operations.</li>
1240 <li><code>add <var>X</var>, <var>X</var></code> is represented as
1241 <code>mul <var>X</var>, 2</code> ⇒ <code>shl <var>X</var>, 1</code></li>
1242 <li>Multiplies with a constant power-of-two argument are transformed into
1243 shifts.</li>
1244 <li>… etc.</li>
1245 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1246</div>
1247
1248<!-------------------------------------------------------------------------- -->
1249<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1250 <a name="internalize">-internalize: Internalize Global Symbols</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1251</div>
1252<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1253 <p>
1254 This pass loops over all of the functions in the input module, looking for a
1255 main function. If a main function is found, all other functions and all
1256 global variables with initializers are marked as internal.
1257 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1258</div>
1259
1260<!-------------------------------------------------------------------------- -->
1261<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1262 <a name="ipconstprop">-ipconstprop: Interprocedural constant propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1263</div>
1264<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1265 <p>
1266 This pass implements an <em>extremely</em> simple interprocedural constant
1267 propagation pass. It could certainly be improved in many different ways,
1268 like using a worklist. This pass makes arguments dead, but does not remove
1269 them. The existing dead argument elimination pass should be run after this
1270 to clean up the mess.
1271 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1272</div>
1273
1274<!-------------------------------------------------------------------------- -->
1275<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1276 <a name="ipsccp">-ipsccp: Interprocedural Sparse Conditional Constant Propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1277</div>
1278<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1279 <p>
1280 An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
1281 Propagation</a>.
1282 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1283</div>
1284
1285<!-------------------------------------------------------------------------- -->
1286<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1287 <a name="jump-threading">-jump-threading: Thread control through conditional blocks</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1288</div>
1289<div class="doc_text">
1290 <p>
1291 Jump threading tries to find distinct threads of control flow running through
1292 a basic block. This pass looks at blocks that have multiple predecessors and
1293 multiple successors. If one or more of the predecessors of the block can be
1294 proven to always cause a jump to one of the successors, we forward the edge
1295 from the predecessor to the successor by duplicating the contents of this
1296 block.
1297 </p>
1298 <p>
1299 An example of when this can occur is code like this:
1300 </p>
1301
1302 <pre
1303>if () { ...
1304 X = 4;
1305}
1306if (X &lt; 3) {</pre>
1307
1308 <p>
1309 In this case, the unconditional branch at the end of the first if can be
1310 revectored to the false side of the second if.
1311 </p>
1312</div>
1313
1314<!-------------------------------------------------------------------------- -->
1315<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1316 <a name="lcssa">-lcssa: Loop-Closed SSA Form Pass</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1317</div>
1318<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1319 <p>
1320 This pass transforms loops by placing phi nodes at the end of the loops for
1321 all values that are live across the loop boundary. For example, it turns
1322 the left into the right code:
1323 </p>
1324
1325 <pre
1326>for (...) for (...)
1327 if (c) if (c)
1328 X1 = ... X1 = ...
1329 else else
1330 X2 = ... X2 = ...
1331 X3 = phi(X1, X2) X3 = phi(X1, X2)
1332... = X3 + 4 X4 = phi(X3)
1333 ... = X4 + 4</pre>
1334
1335 <p>
1336 This is still valid LLVM; the extra phi nodes are purely redundant, and will
1337 be trivially eliminated by <code>InstCombine</code>. The major benefit of
1338 this transformation is that it makes many other loop optimizations, such as
1339 LoopUnswitching, simpler.
1340 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1341</div>
1342
1343<!-------------------------------------------------------------------------- -->
1344<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1345 <a name="licm">-licm: Loop Invariant Code Motion</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1346</div>
1347<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1348 <p>
1349 This pass performs loop invariant code motion, attempting to remove as much
1350 code from the body of a loop as possible. It does this by either hoisting
1351 code into the preheader block, or by sinking code to the exit blocks if it is
1352 safe. This pass also promotes must-aliased memory locations in the loop to
1353 live in registers, thus hoisting and sinking "invariant" loads and stores.
1354 </p>
1355
1356 <p>
1357 This pass uses alias analysis for two purposes:
1358 </p>
1359
1360 <ul>
1361 <li>Moving loop invariant loads and calls out of loops. If we can determine
1362 that a load or call inside of a loop never aliases anything stored to,
1363 we can hoist it or sink it like any other instruction.</li>
1364 <li>Scalar Promotion of Memory - If there is a store instruction inside of
1365 the loop, we try to move the store to happen AFTER the loop instead of
1366 inside of the loop. This can only happen if a few conditions are true:
1367 <ul>
1368 <li>The pointer stored through is loop invariant.</li>
1369 <li>There are no stores or loads in the loop which <em>may</em> alias
1370 the pointer. There are no calls in the loop which mod/ref the
1371 pointer.</li>
1372 </ul>
1373 If these conditions are true, we can promote the loads and stores in the
1374 loop of the pointer to use a temporary alloca'd variable. We then use
1375 the mem2reg functionality to construct the appropriate SSA form for the
1376 variable.</li>
1377 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1378</div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1379<!-------------------------------------------------------------------------- -->
1380<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1381 <a name="loop-deletion">-loop-deletion: Dead Loop Deletion Pass</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1382</div>
1383<div class="doc_text">
1384 <p>
1385 This file implements the Dead Loop Deletion Pass. This pass is responsible
1386 for eliminating loops with non-infinite computable trip counts that have no
1387 side effects or volatile instructions, and do not contribute to the
1388 computation of the function's return value.
1389 </p>
1390</div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1391
1392<!-------------------------------------------------------------------------- -->
1393<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1394 <a name="loop-extract">-loop-extract: Extract loops into new functions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1395</div>
1396<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1397 <p>
1398 A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
1399 extract each top-level loop into its own new function. If the loop is the
1400 <em>only</em> loop in a given function, it is not touched. This is a pass most
1401 useful for debugging via bugpoint.
1402 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1403</div>
1404
1405<!-------------------------------------------------------------------------- -->
1406<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1407 <a name="loop-extract-single">-loop-extract-single: Extract at most one loop into a new function</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1408</div>
1409<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1410 <p>
1411 Similar to <a href="#loop-extract">Extract loops into new functions</a>,
1412 this pass extracts one natural loop from the program into a function if it
1413 can. This is used by bugpoint.
1414 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1415</div>
1416
1417<!-------------------------------------------------------------------------- -->
1418<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1419 <a name="loop-index-split">-loop-index-split: Index Split Loops</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1420</div>
1421<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1422 <p>
1423 This pass divides loop's iteration range by spliting loop such that each
1424 individual loop is executed efficiently.
1425 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1426</div>
1427
1428<!-------------------------------------------------------------------------- -->
1429<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1430 <a name="loop-reduce">-loop-reduce: Loop Strength Reduction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1431</div>
1432<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1433 <p>
1434 This pass performs a strength reduction on array references inside loops that
1435 have as one or more of their components the loop induction variable. This is
1436 accomplished by creating a new value to hold the initial value of the array
1437 access for the first iteration, and then creating a new GEP instruction in
1438 the loop to increment the value by the appropriate amount.
1439 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1440</div>
1441
1442<!-------------------------------------------------------------------------- -->
1443<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1444 <a name="loop-rotate">-loop-rotate: Rotate Loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1445</div>
1446<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1447 <p>A simple loop rotation transformation.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1448</div>
1449
1450<!-------------------------------------------------------------------------- -->
1451<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1452 <a name="loop-unroll">-loop-unroll: Unroll loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1453</div>
1454<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1455 <p>
1456 This pass implements a simple loop unroller. It works best when loops have
1457 been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
1458 allowing it to determine the trip counts of loops easily.
1459 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1460</div>
1461
1462<!-------------------------------------------------------------------------- -->
1463<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1464 <a name="loop-unswitch">-loop-unswitch: Unswitch loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1465</div>
1466<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1467 <p>
1468 This pass transforms loops that contain branches on loop-invariant conditions
1469 to have multiple loops. For example, it turns the left into the right code:
1470 </p>
1471
1472 <pre
1473>for (...) if (lic)
1474 A for (...)
1475 if (lic) A; B; C
1476 B else
1477 C for (...)
1478 A; C</pre>
1479
1480 <p>
1481 This can increase the size of the code exponentially (doubling it every time
1482 a loop is unswitched) so we only unswitch if the resultant code will be
1483 smaller than a threshold.
1484 </p>
1485
1486 <p>
1487 This pass expects LICM to be run before it to hoist invariant conditions out
1488 of the loop, to make the unswitching opportunity obvious.
1489 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1490</div>
1491
1492<!-------------------------------------------------------------------------- -->
1493<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1494 <a name="loopsimplify">-loopsimplify: Canonicalize natural loops</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1495</div>
1496<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1497 <p>
1498 This pass performs several transformations to transform natural loops into a
1499 simpler form, which makes subsequent analyses and transformations simpler and
1500 more effective.
1501 </p>
1502
1503 <p>
1504 Loop pre-header insertion guarantees that there is a single, non-critical
1505 entry edge from outside of the loop to the loop header. This simplifies a
1506 number of analyses and transformations, such as LICM.
1507 </p>
1508
1509 <p>
1510 Loop exit-block insertion guarantees that all exit blocks from the loop
1511 (blocks which are outside of the loop that have predecessors inside of the
1512 loop) only have predecessors from inside of the loop (and are thus dominated
1513 by the loop header). This simplifies transformations such as store-sinking
1514 that are built into LICM.
1515 </p>
1516
1517 <p>
1518 This pass also guarantees that loops will have exactly one backedge.
1519 </p>
1520
1521 <p>
1522 Note that the simplifycfg pass will clean up blocks which are split out but
1523 end up being unnecessary, so usage of this pass should not pessimize
1524 generated code.
1525 </p>
1526
1527 <p>
1528 This pass obviously modifies the CFG, but updates loop information and
1529 dominator information.
1530 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1531</div>
1532
1533<!-------------------------------------------------------------------------- -->
1534<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1535 <a name="lowerallocs">-lowerallocs: Lower allocations from instructions to calls</a>
1536</div>
1537<div class="doc_text">
1538 <p>
1539 Turn <tt>malloc</tt> and <tt>free</tt> instructions into <tt>@malloc</tt> and
1540 <tt>@free</tt> calls.
1541 </p>
1542
1543 <p>
1544 This is a target-dependent tranformation because it depends on the size of
1545 data types and alignment constraints.
1546 </p>
1547</div>
1548
1549<!-------------------------------------------------------------------------- -->
1550<div class="doc_subsection">
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1551 <a name="loweratomic">-loweratomic: Lower atomic intrinsics</a>
Peter Collingbourne3bababf2010-08-03 16:19:16 +0000[diff] [blame]1552</div>
1553<div class="doc_text">
1554 <p>
1555 This pass lowers atomic intrinsics to non-atomic form for use in a known
1556 non-preemptible environment.
1557 </p>
1558
1559 <p>
1560 The pass does not verify that the environment is non-preemptible (in
1561 general this would require knowledge of the entire call graph of the
1562 program including any libraries which may not be available in bitcode form);
1563 it simply lowers every atomic intrinsic.
1564 </p>
1565</div>
1566
1567<!-------------------------------------------------------------------------- -->
1568<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1569 <a name="lowerinvoke">-lowerinvoke: Lower invoke and unwind, for unwindless code generators</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1570</div>
1571<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1572 <p>
1573 This transformation is designed for use by code generators which do not yet
1574 support stack unwinding. This pass supports two models of exception handling
1575 lowering, the 'cheap' support and the 'expensive' support.
1576 </p>
1577
1578 <p>
1579 'Cheap' exception handling support gives the program the ability to execute
1580 any program which does not "throw an exception", by turning 'invoke'
1581 instructions into calls and by turning 'unwind' instructions into calls to
1582 abort(). If the program does dynamically use the unwind instruction, the
1583 program will print a message then abort.
1584 </p>
1585
1586 <p>
1587 'Expensive' exception handling support gives the full exception handling
1588 support to the program at the cost of making the 'invoke' instruction
1589 really expensive. It basically inserts setjmp/longjmp calls to emulate the
1590 exception handling as necessary.
1591 </p>
1592
1593 <p>
1594 Because the 'expensive' support slows down programs a lot, and EH is only
1595 used for a subset of the programs, it must be specifically enabled by the
1596 <tt>-enable-correct-eh-support</tt> option.
1597 </p>
1598
1599 <p>
1600 Note that after this pass runs the CFG is not entirely accurate (exceptional
1601 control flow edges are not correct anymore) so only very simple things should
1602 be done after the lowerinvoke pass has run (like generation of native code).
1603 This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
1604 support the invoke instruction yet" lowering pass.
1605 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1606</div>
1607
1608<!-------------------------------------------------------------------------- -->
1609<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1610 <a name="lowersetjmp">-lowersetjmp: Lower Set Jump</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1611</div>
1612<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1613 <p>
1614 Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
1615 instructions as necessary.
1616 </p>
1617
1618 <p>
1619 Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
1620 call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
1621 This unwinds the stack for us calling all of the destructors for
1622 objects allocated on the stack.
1623 </p>
1624
1625 <p>
1626 At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
1627 removed. The calls in a function that have a <tt>setjmp</tt> are converted to
1628 invoke where the except part checks to see if it's a <tt>longjmp</tt>
1629 exception and, if so, if it's handled in the function. If it is, then it gets
1630 the value returned by the <tt>longjmp</tt> and goes to where the basic block
1631 was split. <tt>invoke</tt> instructions are handled in a similar fashion with
1632 the original except block being executed if it isn't a <tt>longjmp</tt>
1633 except that is handled by that function.
1634 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1635</div>
1636
1637<!-------------------------------------------------------------------------- -->
1638<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1639 <a name="lowerswitch">-lowerswitch: Lower SwitchInst's to branches</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1640</div>
1641<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1642 <p>
1643 Rewrites <tt>switch</tt> instructions with a sequence of branches, which
1644 allows targets to get away with not implementing the switch instruction until
1645 it is convenient.
1646 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1647</div>
1648
1649<!-------------------------------------------------------------------------- -->
1650<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1651 <a name="mem2reg">-mem2reg: Promote Memory to Register</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1652</div>
1653<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1654 <p>
1655 This file promotes memory references to be register references. It promotes
1656 <tt>alloca</tt> instructions which only have <tt>load</tt>s and
1657 <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
1658 frontiers to place <tt>phi</tt> nodes, then traversing the function in
1659 depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
1660 appropriate. This is just the standard SSA construction algorithm to construct
1661 "pruned" SSA form.
1662 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1663</div>
1664
1665<!-------------------------------------------------------------------------- -->
1666<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1667 <a name="memcpyopt">-memcpyopt: Optimize use of memcpy and friend</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1668</div>
1669<div class="doc_text">
1670 <p>
1671 This pass performs various transformations related to eliminating memcpy
1672 calls, or transforming sets of stores into memset's.
1673 </p>
1674</div>
1675
1676<!-------------------------------------------------------------------------- -->
1677<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1678 <a name="mergefunc">-mergefunc: Merge Functions</a>
1679</div>
1680<div class="doc_text">
1681 <p>This pass looks for equivalent functions that are mergable and folds them.
1682
1683 A hash is computed from the function, based on its type and number of
1684 basic blocks.
1685
1686 Once all hashes are computed, we perform an expensive equality comparison
1687 on each function pair. This takes n^2/2 comparisons per bucket, so it's
1688 important that the hash function be high quality. The equality comparison
1689 iterates through each instruction in each basic block.
1690
1691 When a match is found the functions are folded. If both functions are
1692 overridable, we move the functionality into a new internal function and
1693 leave two overridable thunks to it.
1694 </p>
1695</div>
1696
1697<!-------------------------------------------------------------------------- -->
1698<div class="doc_subsection">
1699 <a name="mergereturn">-mergereturn: Unify function exit nodes</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1700</div>
1701<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1702 <p>
1703 Ensure that functions have at most one <tt>ret</tt> instruction in them.
1704 Additionally, it keeps track of which node is the new exit node of the CFG.
1705 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1706</div>
1707
1708<!-------------------------------------------------------------------------- -->
1709<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1710 <a name="partial-inliner">-partial-inliner: Partial Inliner</a>
1711</div>
1712<div class="doc_text">
1713 <p>This pass performs partial inlining, typically by inlining an if
1714 statement that surrounds the body of the function.
1715 </p>
1716</div>
1717
1718<!-------------------------------------------------------------------------- -->
1719<div class="doc_subsection">
1720 <a name="partialspecialization">-partialspecialization: Partial Specialization</a>
1721</div>
1722<div class="doc_text">
1723 <p>This pass finds function arguments that are often a common constant and
1724 specializes a version of the called function for that constant.
1725
1726 This pass simply does the cloning for functions it specializes. It depends
1727 on <a href="#ipsccp">IPSCCP</a> and <a href="#deadargelim">DAE</a> to clean up the results.
1728
1729 The initial heuristic favors constant arguments that are used in control
1730 flow.
1731 </p>
1732</div>
1733
1734<!-------------------------------------------------------------------------- -->
1735<div class="doc_subsection">
1736 <a name="prune-eh">-prune-eh: Remove unused exception handling info</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1737</div>
1738<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1739 <p>
1740 This file implements a simple interprocedural pass which walks the call-graph,
1741 turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
1742 only if the callee cannot throw an exception. It implements this as a
1743 bottom-up traversal of the call-graph.
1744 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1745</div>
1746
1747<!-------------------------------------------------------------------------- -->
1748<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1749 <a name="reassociate">-reassociate: Reassociate expressions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1750</div>
1751<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1752 <p>
1753 This pass reassociates commutative expressions in an order that is designed
1754 to promote better constant propagation, GCSE, LICM, PRE, etc.
1755 </p>
1756
1757 <p>
1758 For example: 4 + (<var>x</var> + 5) ⇒ <var>x</var> + (4 + 5)
1759 </p>
1760
1761 <p>
1762 In the implementation of this algorithm, constants are assigned rank = 0,
1763 function arguments are rank = 1, and other values are assigned ranks
1764 corresponding to the reverse post order traversal of current function
1765 (starting at 2), which effectively gives values in deep loops higher rank
1766 than values not in loops.
1767 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1768</div>
1769
1770<!-------------------------------------------------------------------------- -->
1771<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1772 <a name="reg2mem">-reg2mem: Demote all values to stack slots</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1773</div>
1774<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1775 <p>
1776 This file demotes all registers to memory references. It is intented to be
1777 the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]1778 <tt>load</tt> instructions, the only values live across basic blocks are
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1779 <tt>alloca</tt> instructions and <tt>load</tt> instructions before
1780 <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
1781 easier. To make later hacking easier, the entry block is split into two, such
1782 that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
1783 entry block.
1784 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1785</div>
1786
1787<!-------------------------------------------------------------------------- -->
1788<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1789 <a name="scalarrepl">-scalarrepl: Scalar Replacement of Aggregates</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1790</div>
1791<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1792 <p>
1793 The well-known scalar replacement of aggregates transformation. This
1794 transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
1795 or array) into individual <tt>alloca</tt> instructions for each member if
1796 possible. Then, if possible, it transforms the individual <tt>alloca</tt>
1797 instructions into nice clean scalar SSA form.
1798 </p>
1799
1800 <p>
1801 This combines a simple scalar replacement of aggregates algorithm with the <a
1802 href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
1803 especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
1804 then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
1805 promote works well.
1806 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1807</div>
1808
1809<!-------------------------------------------------------------------------- -->
1810<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1811 <a name="sccp">-sccp: Sparse Conditional Constant Propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1812</div>
1813<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1814 <p>
1815 Sparse conditional constant propagation and merging, which can be summarized
1816 as:
1817 </p>
1818
1819 <ol>
1820 <li>Assumes values are constant unless proven otherwise</li>
1821 <li>Assumes BasicBlocks are dead unless proven otherwise</li>
1822 <li>Proves values to be constant, and replaces them with constants</li>
1823 <li>Proves conditional branches to be unconditional</li>
1824 </ol>
1825
1826 <p>
1827 Note that this pass has a habit of making definitions be dead. It is a good
1828 idea to to run a DCE pass sometime after running this pass.
1829 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1830</div>
1831
1832<!-------------------------------------------------------------------------- -->
1833<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1834 <a name="sink">-sink: Code Sinking</a>
1835</div>
1836<div class="doc_text">
1837 <p>This pass moves instructions into successor blocks, when possible, so that
1838 they aren't executed on paths where their results aren't needed.
1839 </p>
1840</div>
1841
1842<!-------------------------------------------------------------------------- -->
1843<div class="doc_subsection">
1844 <a name="simplify-libcalls">-simplify-libcalls: Simplify well-known library calls</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1845</div>
1846<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1847 <p>
1848 Applies a variety of small optimizations for calls to specific well-known
1849 function calls (e.g. runtime library functions). For example, a call
1850 <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
1851 transformed into simply <tt>return 3</tt>.
1852 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1853</div>
1854
1855<!-------------------------------------------------------------------------- -->
1856<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1857 <a name="simplify-libcalls-halfpowr">-simplify-libcalls-halfpowr: Simplify half_powr library calls</a>
1858</div>
1859<div class="doc_text">
1860 <p>Simple pass that applies an experimental transformation on calls
1861 to specific functions.
1862 </p>
1863</div>
1864
1865<!-------------------------------------------------------------------------- -->
1866<div class="doc_subsection">
1867 <a name="simplifycfg">-simplifycfg: Simplify the CFG</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1868</div>
1869<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1870 <p>
1871 Performs dead code elimination and basic block merging. Specifically:
1872 </p>
1873
1874 <ol>
1875 <li>Removes basic blocks with no predecessors.</li>
1876 <li>Merges a basic block into its predecessor if there is only one and the
1877 predecessor only has one successor.</li>
1878 <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
1879 <li>Eliminates a basic block that only contains an unconditional
1880 branch.</li>
1881 </ol>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1882</div>
1883
1884<!-------------------------------------------------------------------------- -->
1885<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1886 <a name="split-geps">-split-geps: Split complex GEPs into simple GEPs</a>
1887</div>
1888<div class="doc_text">
1889 <p>This function breaks GEPs with more than 2 non-zero operands into smaller
1890 GEPs each with no more than 2 non-zero operands. This exposes redundancy
1891 between GEPs with common initial operand sequences.
1892 </p>
1893</div>
1894
1895<!-------------------------------------------------------------------------- -->
1896<div class="doc_subsection">
1897 <a name="ssi">-ssi: Static Single Information Construction</a>
1898</div>
1899<div class="doc_text">
1900 <p>This pass converts a list of variables to the Static Single Information
1901 form.
1902
1903 We are building an on-demand representation, that is, we do not convert
1904 every single variable in the target function to SSI form. Rather, we receive
1905 a list of target variables that must be converted. We also do not
1906 completely convert a target variable to the SSI format. Instead, we only
1907 change the variable in the points where new information can be attached
1908 to its live range, that is, at branch points.
1909 </p>
1910</div>
1911
1912<!-------------------------------------------------------------------------- -->
1913<div class="doc_subsection">
1914 <a name="ssi-everything">-ssi-everything: Static Single Information Construction (everything, intended for debugging)</a>
1915</div>
1916<div class="doc_text">
1917 <p>A pass that runs <a href="#ssi">SSI</a> on every non-void variable, intended for debugging.
1918 </p>
1919</div>
1920
1921<!-------------------------------------------------------------------------- -->
1922<div class="doc_subsection">
1923 <a name="strip">-strip: Strip all symbols from a module</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1924</div>
1925<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1926 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1927 performs code stripping. this transformation can delete:
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1928 </p>
1929
1930 <ol>
1931 <li>names for virtual registers</li>
1932 <li>symbols for internal globals and functions</li>
1933 <li>debug information</li>
1934 </ol>
1935
1936 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1937 note that this transformation makes code much less readable, so it should
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1938 only be used in situations where the <tt>strip</tt> utility would be used,
1939 such as reducing code size or making it harder to reverse engineer code.
1940 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1941</div>
1942
1943<!-------------------------------------------------------------------------- -->
1944<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1945 <a name="strip-dead-prototypes">-strip-dead-prototypes: Remove unused function declarations</a>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1946</div>
1947<div class="doc_text">
1948 <p>
1949 This pass loops over all of the functions in the input module, looking for
1950 dead declarations and removes them. Dead declarations are declarations of
1951 functions for which no implementation is available (i.e., declarations for
1952 unused library functions).
1953 </p>
1954</div>
1955
1956<!-------------------------------------------------------------------------- -->
1957<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1958 <a name="strip-debug-declare">-strip-debug-declare: Strip all llvm.dbg.declare intrinsics</a>
1959</div>
1960<div class="doc_text">
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1961 <p>This pass implements code stripping. Specifically, it can delete:</p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1962 <ul>
1963 <li>names for virtual registers</li>
1964 <li>symbols for internal globals and functions</li>
1965 <li>debug information</li>
1966 </ul>
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1967 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1968 Note that this transformation makes code much less readable, so it should
1969 only be used in situations where the 'strip' utility would be used, such as
1970 reducing code size or making it harder to reverse engineer code.
1971 </p>
1972</div>
1973
1974<!-------------------------------------------------------------------------- -->
1975<div class="doc_subsection">
1976 <a name="strip-nondebug">-strip-nondebug: Strip all symbols, except dbg symbols, from a module</a>
1977</div>
1978<div class="doc_text">
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1979 <p>This pass implements code stripping. Specifically, it can delete:</p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]1980 <ul>
1981 <li>names for virtual registers</li>
1982 <li>symbols for internal globals and functions</li>
1983 <li>debug information</li>
1984 </ul>
Peter Collingbournec3086ba2010-08-06 02:13:25 +0000[diff] [blame]1985 <p>
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]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 Henriksena8a118b2008-05-08 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2017 <a name="tailcallelim">-tailcallelim: Tail Call Elimination</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2018</div>
2019<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2045</div>
2046
2047<!-------------------------------------------------------------------------- -->
2048<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2049 <a name="tailduplicate">-tailduplicate: Tail Duplication</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2050</div>
2051<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 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>
Reid Spencerd9aac122007-03-26 09:32:31 +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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2069 <a name="deadarghaX0r">-deadarghaX0r: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2070</div>
2071<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2076</div>
2077
2078<!-------------------------------------------------------------------------- -->
2079<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2080 <a name="extract-blocks">-extract-blocks: Extract Basic Blocks From Module (for bugpoint use)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2081</div>
2082<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2086</div>
2087
2088<!-------------------------------------------------------------------------- -->
2089<div class="doc_subsection">
Duncan Sands5c603862010-07-06 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2103</div>
2104<div class="doc_text">
Gordon Henriksen90a52142007-11-05 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2114</div>
2115
2116<!-------------------------------------------------------------------------- -->
2117<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2118 <a name="verify">-verify: Module Verifier</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2119</div>
2120<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 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 Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]2129 <ul>
Gordon Henriksen75ff18e2007-11-04 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 Lattner46b3abc2009-10-28 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 Lewycky0c78ac12008-03-28 06:46:51 +0000[diff] [blame]2140 <li>Only phi nodes can be self referential: <tt>%x = add i32 %x, %x</tt> is
Gordon Henriksen873390e2007-11-04 18:17:58 +0000[diff] [blame]2141 invalid.</li>
Gordon Henriksen75ff18e2007-11-04 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 Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]2159 </ul>
Gordon Henriksen75ff18e2007-11-04 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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2165</div>
2166
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2167<!-------------------------------------------------------------------------- -->
2168<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2169 <a name="view-cfg">-view-cfg: View CFG of function</a>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2170</div>
2171<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]2172 <p>
2173 Displays the control flow graph using the GraphViz tool.
2174 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2175</div>
2176
2177<!-------------------------------------------------------------------------- -->
2178<div class="doc_subsection">
Duncan Sands5c603862010-07-06 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 Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2180</div>
2181<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 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 Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]2186</div>
2187
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]2188<!-------------------------------------------------------------------------- -->
2189<div class="doc_subsection">
Duncan Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2190 <a name="view-dom">-view-dom: View dominator tree of function</a>
Tobias Grosser733783b2010-05-07 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2200 <a name="view-dom-only">-view-dom-only: View dominator tree of function (with no function
Tobias Grosser733783b2010-05-07 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2213 <a name="view-postdom">-view-postdom: View post dominator tree of function</a>
Tobias Grosser733783b2010-05-07 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 Sands5c603862010-07-06 15:52:15 +0000[diff] [blame]2223 <a name="view-postdom-only">-view-postdom-only: View post dominator tree of function (with no
Tobias Grosser733783b2010-05-07 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
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2234<!-- *********************************************************************** -->
2235
2236<hr>
2237<address>
2238 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]2239 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]2240 <a href="http://validator.w3.org/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]2241 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]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>