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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / e5ff9ef195722cbbf4b6ed7d34412f7277d05eda / . / 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"
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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>$2</td></tr>\n";
30 push @y, "$o <a name=\"$1\">$2</a>\n";
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>
94<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]95<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Construction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]96<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]97<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
98<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
99<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]100<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]101<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]102<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
103<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
104<tr><td><a href="#print-cfg-sccs">-print-cfg-sccs</a></td><td>Print SCCs of each function CFG</td></tr>
105<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
106<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
107<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
108<tr><td><a href="#print-used-types">-print-used-types</a></td><td>Find Used Types</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]109<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
110<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
111<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
112
113
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]114<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
115<tr><th>Option</th><th>Name</th></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]116<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
117<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
118<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]119<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]120<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]121<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
122<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
123<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
124<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
125<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
126<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
127<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]128<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
129<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]130<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]131<tr><td><a href="#indmemrem">-indmemrem</a></td><td>Indirect Malloc and Free Removal</td></tr>
132<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
133<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
134<tr><td><a href="#insert-block-profiling">-insert-block-profiling</a></td><td>Insert instrumentation for block profiling</td></tr>
135<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
136<tr><td><a href="#insert-function-profiling">-insert-function-profiling</a></td><td>Insert instrumentation for function profiling</td></tr>
137<tr><td><a href="#insert-null-profiling-rs">-insert-null-profiling-rs</a></td><td>Measure profiling framework overhead</td></tr>
138<tr><td><a href="#insert-rs-profiling-framework">-insert-rs-profiling-framework</a></td><td>Insert random sampling instrumentation framework</td></tr>
139<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
140<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
141<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
142<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]143<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]144<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
145<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]146<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]147<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
148<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]149<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]150<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]151<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
152<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
153<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
154<tr><td><a href="#loopsimplify">-loopsimplify</a></td><td>Canonicalize natural loops</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]155<tr><td><a href="#lowerallocs">-lowerallocs</a></td><td>Lower allocations from instructions to calls</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]156<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]157<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
158<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
159<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]160<tr><td><a href="#memcpyopt">-memcpyopt</a></td><td>Optimize use of memcpy and friends</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]161<tr><td><a href="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]162<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]163<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
164<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]165<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates</td></tr>
166<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
167<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
168<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
169<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]170<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Remove unused function declarations</td></tr>
171<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]172<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
173<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]174
175
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]176<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
177<tr><th>Option</th><th>Name</th></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]178<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
179<tr><td><a href="#extract-blocks">-extract-blocks</a></td><td>Extract Basic Blocks From Module (for bugpoint use)</td></tr>
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]180<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]181<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]182<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
183<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]184<tr><td><a href="#view-dom">-view-dom</a></td><td>View dominator tree of function</td></tr>
185<tr><td><a href="#view-dom-only">-view-dom-only</a></td><td>View dominator tree of function (with no function bodies)</td></tr>
186<tr><td><a href="#view-postdom">-view-postdom</a></td><td>View post dominator tree of function</td></tr>
187<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]188</table>
189</div>
190
191<!-- ======================================================================= -->
192<div class="doc_section"> <a name="example">Analysis Passes</a></div>
193<div class="doc_text">
194 <p>This section describes the LLVM Analysis Passes.</p>
195</div>
196
197<!-------------------------------------------------------------------------- -->
198<div class="doc_subsection">
199 <a name="aa-eval">Exhaustive Alias Analysis Precision Evaluator</a>
200</div>
201<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]202 <p>This is a simple N^2 alias analysis accuracy evaluator.
203 Basically, for each function in the program, it simply queries to see how the
204 alias analysis implementation answers alias queries between each pair of
205 pointers in the function.</p>
206
207 <p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
208 Spadini, and Wojciech Stryjewski.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]209</div>
210
211<!-------------------------------------------------------------------------- -->
212<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]213 <a name="basicaa">Basic Alias Analysis (default AA impl)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]214</div>
215<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]216 <p>
217 This is the default implementation of the Alias Analysis interface
218 that simply implements a few identities (two different globals cannot alias,
219 etc), but otherwise does no analysis.
220 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]221</div>
222
223<!-------------------------------------------------------------------------- -->
224<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]225 <a name="basiccg">Basic CallGraph Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]226</div>
227<div class="doc_text">
228 <p>Yet to be written.</p>
229</div>
230
231<!-------------------------------------------------------------------------- -->
232<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]233 <a name="codegenprepare">Optimize for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]234</div>
235<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]236 <p>
237 This pass munges the code in the input function to better prepare it for
238 SelectionDAG-based code generation. This works around limitations in it's
239 basic-block-at-a-time approach. It should eventually be removed.
240 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]241</div>
242
243<!-------------------------------------------------------------------------- -->
244<div class="doc_subsection">
245 <a name="count-aa">Count Alias Analysis Query Responses</a>
246</div>
247<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]248 <p>
249 A pass which can be used to count how many alias queries
250 are being made and how the alias analysis implementation being used responds.
251 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]252</div>
253
254<!-------------------------------------------------------------------------- -->
255<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]256 <a name="debug-aa">AA use debugger</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]257</div>
258<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]259 <p>
260 This simple pass checks alias analysis users to ensure that if they
261 create a new value, they do not query AA without informing it of the value.
262 It acts as a shim over any other AA pass you want.
263 </p>
264
265 <p>
266 Yes keeping track of every value in the program is expensive, but this is
267 a debugging pass.
268 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]269</div>
270
271<!-------------------------------------------------------------------------- -->
272<div class="doc_subsection">
273 <a name="domfrontier">Dominance Frontier Construction</a>
274</div>
275<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]276 <p>
277 This pass is a simple dominator construction algorithm for finding forward
278 dominator frontiers.
279 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]280</div>
281
282<!-------------------------------------------------------------------------- -->
283<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]284 <a name="domtree">Dominator Tree Construction</a>
285</div>
286<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]287 <p>
288 This pass is a simple dominator construction algorithm for finding forward
289 dominators.
290 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]291</div>
292
293<!-------------------------------------------------------------------------- -->
294<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]295 <a name="dot-callgraph">Print Call Graph to 'dot' file</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]296</div>
297<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]298 <p>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]299 This pass, only available in <code>opt</code>, prints the call graph into a
300 <code>.dot</code> graph. This graph can then be processed with the "dot" tool
301 to convert it to postscript or some other suitable format.
302 </p>
303</div>
304
305<!-------------------------------------------------------------------------- -->
306<div class="doc_subsection">
307 <a name="dot-cfg">Print CFG of function to 'dot' file</a>
308</div>
309<div class="doc_text">
310 <p>
311 This pass, only available in <code>opt</code>, prints the control flow graph
312 into a <code>.dot</code> graph. This graph can then be processed with the
313 "dot" tool to convert it to postscript or some other suitable format.
314 </p>
315</div>
316
317<!-------------------------------------------------------------------------- -->
318<div class="doc_subsection">
319 <a name="dot-cfg-only">Print CFG of function to 'dot' file (with no function bodies)</a>
320</div>
321<div class="doc_text">
322 <p>
323 This pass, only available in <code>opt</code>, prints the control flow graph
324 into a <code>.dot</code> graph, omitting the function bodies. This graph can
325 then be processed with the "dot" tool to convert it to postscript or some
326 other suitable format.
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]327 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]328</div>
329
330<!-------------------------------------------------------------------------- -->
331<div class="doc_subsection">
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]332 <a name="dot-dom">Print dominator tree of function to 'dot' file</a>
333</div>
334<div class="doc_text">
335 <p>
336 This pass, only available in <code>opt</code>, prints the dominator tree
337 into a <code>.dot</code> graph. This graph can then be processed with the
338 "dot" tool to convert it to postscript or some other suitable format.
339 </p>
340</div>
341
342<!-------------------------------------------------------------------------- -->
343<div class="doc_subsection">
344 <a name="dot-dom-only">Print dominator tree of function to 'dot' file (with no
345 function bodies)</a>
346</div>
347<div class="doc_text">
348 <p>
349 This pass, only available in <code>opt</code>, prints the dominator tree
350 into a <code>.dot</code> graph, omitting the function bodies. This graph can
351 then be processed with the "dot" tool to convert it to postscript or some
352 other suitable format.
353 </p>
354</div>
355
356<!-------------------------------------------------------------------------- -->
357<div class="doc_subsection">
358 <a name="dot-postdom">Print post dominator tree of function to 'dot' file</a>
359</div>
360<div class="doc_text">
361 <p>
362 This pass, only available in <code>opt</code>, prints the post dominator tree
363 into a <code>.dot</code> graph. This graph can then be processed with the
364 "dot" tool to convert it to postscript or some other suitable format.
365 </p>
366</div>
367
368<!-------------------------------------------------------------------------- -->
369<div class="doc_subsection">
370 <a name="dot-postdom-only">Print post dominator tree of function to 'dot' file
371 (with no function bodies)</a>
372</div>
373<div class="doc_text">
374 <p>
375 This pass, only available in <code>opt</code>, prints the post dominator tree
376 into a <code>.dot</code> graph, omitting the function bodies. This graph can
377 then be processed with the "dot" tool to convert it to postscript or some
378 other suitable format.
379 </p>
380</div>
381
382<!-------------------------------------------------------------------------- -->
383<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]384 <a name="globalsmodref-aa">Simple mod/ref analysis for globals</a>
385</div>
386<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]387 <p>
388 This simple pass provides alias and mod/ref information for global values
389 that do not have their address taken, and keeps track of whether functions
390 read or write memory (are "pure"). For this simple (but very common) case,
391 we can provide pretty accurate and useful information.
392 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]393</div>
394
395<!-------------------------------------------------------------------------- -->
396<div class="doc_subsection">
397 <a name="instcount">Counts the various types of Instructions</a>
398</div>
399<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]400 <p>
401 This pass collects the count of all instructions and reports them
402 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]403</div>
404
405<!-------------------------------------------------------------------------- -->
406<div class="doc_subsection">
407 <a name="intervals">Interval Partition Construction</a>
408</div>
409<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]410 <p>
411 This analysis calculates and represents the interval partition of a function,
412 or a preexisting interval partition.
413 </p>
414
415 <p>
416 In this way, the interval partition may be used to reduce a flow graph down
417 to its degenerate single node interval partition (unless it is irreducible).
418 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]419</div>
420
421<!-------------------------------------------------------------------------- -->
422<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]423 <a name="loops">Natural Loop Construction</a>
424</div>
425<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]426 <p>
427 This analysis is used to identify natural loops and determine the loop depth
428 of various nodes of the CFG. Note that the loops identified may actually be
429 several natural loops that share the same header node... not just a single
430 natural loop.
431 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]432</div>
433
434<!-------------------------------------------------------------------------- -->
435<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]436 <a name="memdep">Memory Dependence Analysis</a>
437</div>
438<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]439 <p>
440 An analysis that determines, for a given memory operation, what preceding
441 memory operations it depends on. It builds on alias analysis information, and
442 tries to provide a lazy, caching interface to a common kind of alias
443 information query.
444 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]445</div>
446
447<!-------------------------------------------------------------------------- -->
448<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]449 <a name="no-aa">No Alias Analysis (always returns 'may' alias)</a>
450</div>
451<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]452 <p>
453 Always returns "I don't know" for alias queries. NoAA is unlike other alias
454 analysis implementations, in that it does not chain to a previous analysis. As
455 such it doesn't follow many of the rules that other alias analyses must.
456 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]457</div>
458
459<!-------------------------------------------------------------------------- -->
460<div class="doc_subsection">
461 <a name="no-profile">No Profile Information</a>
462</div>
463<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]464 <p>
465 The default "no profile" implementation of the abstract
466 <code>ProfileInfo</code> interface.
467 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]468</div>
469
470<!-------------------------------------------------------------------------- -->
471<div class="doc_subsection">
472 <a name="postdomfrontier">Post-Dominance Frontier Construction</a>
473</div>
474<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]475 <p>
476 This pass is a simple post-dominator construction algorithm for finding
477 post-dominator frontiers.
478 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]479</div>
480
481<!-------------------------------------------------------------------------- -->
482<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]483 <a name="postdomtree">Post-Dominator Tree Construction</a>
484</div>
485<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]486 <p>
487 This pass is a simple post-dominator construction algorithm for finding
488 post-dominators.
489 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]490</div>
491
492<!-------------------------------------------------------------------------- -->
493<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]494 <a name="print-alias-sets">Alias Set Printer</a>
495</div>
496<div class="doc_text">
497 <p>Yet to be written.</p>
498</div>
499
500<!-------------------------------------------------------------------------- -->
501<div class="doc_subsection">
502 <a name="print-callgraph">Print a call graph</a>
503</div>
504<div class="doc_text">
505 <p>
506 This pass, only available in <code>opt</code>, prints the call graph to
507 standard output in a human-readable form.
508 </p>
509</div>
510
511<!-------------------------------------------------------------------------- -->
512<div class="doc_subsection">
513 <a name="print-callgraph-sccs">Print SCCs of the Call Graph</a>
514</div>
515<div class="doc_text">
516 <p>
517 This pass, only available in <code>opt</code>, prints the SCCs of the call
518 graph to standard output in a human-readable form.
519 </p>
520</div>
521
522<!-------------------------------------------------------------------------- -->
523<div class="doc_subsection">
524 <a name="print-cfg-sccs">Print SCCs of each function CFG</a>
525</div>
526<div class="doc_text">
527 <p>
528 This pass, only available in <code>opt</code>, prints the SCCs of each
529 function CFG to standard output in a human-readable form.
530 </p>
531</div>
532
533<!-------------------------------------------------------------------------- -->
534<div class="doc_subsection">
535 <a name="print-externalfnconstants">Print external fn callsites passed constants</a>
536</div>
537<div class="doc_text">
538 <p>
539 This pass, only available in <code>opt</code>, prints out call sites to
540 external functions that are called with constant arguments. This can be
541 useful when looking for standard library functions we should constant fold
542 or handle in alias analyses.
543 </p>
544</div>
545
546<!-------------------------------------------------------------------------- -->
547<div class="doc_subsection">
548 <a name="print-function">Print function to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]549</div>
550<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]551 <p>
552 The <code>PrintFunctionPass</code> class is designed to be pipelined with
553 other <code>FunctionPass</code>es, and prints out the functions of the module
554 as they are processed.
555 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]556</div>
557
558<!-------------------------------------------------------------------------- -->
559<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]560 <a name="print-module">Print module to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]561</div>
562<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]563 <p>
564 This pass simply prints out the entire module when it is executed.
565 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]566</div>
567
568<!-------------------------------------------------------------------------- -->
569<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]570 <a name="print-used-types">Find Used Types</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]571</div>
572<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]573 <p>
574 This pass is used to seek out all of the types in use by the program. Note
575 that this analysis explicitly does not include types only used by the symbol
576 table.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]577</div>
578
579<!-------------------------------------------------------------------------- -->
580<div class="doc_subsection">
581 <a name="profile-loader">Load profile information from llvmprof.out</a>
582</div>
583<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]584 <p>
585 A concrete implementation of profiling information that loads the information
586 from a profile dump file.
587 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]588</div>
589
590<!-------------------------------------------------------------------------- -->
591<div class="doc_subsection">
592 <a name="scalar-evolution">Scalar Evolution Analysis</a>
593</div>
594<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]595 <p>
596 The <code>ScalarEvolution</code> analysis can be used to analyze and
597 catagorize scalar expressions in loops. It specializes in recognizing general
598 induction variables, representing them with the abstract and opaque
599 <code>SCEV</code> class. Given this analysis, trip counts of loops and other
600 important properties can be obtained.
601 </p>
602
603 <p>
604 This analysis is primarily useful for induction variable substitution and
605 strength reduction.
606 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]607</div>
608
609<!-------------------------------------------------------------------------- -->
610<div class="doc_subsection">
611 <a name="targetdata">Target Data Layout</a>
612</div>
613<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]614 <p>Provides other passes access to information on how the size and alignment
615 required by the the target ABI for various data types.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]616</div>
617
618<!-- ======================================================================= -->
619<div class="doc_section"> <a name="transform">Transform Passes</a></div>
620<div class="doc_text">
621 <p>This section describes the LLVM Transform Passes.</p>
622</div>
623
624<!-------------------------------------------------------------------------- -->
625<div class="doc_subsection">
626 <a name="adce">Aggressive Dead Code Elimination</a>
627</div>
628<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]629 <p>ADCE aggressively tries to eliminate code. This pass is similar to
630 <a href="#dce">DCE</a> but it assumes that values are dead until proven
631 otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
632 the liveness of values.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]633</div>
634
635<!-------------------------------------------------------------------------- -->
636<div class="doc_subsection">
637 <a name="argpromotion">Promote 'by reference' arguments to scalars</a>
638</div>
639<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]640 <p>
641 This pass promotes "by reference" arguments to be "by value" arguments. In
642 practice, this means looking for internal functions that have pointer
643 arguments. If it can prove, through the use of alias analysis, that an
644 argument is *only* loaded, then it can pass the value into the function
645 instead of the address of the value. This can cause recursive simplification
646 of code and lead to the elimination of allocas (especially in C++ template
647 code like the STL).
648 </p>
649
650 <p>
651 This pass also handles aggregate arguments that are passed into a function,
652 scalarizing them if the elements of the aggregate are only loaded. Note that
653 it refuses to scalarize aggregates which would require passing in more than
654 three operands to the function, because passing thousands of operands for a
655 large array or structure is unprofitable!
656 </p>
657
658 <p>
659 Note that this transformation could also be done for arguments that are only
660 stored to (returning the value instead), but does not currently. This case
661 would be best handled when and if LLVM starts supporting multiple return
662 values from functions.
663 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]664</div>
665
666<!-------------------------------------------------------------------------- -->
667<div class="doc_subsection">
668 <a name="block-placement">Profile Guided Basic Block Placement</a>
669</div>
670<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]671 <p>This pass is a very simple profile guided basic block placement algorithm.
672 The idea is to put frequently executed blocks together at the start of the
673 function and hopefully increase the number of fall-through conditional
674 branches. If there is no profile information for a particular function, this
675 pass basically orders blocks in depth-first order.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]676</div>
677
678<!-------------------------------------------------------------------------- -->
679<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]680 <a name="break-crit-edges">Break critical edges in CFG</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]681</div>
682<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]683 <p>
684 Break all of the critical edges in the CFG by inserting a dummy basic block.
685 It may be "required" by passes that cannot deal with critical edges. This
686 transformation obviously invalidates the CFG, but can update forward dominator
687 (set, immediate dominators, tree, and frontier) information.
688 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]689</div>
690
691<!-------------------------------------------------------------------------- -->
692<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]693 <a name="codegenprepare">Prepare a function for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]694</div>
695<div class="doc_text">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]696 This pass munges the code in the input function to better prepare it for
697 SelectionDAG-based code generation. This works around limitations in it's
698 basic-block-at-a-time approach. It should eventually be removed.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]699</div>
700
701<!-------------------------------------------------------------------------- -->
702<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]703 <a name="constmerge">Merge Duplicate Global Constants</a>
704</div>
705<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]706 <p>
707 Merges duplicate global constants together into a single constant that is
708 shared. This is useful because some passes (ie TraceValues) insert a lot of
709 string constants into the program, regardless of whether or not an existing
710 string is available.
711 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]712</div>
713
714<!-------------------------------------------------------------------------- -->
715<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]716 <a name="constprop">Simple constant propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]717</div>
718<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]719 <p>This file implements constant propagation and merging. It looks for
720 instructions involving only constant operands and replaces them with a
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]721 constant value instead of an instruction. For example:</p>
722 <blockquote><pre>add i32 1, 2</pre></blockquote>
723 <p>becomes</p>
724 <blockquote><pre>i32 3</pre></blockquote>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]725 <p>NOTE: this pass has a habit of making definitions be dead. It is a good
726 idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
727 sometime after running this pass.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]728</div>
729
730<!-------------------------------------------------------------------------- -->
731<div class="doc_subsection">
732 <a name="dce">Dead Code Elimination</a>
733</div>
734<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]735 <p>
736 Dead code elimination is similar to <a href="#die">dead instruction
737 elimination</a>, but it rechecks instructions that were used by removed
738 instructions to see if they are newly dead.
739 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]740</div>
741
742<!-------------------------------------------------------------------------- -->
743<div class="doc_subsection">
744 <a name="deadargelim">Dead Argument Elimination</a>
745</div>
746<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]747 <p>
748 This pass deletes dead arguments from internal functions. Dead argument
749 elimination removes arguments which are directly dead, as well as arguments
750 only passed into function calls as dead arguments of other functions. This
751 pass also deletes dead arguments in a similar way.
752 </p>
753
754 <p>
755 This pass is often useful as a cleanup pass to run after aggressive
756 interprocedural passes, which add possibly-dead arguments.
757 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]758</div>
759
760<!-------------------------------------------------------------------------- -->
761<div class="doc_subsection">
762 <a name="deadtypeelim">Dead Type Elimination</a>
763</div>
764<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]765 <p>
766 This pass is used to cleanup the output of GCC. It eliminate names for types
767 that are unused in the entire translation unit, using the <a
768 href="#findusedtypes">find used types</a> pass.
769 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]770</div>
771
772<!-------------------------------------------------------------------------- -->
773<div class="doc_subsection">
774 <a name="die">Dead Instruction Elimination</a>
775</div>
776<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]777 <p>
778 Dead instruction elimination performs a single pass over the function,
779 removing instructions that are obviously dead.
780 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]781</div>
782
783<!-------------------------------------------------------------------------- -->
784<div class="doc_subsection">
785 <a name="dse">Dead Store Elimination</a>
786</div>
787<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]788 <p>
789 A trivial dead store elimination that only considers basic-block local
790 redundant stores.
791 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]792</div>
793
794<!-------------------------------------------------------------------------- -->
795<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]796 <a name="globaldce">Dead Global Elimination</a>
797</div>
798<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]799 <p>
800 This transform is designed to eliminate unreachable internal globals from the
801 program. It uses an aggressive algorithm, searching out globals that are
802 known to be alive. After it finds all of the globals which are needed, it
803 deletes whatever is left over. This allows it to delete recursive chunks of
804 the program which are unreachable.
805 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]806</div>
807
808<!-------------------------------------------------------------------------- -->
809<div class="doc_subsection">
810 <a name="globalopt">Global Variable Optimizer</a>
811</div>
812<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]813 <p>
814 This pass transforms simple global variables that never have their address
815 taken. If obviously true, it marks read/write globals as constant, deletes
816 variables only stored to, etc.
817 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]818</div>
819
820<!-------------------------------------------------------------------------- -->
821<div class="doc_subsection">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]822 <a name="gvn">Global Value Numbering</a>
823</div>
824<div class="doc_text">
825 <p>
Chris Lattner60f03402009-10-10 18:40:48 +0000[diff] [blame]826 This pass performs global value numbering to eliminate fully and partially
827 redundant instructions. It also performs redundant load elimination.
Matthijs Kooijman845f5242008-06-05 07:55:49 +0000[diff] [blame]828 </p>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]829</div>
830
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]831
832<!-------------------------------------------------------------------------- -->
833<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]834 <a name="indmemrem">Indirect Malloc and Free Removal</a>
835</div>
836<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]837 <p>
838 This pass finds places where memory allocation functions may escape into
839 indirect land. Some transforms are much easier (aka possible) only if free
840 or malloc are not called indirectly.
841 </p>
842
843 <p>
844 Thus find places where the address of memory functions are taken and construct
845 bounce functions with direct calls of those functions.
846 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]847</div>
848
849<!-------------------------------------------------------------------------- -->
850<div class="doc_subsection">
851 <a name="indvars">Canonicalize Induction Variables</a>
852</div>
853<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]854 <p>
855 This transformation analyzes and transforms the induction variables (and
856 computations derived from them) into simpler forms suitable for subsequent
857 analysis and transformation.
858 </p>
859
860 <p>
861 This transformation makes the following changes to each loop with an
862 identifiable induction variable:
863 </p>
864
865 <ol>
866 <li>All loops are transformed to have a <em>single</em> canonical
867 induction variable which starts at zero and steps by one.</li>
868 <li>The canonical induction variable is guaranteed to be the first PHI node
869 in the loop header block.</li>
870 <li>Any pointer arithmetic recurrences are raised to use array
871 subscripts.</li>
872 </ol>
873
874 <p>
875 If the trip count of a loop is computable, this pass also makes the following
876 changes:
877 </p>
878
879 <ol>
880 <li>The exit condition for the loop is canonicalized to compare the
881 induction value against the exit value. This turns loops like:
882 <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
883 into
884 <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
885 <li>Any use outside of the loop of an expression derived from the indvar
886 is changed to compute the derived value outside of the loop, eliminating
887 the dependence on the exit value of the induction variable. If the only
888 purpose of the loop is to compute the exit value of some derived
889 expression, this transformation will make the loop dead.</li>
Gordon Henriksene626bbe2007-11-04 16:17:00 +0000[diff] [blame]890 </ol>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]891
892 <p>
893 This transformation should be followed by strength reduction after all of the
894 desired loop transformations have been performed. Additionally, on targets
895 where it is profitable, the loop could be transformed to count down to zero
896 (the "do loop" optimization).
897 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]898</div>
899
900<!-------------------------------------------------------------------------- -->
901<div class="doc_subsection">
902 <a name="inline">Function Integration/Inlining</a>
903</div>
904<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]905 <p>
906 Bottom-up inlining of functions into callees.
907 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]908</div>
909
910<!-------------------------------------------------------------------------- -->
911<div class="doc_subsection">
912 <a name="insert-block-profiling">Insert instrumentation for block profiling</a>
913</div>
914<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]915 <p>
916 This pass instruments the specified program with counters for basic block
917 profiling, which counts the number of times each basic block executes. This
918 is the most basic form of profiling, which can tell which blocks are hot, but
919 cannot reliably detect hot paths through the CFG.
920 </p>
921
922 <p>
923 Note that this implementation is very naïve. Control equivalent regions of
924 the CFG should not require duplicate counters, but it does put duplicate
925 counters in.
926 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]927</div>
928
929<!-------------------------------------------------------------------------- -->
930<div class="doc_subsection">
931 <a name="insert-edge-profiling">Insert instrumentation for edge profiling</a>
932</div>
933<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]934 <p>
935 This pass instruments the specified program with counters for edge profiling.
936 Edge profiling can give a reasonable approximation of the hot paths through a
937 program, and is used for a wide variety of program transformations.
938 </p>
939
940 <p>
941 Note that this implementation is very naïve. It inserts a counter for
942 <em>every</em> edge in the program, instead of using control flow information
943 to prune the number of counters inserted.
944 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]945</div>
946
947<!-------------------------------------------------------------------------- -->
948<div class="doc_subsection">
949 <a name="insert-function-profiling">Insert instrumentation for function profiling</a>
950</div>
951<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]952 <p>
953 This pass instruments the specified program with counters for function
954 profiling, which counts the number of times each function is called.
955 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]956</div>
957
958<!-------------------------------------------------------------------------- -->
959<div class="doc_subsection">
960 <a name="insert-null-profiling-rs">Measure profiling framework overhead</a>
961</div>
962<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]963 <p>
964 The basic profiler that does nothing. It is the default profiler and thus
965 terminates <code>RSProfiler</code> chains. It is useful for measuring
966 framework overhead.
967 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]968</div>
969
970<!-------------------------------------------------------------------------- -->
971<div class="doc_subsection">
972 <a name="insert-rs-profiling-framework">Insert random sampling instrumentation framework</a>
973</div>
974<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]975 <p>
976 The second stage of the random-sampling instrumentation framework, duplicates
977 all instructions in a function, ignoring the profiling code, then connects the
978 two versions together at the entry and at backedges. At each connection point
979 a choice is made as to whether to jump to the profiled code (take a sample) or
980 execute the unprofiled code.
981 </p>
982
983 <p>
984 After this pass, it is highly recommended to run<a href="#mem2reg">mem2reg</a>
985 and <a href="#adce">adce</a>. <a href="#instcombine">instcombine</a>,
986 <a href="#load-vn">load-vn</a>, <a href="#gdce">gdce</a>, and
987 <a href="#dse">dse</a> also are good to run afterwards.
988 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]989</div>
990
991<!-------------------------------------------------------------------------- -->
992<div class="doc_subsection">
993 <a name="instcombine">Combine redundant instructions</a>
994</div>
995<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]996 <p>
997 Combine instructions to form fewer, simple
998 instructions. This pass does not modify the CFG This pass is where algebraic
999 simplification happens.
1000 </p>
1001
1002 <p>
1003 This pass combines things like:
1004 </p>
1005
1006<blockquote><pre
1007>%Y = add i32 %X, 1
1008%Z = add i32 %Y, 1</pre></blockquote>
1009
1010 <p>
1011 into:
1012 </p>
1013
1014<blockquote><pre
1015>%Z = add i32 %X, 2</pre></blockquote>
1016
1017 <p>
1018 This is a simple worklist driven algorithm.
1019 </p>
1020
1021 <p>
1022 This pass guarantees that the following canonicalizations are performed on
1023 the program:
1024 </p>
1025
1026 <ul>
1027 <li>If a binary operator has a constant operand, it is moved to the right-
1028 hand side.</li>
1029 <li>Bitwise operators with constant operands are always grouped so that
1030 shifts are performed first, then <code>or</code>s, then
1031 <code>and</code>s, then <code>xor</code>s.</li>
1032 <li>Compare instructions are converted from <code>&lt;</code>,
1033 <code>&gt;</code>, <code>≤</code>, or <code>≥</code> to
1034 <code>=</code> or <code>≠</code> if possible.</li>
1035 <li>All <code>cmp</code> instructions on boolean values are replaced with
1036 logical operations.</li>
1037 <li><code>add <var>X</var>, <var>X</var></code> is represented as
1038 <code>mul <var>X</var>, 2</code> ⇒ <code>shl <var>X</var>, 1</code></li>
1039 <li>Multiplies with a constant power-of-two argument are transformed into
1040 shifts.</li>
1041 <li>… etc.</li>
1042 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1043</div>
1044
1045<!-------------------------------------------------------------------------- -->
1046<div class="doc_subsection">
1047 <a name="internalize">Internalize Global Symbols</a>
1048</div>
1049<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1050 <p>
1051 This pass loops over all of the functions in the input module, looking for a
1052 main function. If a main function is found, all other functions and all
1053 global variables with initializers are marked as internal.
1054 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1055</div>
1056
1057<!-------------------------------------------------------------------------- -->
1058<div class="doc_subsection">
1059 <a name="ipconstprop">Interprocedural constant propagation</a>
1060</div>
1061<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1062 <p>
1063 This pass implements an <em>extremely</em> simple interprocedural constant
1064 propagation pass. It could certainly be improved in many different ways,
1065 like using a worklist. This pass makes arguments dead, but does not remove
1066 them. The existing dead argument elimination pass should be run after this
1067 to clean up the mess.
1068 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1069</div>
1070
1071<!-------------------------------------------------------------------------- -->
1072<div class="doc_subsection">
1073 <a name="ipsccp">Interprocedural Sparse Conditional Constant Propagation</a>
1074</div>
1075<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1076 <p>
1077 An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
1078 Propagation</a>.
1079 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1080</div>
1081
1082<!-------------------------------------------------------------------------- -->
1083<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1084 <a name="jump-threading">Thread control through conditional blocks</a>
1085</div>
1086<div class="doc_text">
1087 <p>
1088 Jump threading tries to find distinct threads of control flow running through
1089 a basic block. This pass looks at blocks that have multiple predecessors and
1090 multiple successors. If one or more of the predecessors of the block can be
1091 proven to always cause a jump to one of the successors, we forward the edge
1092 from the predecessor to the successor by duplicating the contents of this
1093 block.
1094 </p>
1095 <p>
1096 An example of when this can occur is code like this:
1097 </p>
1098
1099 <pre
1100>if () { ...
1101 X = 4;
1102}
1103if (X &lt; 3) {</pre>
1104
1105 <p>
1106 In this case, the unconditional branch at the end of the first if can be
1107 revectored to the false side of the second if.
1108 </p>
1109</div>
1110
1111<!-------------------------------------------------------------------------- -->
1112<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1113 <a name="lcssa">Loop-Closed SSA Form Pass</a>
1114</div>
1115<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1116 <p>
1117 This pass transforms loops by placing phi nodes at the end of the loops for
1118 all values that are live across the loop boundary. For example, it turns
1119 the left into the right code:
1120 </p>
1121
1122 <pre
1123>for (...) for (...)
1124 if (c) if (c)
1125 X1 = ... X1 = ...
1126 else else
1127 X2 = ... X2 = ...
1128 X3 = phi(X1, X2) X3 = phi(X1, X2)
1129... = X3 + 4 X4 = phi(X3)
1130 ... = X4 + 4</pre>
1131
1132 <p>
1133 This is still valid LLVM; the extra phi nodes are purely redundant, and will
1134 be trivially eliminated by <code>InstCombine</code>. The major benefit of
1135 this transformation is that it makes many other loop optimizations, such as
1136 LoopUnswitching, simpler.
1137 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1138</div>
1139
1140<!-------------------------------------------------------------------------- -->
1141<div class="doc_subsection">
1142 <a name="licm">Loop Invariant Code Motion</a>
1143</div>
1144<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1145 <p>
1146 This pass performs loop invariant code motion, attempting to remove as much
1147 code from the body of a loop as possible. It does this by either hoisting
1148 code into the preheader block, or by sinking code to the exit blocks if it is
1149 safe. This pass also promotes must-aliased memory locations in the loop to
1150 live in registers, thus hoisting and sinking "invariant" loads and stores.
1151 </p>
1152
1153 <p>
1154 This pass uses alias analysis for two purposes:
1155 </p>
1156
1157 <ul>
1158 <li>Moving loop invariant loads and calls out of loops. If we can determine
1159 that a load or call inside of a loop never aliases anything stored to,
1160 we can hoist it or sink it like any other instruction.</li>
1161 <li>Scalar Promotion of Memory - If there is a store instruction inside of
1162 the loop, we try to move the store to happen AFTER the loop instead of
1163 inside of the loop. This can only happen if a few conditions are true:
1164 <ul>
1165 <li>The pointer stored through is loop invariant.</li>
1166 <li>There are no stores or loads in the loop which <em>may</em> alias
1167 the pointer. There are no calls in the loop which mod/ref the
1168 pointer.</li>
1169 </ul>
1170 If these conditions are true, we can promote the loads and stores in the
1171 loop of the pointer to use a temporary alloca'd variable. We then use
1172 the mem2reg functionality to construct the appropriate SSA form for the
1173 variable.</li>
1174 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1175</div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1176<!-------------------------------------------------------------------------- -->
1177<div class="doc_subsection">
1178 <a name="loop-deletion">Dead Loop Deletion Pass</a>
1179</div>
1180<div class="doc_text">
1181 <p>
1182 This file implements the Dead Loop Deletion Pass. This pass is responsible
1183 for eliminating loops with non-infinite computable trip counts that have no
1184 side effects or volatile instructions, and do not contribute to the
1185 computation of the function's return value.
1186 </p>
1187</div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1188
1189<!-------------------------------------------------------------------------- -->
1190<div class="doc_subsection">
1191 <a name="loop-extract">Extract loops into new functions</a>
1192</div>
1193<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1194 <p>
1195 A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
1196 extract each top-level loop into its own new function. If the loop is the
1197 <em>only</em> loop in a given function, it is not touched. This is a pass most
1198 useful for debugging via bugpoint.
1199 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1200</div>
1201
1202<!-------------------------------------------------------------------------- -->
1203<div class="doc_subsection">
1204 <a name="loop-extract-single">Extract at most one loop into a new function</a>
1205</div>
1206<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1207 <p>
1208 Similar to <a href="#loop-extract">Extract loops into new functions</a>,
1209 this pass extracts one natural loop from the program into a function if it
1210 can. This is used by bugpoint.
1211 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1212</div>
1213
1214<!-------------------------------------------------------------------------- -->
1215<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1216 <a name="loop-index-split">Index Split Loops</a>
1217</div>
1218<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1219 <p>
1220 This pass divides loop's iteration range by spliting loop such that each
1221 individual loop is executed efficiently.
1222 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1223</div>
1224
1225<!-------------------------------------------------------------------------- -->
1226<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1227 <a name="loop-reduce">Loop Strength Reduction</a>
1228</div>
1229<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1230 <p>
1231 This pass performs a strength reduction on array references inside loops that
1232 have as one or more of their components the loop induction variable. This is
1233 accomplished by creating a new value to hold the initial value of the array
1234 access for the first iteration, and then creating a new GEP instruction in
1235 the loop to increment the value by the appropriate amount.
1236 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1237</div>
1238
1239<!-------------------------------------------------------------------------- -->
1240<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1241 <a name="loop-rotate">Rotate Loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1242</div>
1243<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1244 <p>A simple loop rotation transformation.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1245</div>
1246
1247<!-------------------------------------------------------------------------- -->
1248<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1249 <a name="loop-unroll">Unroll loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1250</div>
1251<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1252 <p>
1253 This pass implements a simple loop unroller. It works best when loops have
1254 been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
1255 allowing it to determine the trip counts of loops easily.
1256 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1257</div>
1258
1259<!-------------------------------------------------------------------------- -->
1260<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1261 <a name="loop-unswitch">Unswitch loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1262</div>
1263<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1264 <p>
1265 This pass transforms loops that contain branches on loop-invariant conditions
1266 to have multiple loops. For example, it turns the left into the right code:
1267 </p>
1268
1269 <pre
1270>for (...) if (lic)
1271 A for (...)
1272 if (lic) A; B; C
1273 B else
1274 C for (...)
1275 A; C</pre>
1276
1277 <p>
1278 This can increase the size of the code exponentially (doubling it every time
1279 a loop is unswitched) so we only unswitch if the resultant code will be
1280 smaller than a threshold.
1281 </p>
1282
1283 <p>
1284 This pass expects LICM to be run before it to hoist invariant conditions out
1285 of the loop, to make the unswitching opportunity obvious.
1286 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1287</div>
1288
1289<!-------------------------------------------------------------------------- -->
1290<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1291 <a name="loopsimplify">Canonicalize natural loops</a>
1292</div>
1293<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1294 <p>
1295 This pass performs several transformations to transform natural loops into a
1296 simpler form, which makes subsequent analyses and transformations simpler and
1297 more effective.
1298 </p>
1299
1300 <p>
1301 Loop pre-header insertion guarantees that there is a single, non-critical
1302 entry edge from outside of the loop to the loop header. This simplifies a
1303 number of analyses and transformations, such as LICM.
1304 </p>
1305
1306 <p>
1307 Loop exit-block insertion guarantees that all exit blocks from the loop
1308 (blocks which are outside of the loop that have predecessors inside of the
1309 loop) only have predecessors from inside of the loop (and are thus dominated
1310 by the loop header). This simplifies transformations such as store-sinking
1311 that are built into LICM.
1312 </p>
1313
1314 <p>
1315 This pass also guarantees that loops will have exactly one backedge.
1316 </p>
1317
1318 <p>
1319 Note that the simplifycfg pass will clean up blocks which are split out but
1320 end up being unnecessary, so usage of this pass should not pessimize
1321 generated code.
1322 </p>
1323
1324 <p>
1325 This pass obviously modifies the CFG, but updates loop information and
1326 dominator information.
1327 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1328</div>
1329
1330<!-------------------------------------------------------------------------- -->
1331<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1332 <a name="lowerallocs">Lower allocations from instructions to calls</a>
1333</div>
1334<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1335 <p>
1336 Turn <tt>malloc</tt> and <tt>free</tt> instructions into <tt>@malloc</tt> and
1337 <tt>@free</tt> calls.
1338 </p>
1339
1340 <p>
1341 This is a target-dependent tranformation because it depends on the size of
1342 data types and alignment constraints.
1343 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1344</div>
1345
1346<!-------------------------------------------------------------------------- -->
1347<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1348 <a name="lowerinvoke">Lower invoke and unwind, for unwindless code generators</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1349</div>
1350<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1351 <p>
1352 This transformation is designed for use by code generators which do not yet
1353 support stack unwinding. This pass supports two models of exception handling
1354 lowering, the 'cheap' support and the 'expensive' support.
1355 </p>
1356
1357 <p>
1358 'Cheap' exception handling support gives the program the ability to execute
1359 any program which does not "throw an exception", by turning 'invoke'
1360 instructions into calls and by turning 'unwind' instructions into calls to
1361 abort(). If the program does dynamically use the unwind instruction, the
1362 program will print a message then abort.
1363 </p>
1364
1365 <p>
1366 'Expensive' exception handling support gives the full exception handling
1367 support to the program at the cost of making the 'invoke' instruction
1368 really expensive. It basically inserts setjmp/longjmp calls to emulate the
1369 exception handling as necessary.
1370 </p>
1371
1372 <p>
1373 Because the 'expensive' support slows down programs a lot, and EH is only
1374 used for a subset of the programs, it must be specifically enabled by the
1375 <tt>-enable-correct-eh-support</tt> option.
1376 </p>
1377
1378 <p>
1379 Note that after this pass runs the CFG is not entirely accurate (exceptional
1380 control flow edges are not correct anymore) so only very simple things should
1381 be done after the lowerinvoke pass has run (like generation of native code).
1382 This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
1383 support the invoke instruction yet" lowering pass.
1384 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1385</div>
1386
1387<!-------------------------------------------------------------------------- -->
1388<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1389 <a name="lowersetjmp">Lower Set Jump</a>
1390</div>
1391<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1392 <p>
1393 Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
1394 instructions as necessary.
1395 </p>
1396
1397 <p>
1398 Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
1399 call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
1400 This unwinds the stack for us calling all of the destructors for
1401 objects allocated on the stack.
1402 </p>
1403
1404 <p>
1405 At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
1406 removed. The calls in a function that have a <tt>setjmp</tt> are converted to
1407 invoke where the except part checks to see if it's a <tt>longjmp</tt>
1408 exception and, if so, if it's handled in the function. If it is, then it gets
1409 the value returned by the <tt>longjmp</tt> and goes to where the basic block
1410 was split. <tt>invoke</tt> instructions are handled in a similar fashion with
1411 the original except block being executed if it isn't a <tt>longjmp</tt>
1412 except that is handled by that function.
1413 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1414</div>
1415
1416<!-------------------------------------------------------------------------- -->
1417<div class="doc_subsection">
1418 <a name="lowerswitch">Lower SwitchInst's to branches</a>
1419</div>
1420<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1421 <p>
1422 Rewrites <tt>switch</tt> instructions with a sequence of branches, which
1423 allows targets to get away with not implementing the switch instruction until
1424 it is convenient.
1425 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1426</div>
1427
1428<!-------------------------------------------------------------------------- -->
1429<div class="doc_subsection">
1430 <a name="mem2reg">Promote Memory to Register</a>
1431</div>
1432<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1433 <p>
1434 This file promotes memory references to be register references. It promotes
1435 <tt>alloca</tt> instructions which only have <tt>load</tt>s and
1436 <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
1437 frontiers to place <tt>phi</tt> nodes, then traversing the function in
1438 depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
1439 appropriate. This is just the standard SSA construction algorithm to construct
1440 "pruned" SSA form.
1441 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1442</div>
1443
1444<!-------------------------------------------------------------------------- -->
1445<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1446 <a name="memcpyopt">Optimize use of memcpy and friend</a>
1447</div>
1448<div class="doc_text">
1449 <p>
1450 This pass performs various transformations related to eliminating memcpy
1451 calls, or transforming sets of stores into memset's.
1452 </p>
1453</div>
1454
1455<!-------------------------------------------------------------------------- -->
1456<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1457 <a name="mergereturn">Unify function exit nodes</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1458</div>
1459<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1460 <p>
1461 Ensure that functions have at most one <tt>ret</tt> instruction in them.
1462 Additionally, it keeps track of which node is the new exit node of the CFG.
1463 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1464</div>
1465
1466<!-------------------------------------------------------------------------- -->
1467<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1468 <a name="prune-eh">Remove unused exception handling info</a>
1469</div>
1470<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1471 <p>
1472 This file implements a simple interprocedural pass which walks the call-graph,
1473 turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
1474 only if the callee cannot throw an exception. It implements this as a
1475 bottom-up traversal of the call-graph.
1476 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1477</div>
1478
1479<!-------------------------------------------------------------------------- -->
1480<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1481 <a name="reassociate">Reassociate expressions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1482</div>
1483<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1484 <p>
1485 This pass reassociates commutative expressions in an order that is designed
1486 to promote better constant propagation, GCSE, LICM, PRE, etc.
1487 </p>
1488
1489 <p>
1490 For example: 4 + (<var>x</var> + 5) ⇒ <var>x</var> + (4 + 5)
1491 </p>
1492
1493 <p>
1494 In the implementation of this algorithm, constants are assigned rank = 0,
1495 function arguments are rank = 1, and other values are assigned ranks
1496 corresponding to the reverse post order traversal of current function
1497 (starting at 2), which effectively gives values in deep loops higher rank
1498 than values not in loops.
1499 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1500</div>
1501
1502<!-------------------------------------------------------------------------- -->
1503<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1504 <a name="reg2mem">Demote all values to stack slots</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1505</div>
1506<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1507 <p>
1508 This file demotes all registers to memory references. It is intented to be
1509 the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]1510 <tt>load</tt> instructions, the only values live across basic blocks are
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1511 <tt>alloca</tt> instructions and <tt>load</tt> instructions before
1512 <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
1513 easier. To make later hacking easier, the entry block is split into two, such
1514 that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
1515 entry block.
1516 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1517</div>
1518
1519<!-------------------------------------------------------------------------- -->
1520<div class="doc_subsection">
1521 <a name="scalarrepl">Scalar Replacement of Aggregates</a>
1522</div>
1523<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1524 <p>
1525 The well-known scalar replacement of aggregates transformation. This
1526 transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
1527 or array) into individual <tt>alloca</tt> instructions for each member if
1528 possible. Then, if possible, it transforms the individual <tt>alloca</tt>
1529 instructions into nice clean scalar SSA form.
1530 </p>
1531
1532 <p>
1533 This combines a simple scalar replacement of aggregates algorithm with the <a
1534 href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
1535 especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
1536 then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
1537 promote works well.
1538 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1539</div>
1540
1541<!-------------------------------------------------------------------------- -->
1542<div class="doc_subsection">
1543 <a name="sccp">Sparse Conditional Constant Propagation</a>
1544</div>
1545<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1546 <p>
1547 Sparse conditional constant propagation and merging, which can be summarized
1548 as:
1549 </p>
1550
1551 <ol>
1552 <li>Assumes values are constant unless proven otherwise</li>
1553 <li>Assumes BasicBlocks are dead unless proven otherwise</li>
1554 <li>Proves values to be constant, and replaces them with constants</li>
1555 <li>Proves conditional branches to be unconditional</li>
1556 </ol>
1557
1558 <p>
1559 Note that this pass has a habit of making definitions be dead. It is a good
1560 idea to to run a DCE pass sometime after running this pass.
1561 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1562</div>
1563
1564<!-------------------------------------------------------------------------- -->
1565<div class="doc_subsection">
1566 <a name="simplify-libcalls">Simplify well-known library calls</a>
1567</div>
1568<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1569 <p>
1570 Applies a variety of small optimizations for calls to specific well-known
1571 function calls (e.g. runtime library functions). For example, a call
1572 <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
1573 transformed into simply <tt>return 3</tt>.
1574 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1575</div>
1576
1577<!-------------------------------------------------------------------------- -->
1578<div class="doc_subsection">
1579 <a name="simplifycfg">Simplify the CFG</a>
1580</div>
1581<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1582 <p>
1583 Performs dead code elimination and basic block merging. Specifically:
1584 </p>
1585
1586 <ol>
1587 <li>Removes basic blocks with no predecessors.</li>
1588 <li>Merges a basic block into its predecessor if there is only one and the
1589 predecessor only has one successor.</li>
1590 <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
1591 <li>Eliminates a basic block that only contains an unconditional
1592 branch.</li>
1593 </ol>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1594</div>
1595
1596<!-------------------------------------------------------------------------- -->
1597<div class="doc_subsection">
1598 <a name="strip">Strip all symbols from a module</a>
1599</div>
1600<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1601 <p>
1602 Performs code stripping. This transformation can delete:
1603 </p>
1604
1605 <ol>
1606 <li>names for virtual registers</li>
1607 <li>symbols for internal globals and functions</li>
1608 <li>debug information</li>
1609 </ol>
1610
1611 <p>
1612 Note that this transformation makes code much less readable, so it should
1613 only be used in situations where the <tt>strip</tt> utility would be used,
1614 such as reducing code size or making it harder to reverse engineer code.
1615 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1616</div>
1617
1618<!-------------------------------------------------------------------------- -->
1619<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1620 <a name="strip-dead-prototypes">Remove unused function declarations</a>
1621</div>
1622<div class="doc_text">
1623 <p>
1624 This pass loops over all of the functions in the input module, looking for
1625 dead declarations and removes them. Dead declarations are declarations of
1626 functions for which no implementation is available (i.e., declarations for
1627 unused library functions).
1628 </p>
1629</div>
1630
1631<!-------------------------------------------------------------------------- -->
1632<div class="doc_subsection">
1633 <a name="sretpromotion">Promote sret arguments</a>
1634</div>
1635<div class="doc_text">
1636 <p>
1637 This pass finds functions that return a struct (using a pointer to the struct
1638 as the first argument of the function, marked with the '<tt>sret</tt>' attribute) and
1639 replaces them with a new function that simply returns each of the elements of
1640 that struct (using multiple return values).
1641 </p>
1642
1643 <p>
1644 This pass works under a number of conditions:
1645 </p>
1646
1647 <ul>
1648 <li>The returned struct must not contain other structs</li>
1649 <li>The returned struct must only be used to load values from</li>
1650 <li>The placeholder struct passed in is the result of an <tt>alloca</tt></li>
1651 </ul>
1652</div>
1653
1654<!-------------------------------------------------------------------------- -->
1655<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1656 <a name="tailcallelim">Tail Call Elimination</a>
1657</div>
1658<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1659 <p>
1660 This file transforms calls of the current function (self recursion) followed
1661 by a return instruction with a branch to the entry of the function, creating
1662 a loop. This pass also implements the following extensions to the basic
1663 algorithm:
1664 </p>
1665
1666 <ul>
1667 <li>Trivial instructions between the call and return do not prevent the
1668 transformation from taking place, though currently the analysis cannot
1669 support moving any really useful instructions (only dead ones).
1670 <li>This pass transforms functions that are prevented from being tail
1671 recursive by an associative expression to use an accumulator variable,
1672 thus compiling the typical naive factorial or <tt>fib</tt> implementation
1673 into efficient code.
1674 <li>TRE is performed if the function returns void, if the return
1675 returns the result returned by the call, or if the function returns a
1676 run-time constant on all exits from the function. It is possible, though
1677 unlikely, that the return returns something else (like constant 0), and
1678 can still be TRE'd. It can be TRE'd if <em>all other</em> return
1679 instructions in the function return the exact same value.
1680 <li>If it can prove that callees do not access theier caller stack frame,
1681 they are marked as eligible for tail call elimination (by the code
1682 generator).
1683 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1684</div>
1685
1686<!-------------------------------------------------------------------------- -->
1687<div class="doc_subsection">
1688 <a name="tailduplicate">Tail Duplication</a>
1689</div>
1690<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1691 <p>
1692 This pass performs a limited form of tail duplication, intended to simplify
1693 CFGs by removing some unconditional branches. This pass is necessary to
1694 straighten out loops created by the C front-end, but also is capable of
1695 making other code nicer. After this pass is run, the CFG simplify pass
1696 should be run to clean up the mess.
1697 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1698</div>
1699
1700<!-- ======================================================================= -->
1701<div class="doc_section"> <a name="transform">Utility Passes</a></div>
1702<div class="doc_text">
1703 <p>This section describes the LLVM Utility Passes.</p>
1704</div>
1705
1706<!-------------------------------------------------------------------------- -->
1707<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1708 <a name="deadarghaX0r">Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1709</div>
1710<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1711 <p>
1712 Same as dead argument elimination, but deletes arguments to functions which
1713 are external. This is only for use by <a
1714 href="Bugpoint.html">bugpoint</a>.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1715</div>
1716
1717<!-------------------------------------------------------------------------- -->
1718<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1719 <a name="extract-blocks">Extract Basic Blocks From Module (for bugpoint use)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1720</div>
1721<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1722 <p>
1723 This pass is used by bugpoint to extract all blocks from the module into their
1724 own functions.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1725</div>
1726
1727<!-------------------------------------------------------------------------- -->
1728<div class="doc_subsection">
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]1729 <a name="preverify">Preliminary module verification</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1730</div>
1731<div class="doc_text">
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]1732 <p>
1733 Ensures that the module is in the form required by the <a
1734 href="#verifier">Module Verifier</a> pass.
1735 </p>
1736
1737 <p>
1738 Running the verifier runs this pass automatically, so there should be no need
1739 to use it directly.
1740 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1741</div>
1742
1743<!-------------------------------------------------------------------------- -->
1744<div class="doc_subsection">
1745 <a name="verify">Module Verifier</a>
1746</div>
1747<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1748 <p>
1749 Verifies an LLVM IR code. This is useful to run after an optimization which is
1750 undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
1751 emitting bitcode, and also that malformed bitcode is likely to make LLVM
1752 crash. All language front-ends are therefore encouraged to verify their output
1753 before performing optimizing transformations.
1754 </p>
1755
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1756 <ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1757 <li>Both of a binary operator's parameters are of the same type.</li>
1758 <li>Verify that the indices of mem access instructions match other
1759 operands.</li>
1760 <li>Verify that arithmetic and other things are only performed on
1761 first-class types. Verify that shifts and logicals only happen on
1762 integrals f.e.</li>
1763 <li>All of the constants in a switch statement are of the correct type.</li>
1764 <li>The code is in valid SSA form.</li>
Chris Lattner46b3abc2009-10-28 04:47:06 +0000[diff] [blame]1765 <li>It is illegal to put a label into any other type (like a structure) or
1766 to return one.</li>
Nick Lewycky0c78ac12008-03-28 06:46:51 +0000[diff] [blame]1767 <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]1768 invalid.</li>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1769 <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
1770 <li>PHI nodes must be the first thing in a basic block, all grouped
1771 together.</li>
1772 <li>PHI nodes must have at least one entry.</li>
1773 <li>All basic blocks should only end with terminator insts, not contain
1774 them.</li>
1775 <li>The entry node to a function must not have predecessors.</li>
1776 <li>All Instructions must be embedded into a basic block.</li>
1777 <li>Functions cannot take a void-typed parameter.</li>
1778 <li>Verify that a function's argument list agrees with its declared
1779 type.</li>
1780 <li>It is illegal to specify a name for a void value.</li>
1781 <li>It is illegal to have a internal global value with no initializer.</li>
1782 <li>It is illegal to have a ret instruction that returns a value that does
1783 not agree with the function return value type.</li>
1784 <li>Function call argument types match the function prototype.</li>
1785 <li>All other things that are tested by asserts spread about the code.</li>
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1786 </ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1787
1788 <p>
1789 Note that this does not provide full security verification (like Java), but
1790 instead just tries to ensure that code is well-formed.
1791 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1792</div>
1793
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1794<!-------------------------------------------------------------------------- -->
1795<div class="doc_subsection">
1796 <a name="view-cfg">View CFG of function</a>
1797</div>
1798<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1799 <p>
1800 Displays the control flow graph using the GraphViz tool.
1801 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1802</div>
1803
1804<!-------------------------------------------------------------------------- -->
1805<div class="doc_subsection">
1806 <a name="view-cfg-only">View CFG of function (with no function bodies)</a>
1807</div>
1808<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1809 <p>
1810 Displays the control flow graph using the GraphViz tool, but omitting function
1811 bodies.
1812 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1813</div>
1814
Tobias Grosser733783b2010-05-07 09:33:18 +0000[diff] [blame]1815<!-------------------------------------------------------------------------- -->
1816<div class="doc_subsection">
1817 <a name="view-dom">View dominator tree of function</a>
1818</div>
1819<div class="doc_text">
1820 <p>
1821 Displays the dominator tree using the GraphViz tool.
1822 </p>
1823</div>
1824
1825<!-------------------------------------------------------------------------- -->
1826<div class="doc_subsection">
1827 <a name="view-dom-only">View dominator tree of function (with no function
1828 bodies)
1829 </a>
1830</div>
1831<div class="doc_text">
1832 <p>
1833 Displays the dominator tree using the GraphViz tool, but omitting function
1834 bodies.
1835 </p>
1836</div>
1837
1838<!-------------------------------------------------------------------------- -->
1839<div class="doc_subsection">
1840 <a name="view-postdom">View post dominator tree of function</a>
1841</div>
1842<div class="doc_text">
1843 <p>
1844 Displays the post dominator tree using the GraphViz tool.
1845 </p>
1846</div>
1847
1848<!-------------------------------------------------------------------------- -->
1849<div class="doc_subsection">
1850 <a name="view-postdom-only">View post dominator tree of function (with no
1851 function bodies)
1852 </a>
1853</div>
1854<div class="doc_text">
1855 <p>
1856 Displays the post dominator tree using the GraphViz tool, but omitting
1857 function bodies.
1858 </p>
1859</div>
1860
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1861<!-- *********************************************************************** -->
1862
1863<hr>
1864<address>
1865 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1869
1870 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
1871 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
1872 Last modified: $Date$
1873</address>
1874
1875</body>
1876</html>