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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>
78<tr><td><a href="#anders-aa">-anders-aa</a></td><td>Andersen's Interprocedural Alias Analysis</td></tr>
79<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (default AA impl)</td></tr>
80<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]81<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]82<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
83<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
84<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]85<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]86<tr><td><a href="#dot-callgraph">-dot-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
87<tr><td><a href="#dot-cfg">-dot-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
88<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>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]89<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]90<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
91<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]92<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Construction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]93<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]94<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
95<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
96<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]97<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]98<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]99<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
100<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
101<tr><td><a href="#print-cfg-sccs">-print-cfg-sccs</a></td><td>Print SCCs of each function CFG</td></tr>
102<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
103<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
104<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
105<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]106<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
107<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
108<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
109
110
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]111<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
112<tr><th>Option</th><th>Name</th></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]113<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
114<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
115<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]116<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]117<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]118<tr><td><a href="#condprop">-condprop</a></td><td>Conditional Propagation</td></tr>
119<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
120<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
121<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
122<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
123<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
124<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
125<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]126<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
127<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]128<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]129<tr><td><a href="#indmemrem">-indmemrem</a></td><td>Indirect Malloc and Free Removal</td></tr>
130<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
131<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
132<tr><td><a href="#insert-block-profiling">-insert-block-profiling</a></td><td>Insert instrumentation for block profiling</td></tr>
133<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
134<tr><td><a href="#insert-function-profiling">-insert-function-profiling</a></td><td>Insert instrumentation for function profiling</td></tr>
135<tr><td><a href="#insert-null-profiling-rs">-insert-null-profiling-rs</a></td><td>Measure profiling framework overhead</td></tr>
136<tr><td><a href="#insert-rs-profiling-framework">-insert-rs-profiling-framework</a></td><td>Insert random sampling instrumentation framework</td></tr>
137<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
138<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
139<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
140<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]141<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]142<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
143<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]144<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]145<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
146<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]147<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]148<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]149<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
150<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
151<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
152<tr><td><a href="#loopsimplify">-loopsimplify</a></td><td>Canonicalize natural loops</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]153<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]154<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]155<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
156<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
157<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]158<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]159<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]160<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]161<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
162<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]163<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates</td></tr>
164<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
165<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
166<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
167<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]168<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Remove unused function declarations</td></tr>
169<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]170<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
171<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]172
173
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]174<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
175<tr><th>Option</th><th>Name</th></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]176<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
177<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]178<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]179<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]180<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
181<tr><td><a href="#view-cfg-only">-view-cfg-only</a></td><td>View CFG of function (with no function bodies)</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]182</table>
183</div>
184
185<!-- ======================================================================= -->
186<div class="doc_section"> <a name="example">Analysis Passes</a></div>
187<div class="doc_text">
188 <p>This section describes the LLVM Analysis Passes.</p>
189</div>
190
191<!-------------------------------------------------------------------------- -->
192<div class="doc_subsection">
193 <a name="aa-eval">Exhaustive Alias Analysis Precision Evaluator</a>
194</div>
195<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]196 <p>This is a simple N^2 alias analysis accuracy evaluator.
197 Basically, for each function in the program, it simply queries to see how the
198 alias analysis implementation answers alias queries between each pair of
199 pointers in the function.</p>
200
201 <p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
202 Spadini, and Wojciech Stryjewski.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]203</div>
204
205<!-------------------------------------------------------------------------- -->
206<div class="doc_subsection">
207 <a name="anders-aa">Andersen's Interprocedural Alias Analysis</a>
208</div>
209<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]210 <p>
211 This is an implementation of Andersen's interprocedural alias
212 analysis
213 </p>
214
215 <p>
216 In pointer analysis terms, this is a subset-based, flow-insensitive,
217 field-sensitive, and context-insensitive algorithm pointer algorithm.
218 </p>
219
220 <p>
221 This algorithm is implemented as three stages:
222 </p>
223
224 <ol>
225 <li>Object identification.</li>
226 <li>Inclusion constraint identification.</li>
227 <li>Offline constraint graph optimization.</li>
228 <li>Inclusion constraint solving.</li>
229 </ol>
230
231 <p>
232 The object identification stage identifies all of the memory objects in the
233 program, which includes globals, heap allocated objects, and stack allocated
234 objects.
235 </p>
236
237 <p>
238 The inclusion constraint identification stage finds all inclusion constraints
239 in the program by scanning the program, looking for pointer assignments and
240 other statements that effect the points-to graph. For a statement like
241 <code><var>A</var> = <var>B</var></code>, this statement is processed to
242 indicate that <var>A</var> can point to anything that <var>B</var> can point
243 to. Constraints can handle copies, loads, and stores, and address taking.
244 </p>
245
246 <p>
247 The offline constraint graph optimization portion includes offline variable
248 substitution algorithms intended to computer pointer and location
249 equivalences. Pointer equivalences are those pointers that will have the
250 same points-to sets, and location equivalences are those variables that
251 always appear together in points-to sets.
252 </p>
253
254 <p>
255 The inclusion constraint solving phase iteratively propagates the inclusion
256 constraints until a fixed point is reached. This is an O(<var>n</var>³)
257 algorithm.
258 </p>
259
260 <p>
261 Function constraints are handled as if they were structs with <var>X</var>
262 fields. Thus, an access to argument <var>X</var> of function <var>Y</var> is
263 an access to node index <code>getNode(<var>Y</var>) + <var>X</var></code>.
264 This representation allows handling of indirect calls without any issues. To
265 wit, an indirect call <code><var>Y</var>(<var>a</var>,<var>b</var>)</code> is
266 equivalent to <code>*(<var>Y</var> + 1) = <var>a</var>, *(<var>Y</var> + 2) =
267 <var>b</var></code>. The return node for a function <var>F</var> is always
268 located at <code>getNode(<var>F</var>) + CallReturnPos</code>. The arguments
269 start at <code>getNode(<var>F</var>) + CallArgPos</code>.
270 </p>
Chris Lattnerb80e1ab2009-08-28 00:45:47 +0000[diff] [blame]271
272 <p>
273 Please keep in mind that the current andersen's pass has many known
274 problems and bugs. It should be considered "research quality".
275 </p>
276
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]277</div>
278
279<!-------------------------------------------------------------------------- -->
280<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]281 <a name="basicaa">Basic Alias Analysis (default AA impl)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]282</div>
283<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]284 <p>
285 This is the default implementation of the Alias Analysis interface
286 that simply implements a few identities (two different globals cannot alias,
287 etc), but otherwise does no analysis.
288 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]289</div>
290
291<!-------------------------------------------------------------------------- -->
292<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]293 <a name="basiccg">Basic CallGraph Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]294</div>
295<div class="doc_text">
296 <p>Yet to be written.</p>
297</div>
298
299<!-------------------------------------------------------------------------- -->
300<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]301 <a name="codegenprepare">Optimize for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]302</div>
303<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]304 <p>
305 This pass munges the code in the input function to better prepare it for
306 SelectionDAG-based code generation. This works around limitations in it's
307 basic-block-at-a-time approach. It should eventually be removed.
308 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]309</div>
310
311<!-------------------------------------------------------------------------- -->
312<div class="doc_subsection">
313 <a name="count-aa">Count Alias Analysis Query Responses</a>
314</div>
315<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]316 <p>
317 A pass which can be used to count how many alias queries
318 are being made and how the alias analysis implementation being used responds.
319 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]320</div>
321
322<!-------------------------------------------------------------------------- -->
323<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]324 <a name="debug-aa">AA use debugger</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]325</div>
326<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]327 <p>
328 This simple pass checks alias analysis users to ensure that if they
329 create a new value, they do not query AA without informing it of the value.
330 It acts as a shim over any other AA pass you want.
331 </p>
332
333 <p>
334 Yes keeping track of every value in the program is expensive, but this is
335 a debugging pass.
336 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]337</div>
338
339<!-------------------------------------------------------------------------- -->
340<div class="doc_subsection">
341 <a name="domfrontier">Dominance Frontier Construction</a>
342</div>
343<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]344 <p>
345 This pass is a simple dominator construction algorithm for finding forward
346 dominator frontiers.
347 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]348</div>
349
350<!-------------------------------------------------------------------------- -->
351<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]352 <a name="domtree">Dominator Tree Construction</a>
353</div>
354<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]355 <p>
356 This pass is a simple dominator construction algorithm for finding forward
357 dominators.
358 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]359</div>
360
361<!-------------------------------------------------------------------------- -->
362<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]363 <a name="dot-callgraph">Print Call Graph to 'dot' file</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]364</div>
365<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]366 <p>
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]367 This pass, only available in <code>opt</code>, prints the call graph into a
368 <code>.dot</code> graph. This graph can then be processed with the "dot" tool
369 to convert it to postscript or some other suitable format.
370 </p>
371</div>
372
373<!-------------------------------------------------------------------------- -->
374<div class="doc_subsection">
375 <a name="dot-cfg">Print CFG of function to 'dot' file</a>
376</div>
377<div class="doc_text">
378 <p>
379 This pass, only available in <code>opt</code>, prints the control flow graph
380 into a <code>.dot</code> graph. This graph can then be processed with the
381 "dot" tool to convert it to postscript or some other suitable format.
382 </p>
383</div>
384
385<!-------------------------------------------------------------------------- -->
386<div class="doc_subsection">
387 <a name="dot-cfg-only">Print CFG of function to 'dot' file (with no function bodies)</a>
388</div>
389<div class="doc_text">
390 <p>
391 This pass, only available in <code>opt</code>, prints the control flow graph
392 into a <code>.dot</code> graph, omitting the function bodies. This graph can
393 then be processed with the "dot" tool to convert it to postscript or some
394 other suitable format.
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]395 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]396</div>
397
398<!-------------------------------------------------------------------------- -->
399<div class="doc_subsection">
400 <a name="globalsmodref-aa">Simple mod/ref analysis for globals</a>
401</div>
402<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]403 <p>
404 This simple pass provides alias and mod/ref information for global values
405 that do not have their address taken, and keeps track of whether functions
406 read or write memory (are "pure"). For this simple (but very common) case,
407 we can provide pretty accurate and useful information.
408 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]409</div>
410
411<!-------------------------------------------------------------------------- -->
412<div class="doc_subsection">
413 <a name="instcount">Counts the various types of Instructions</a>
414</div>
415<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]416 <p>
417 This pass collects the count of all instructions and reports them
418 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]419</div>
420
421<!-------------------------------------------------------------------------- -->
422<div class="doc_subsection">
423 <a name="intervals">Interval Partition Construction</a>
424</div>
425<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]426 <p>
427 This analysis calculates and represents the interval partition of a function,
428 or a preexisting interval partition.
429 </p>
430
431 <p>
432 In this way, the interval partition may be used to reduce a flow graph down
433 to its degenerate single node interval partition (unless it is irreducible).
434 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]435</div>
436
437<!-------------------------------------------------------------------------- -->
438<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]439 <a name="loops">Natural Loop Construction</a>
440</div>
441<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]442 <p>
443 This analysis is used to identify natural loops and determine the loop depth
444 of various nodes of the CFG. Note that the loops identified may actually be
445 several natural loops that share the same header node... not just a single
446 natural loop.
447 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]448</div>
449
450<!-------------------------------------------------------------------------- -->
451<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]452 <a name="memdep">Memory Dependence Analysis</a>
453</div>
454<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]455 <p>
456 An analysis that determines, for a given memory operation, what preceding
457 memory operations it depends on. It builds on alias analysis information, and
458 tries to provide a lazy, caching interface to a common kind of alias
459 information query.
460 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]461</div>
462
463<!-------------------------------------------------------------------------- -->
464<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]465 <a name="no-aa">No Alias Analysis (always returns 'may' alias)</a>
466</div>
467<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]468 <p>
469 Always returns "I don't know" for alias queries. NoAA is unlike other alias
470 analysis implementations, in that it does not chain to a previous analysis. As
471 such it doesn't follow many of the rules that other alias analyses must.
472 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]473</div>
474
475<!-------------------------------------------------------------------------- -->
476<div class="doc_subsection">
477 <a name="no-profile">No Profile Information</a>
478</div>
479<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]480 <p>
481 The default "no profile" implementation of the abstract
482 <code>ProfileInfo</code> interface.
483 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]484</div>
485
486<!-------------------------------------------------------------------------- -->
487<div class="doc_subsection">
488 <a name="postdomfrontier">Post-Dominance Frontier Construction</a>
489</div>
490<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]491 <p>
492 This pass is a simple post-dominator construction algorithm for finding
493 post-dominator frontiers.
494 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]495</div>
496
497<!-------------------------------------------------------------------------- -->
498<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]499 <a name="postdomtree">Post-Dominator Tree Construction</a>
500</div>
501<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]502 <p>
503 This pass is a simple post-dominator construction algorithm for finding
504 post-dominators.
505 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]506</div>
507
508<!-------------------------------------------------------------------------- -->
509<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]510 <a name="print-alias-sets">Alias Set Printer</a>
511</div>
512<div class="doc_text">
513 <p>Yet to be written.</p>
514</div>
515
516<!-------------------------------------------------------------------------- -->
517<div class="doc_subsection">
518 <a name="print-callgraph">Print a call graph</a>
519</div>
520<div class="doc_text">
521 <p>
522 This pass, only available in <code>opt</code>, prints the call graph to
523 standard output in a human-readable form.
524 </p>
525</div>
526
527<!-------------------------------------------------------------------------- -->
528<div class="doc_subsection">
529 <a name="print-callgraph-sccs">Print SCCs of the Call Graph</a>
530</div>
531<div class="doc_text">
532 <p>
533 This pass, only available in <code>opt</code>, prints the SCCs of the call
534 graph to standard output in a human-readable form.
535 </p>
536</div>
537
538<!-------------------------------------------------------------------------- -->
539<div class="doc_subsection">
540 <a name="print-cfg-sccs">Print SCCs of each function CFG</a>
541</div>
542<div class="doc_text">
543 <p>
544 This pass, only available in <code>opt</code>, prints the SCCs of each
545 function CFG to standard output in a human-readable form.
546 </p>
547</div>
548
549<!-------------------------------------------------------------------------- -->
550<div class="doc_subsection">
551 <a name="print-externalfnconstants">Print external fn callsites passed constants</a>
552</div>
553<div class="doc_text">
554 <p>
555 This pass, only available in <code>opt</code>, prints out call sites to
556 external functions that are called with constant arguments. This can be
557 useful when looking for standard library functions we should constant fold
558 or handle in alias analyses.
559 </p>
560</div>
561
562<!-------------------------------------------------------------------------- -->
563<div class="doc_subsection">
564 <a name="print-function">Print function to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]565</div>
566<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]567 <p>
568 The <code>PrintFunctionPass</code> class is designed to be pipelined with
569 other <code>FunctionPass</code>es, and prints out the functions of the module
570 as they are processed.
571 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]572</div>
573
574<!-------------------------------------------------------------------------- -->
575<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]576 <a name="print-module">Print module to stderr</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]577</div>
578<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]579 <p>
580 This pass simply prints out the entire module when it is executed.
581 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]582</div>
583
584<!-------------------------------------------------------------------------- -->
585<div class="doc_subsection">
Duncan Sands3ee8fc92008-09-23 12:47:39 +0000[diff] [blame]586 <a name="print-used-types">Find Used Types</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]587</div>
588<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]589 <p>
590 This pass is used to seek out all of the types in use by the program. Note
591 that this analysis explicitly does not include types only used by the symbol
592 table.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]593</div>
594
595<!-------------------------------------------------------------------------- -->
596<div class="doc_subsection">
597 <a name="profile-loader">Load profile information from llvmprof.out</a>
598</div>
599<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]600 <p>
601 A concrete implementation of profiling information that loads the information
602 from a profile dump file.
603 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]604</div>
605
606<!-------------------------------------------------------------------------- -->
607<div class="doc_subsection">
608 <a name="scalar-evolution">Scalar Evolution Analysis</a>
609</div>
610<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]611 <p>
612 The <code>ScalarEvolution</code> analysis can be used to analyze and
613 catagorize scalar expressions in loops. It specializes in recognizing general
614 induction variables, representing them with the abstract and opaque
615 <code>SCEV</code> class. Given this analysis, trip counts of loops and other
616 important properties can be obtained.
617 </p>
618
619 <p>
620 This analysis is primarily useful for induction variable substitution and
621 strength reduction.
622 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]623</div>
624
625<!-------------------------------------------------------------------------- -->
626<div class="doc_subsection">
627 <a name="targetdata">Target Data Layout</a>
628</div>
629<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]630 <p>Provides other passes access to information on how the size and alignment
631 required by the the target ABI for various data types.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]632</div>
633
634<!-- ======================================================================= -->
635<div class="doc_section"> <a name="transform">Transform Passes</a></div>
636<div class="doc_text">
637 <p>This section describes the LLVM Transform Passes.</p>
638</div>
639
640<!-------------------------------------------------------------------------- -->
641<div class="doc_subsection">
642 <a name="adce">Aggressive Dead Code Elimination</a>
643</div>
644<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]645 <p>ADCE aggressively tries to eliminate code. This pass is similar to
646 <a href="#dce">DCE</a> but it assumes that values are dead until proven
647 otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
648 the liveness of values.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]649</div>
650
651<!-------------------------------------------------------------------------- -->
652<div class="doc_subsection">
653 <a name="argpromotion">Promote 'by reference' arguments to scalars</a>
654</div>
655<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]656 <p>
657 This pass promotes "by reference" arguments to be "by value" arguments. In
658 practice, this means looking for internal functions that have pointer
659 arguments. If it can prove, through the use of alias analysis, that an
660 argument is *only* loaded, then it can pass the value into the function
661 instead of the address of the value. This can cause recursive simplification
662 of code and lead to the elimination of allocas (especially in C++ template
663 code like the STL).
664 </p>
665
666 <p>
667 This pass also handles aggregate arguments that are passed into a function,
668 scalarizing them if the elements of the aggregate are only loaded. Note that
669 it refuses to scalarize aggregates which would require passing in more than
670 three operands to the function, because passing thousands of operands for a
671 large array or structure is unprofitable!
672 </p>
673
674 <p>
675 Note that this transformation could also be done for arguments that are only
676 stored to (returning the value instead), but does not currently. This case
677 would be best handled when and if LLVM starts supporting multiple return
678 values from functions.
679 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]680</div>
681
682<!-------------------------------------------------------------------------- -->
683<div class="doc_subsection">
684 <a name="block-placement">Profile Guided Basic Block Placement</a>
685</div>
686<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]687 <p>This pass is a very simple profile guided basic block placement algorithm.
688 The idea is to put frequently executed blocks together at the start of the
689 function and hopefully increase the number of fall-through conditional
690 branches. If there is no profile information for a particular function, this
691 pass basically orders blocks in depth-first order.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]692</div>
693
694<!-------------------------------------------------------------------------- -->
695<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]696 <a name="break-crit-edges">Break critical edges in CFG</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]697</div>
698<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]699 <p>
700 Break all of the critical edges in the CFG by inserting a dummy basic block.
701 It may be "required" by passes that cannot deal with critical edges. This
702 transformation obviously invalidates the CFG, but can update forward dominator
703 (set, immediate dominators, tree, and frontier) information.
704 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]705</div>
706
707<!-------------------------------------------------------------------------- -->
708<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]709 <a name="codegenprepare">Prepare a function for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]710</div>
711<div class="doc_text">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]712 This pass munges the code in the input function to better prepare it for
713 SelectionDAG-based code generation. This works around limitations in it's
714 basic-block-at-a-time approach. It should eventually be removed.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]715</div>
716
717<!-------------------------------------------------------------------------- -->
718<div class="doc_subsection">
719 <a name="condprop">Conditional Propagation</a>
720</div>
721<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]722 <p>This pass propagates information about conditional expressions through the
723 program, allowing it to eliminate conditional branches in some cases.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]724</div>
725
726<!-------------------------------------------------------------------------- -->
727<div class="doc_subsection">
728 <a name="constmerge">Merge Duplicate Global Constants</a>
729</div>
730<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]731 <p>
732 Merges duplicate global constants together into a single constant that is
733 shared. This is useful because some passes (ie TraceValues) insert a lot of
734 string constants into the program, regardless of whether or not an existing
735 string is available.
736 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]737</div>
738
739<!-------------------------------------------------------------------------- -->
740<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]741 <a name="constprop">Simple constant propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]742</div>
743<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]744 <p>This file implements constant propagation and merging. It looks for
745 instructions involving only constant operands and replaces them with a
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]746 constant value instead of an instruction. For example:</p>
747 <blockquote><pre>add i32 1, 2</pre></blockquote>
748 <p>becomes</p>
749 <blockquote><pre>i32 3</pre></blockquote>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]750 <p>NOTE: this pass has a habit of making definitions be dead. It is a good
751 idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
752 sometime after running this pass.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]753</div>
754
755<!-------------------------------------------------------------------------- -->
756<div class="doc_subsection">
757 <a name="dce">Dead Code Elimination</a>
758</div>
759<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]760 <p>
761 Dead code elimination is similar to <a href="#die">dead instruction
762 elimination</a>, but it rechecks instructions that were used by removed
763 instructions to see if they are newly dead.
764 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]765</div>
766
767<!-------------------------------------------------------------------------- -->
768<div class="doc_subsection">
769 <a name="deadargelim">Dead Argument Elimination</a>
770</div>
771<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]772 <p>
773 This pass deletes dead arguments from internal functions. Dead argument
774 elimination removes arguments which are directly dead, as well as arguments
775 only passed into function calls as dead arguments of other functions. This
776 pass also deletes dead arguments in a similar way.
777 </p>
778
779 <p>
780 This pass is often useful as a cleanup pass to run after aggressive
781 interprocedural passes, which add possibly-dead arguments.
782 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]783</div>
784
785<!-------------------------------------------------------------------------- -->
786<div class="doc_subsection">
787 <a name="deadtypeelim">Dead Type Elimination</a>
788</div>
789<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]790 <p>
791 This pass is used to cleanup the output of GCC. It eliminate names for types
792 that are unused in the entire translation unit, using the <a
793 href="#findusedtypes">find used types</a> pass.
794 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]795</div>
796
797<!-------------------------------------------------------------------------- -->
798<div class="doc_subsection">
799 <a name="die">Dead Instruction Elimination</a>
800</div>
801<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]802 <p>
803 Dead instruction elimination performs a single pass over the function,
804 removing instructions that are obviously dead.
805 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]806</div>
807
808<!-------------------------------------------------------------------------- -->
809<div class="doc_subsection">
810 <a name="dse">Dead Store Elimination</a>
811</div>
812<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]813 <p>
814 A trivial dead store elimination that only considers basic-block local
815 redundant stores.
816 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]817</div>
818
819<!-------------------------------------------------------------------------- -->
820<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]821 <a name="globaldce">Dead Global Elimination</a>
822</div>
823<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]824 <p>
825 This transform is designed to eliminate unreachable internal globals from the
826 program. It uses an aggressive algorithm, searching out globals that are
827 known to be alive. After it finds all of the globals which are needed, it
828 deletes whatever is left over. This allows it to delete recursive chunks of
829 the program which are unreachable.
830 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]831</div>
832
833<!-------------------------------------------------------------------------- -->
834<div class="doc_subsection">
835 <a name="globalopt">Global Variable Optimizer</a>
836</div>
837<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]838 <p>
839 This pass transforms simple global variables that never have their address
840 taken. If obviously true, it marks read/write globals as constant, deletes
841 variables only stored to, etc.
842 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]843</div>
844
845<!-------------------------------------------------------------------------- -->
846<div class="doc_subsection">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]847 <a name="gvn">Global Value Numbering</a>
848</div>
849<div class="doc_text">
850 <p>
Chris Lattner60f03402009-10-10 18:40:48 +0000[diff] [blame]851 This pass performs global value numbering to eliminate fully and partially
852 redundant instructions. It also performs redundant load elimination.
Matthijs Kooijman845f5242008-06-05 07:55:49 +0000[diff] [blame]853 </p>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]854</div>
855
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]856
857<!-------------------------------------------------------------------------- -->
858<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]859 <a name="indmemrem">Indirect Malloc and Free Removal</a>
860</div>
861<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]862 <p>
863 This pass finds places where memory allocation functions may escape into
864 indirect land. Some transforms are much easier (aka possible) only if free
865 or malloc are not called indirectly.
866 </p>
867
868 <p>
869 Thus find places where the address of memory functions are taken and construct
870 bounce functions with direct calls of those functions.
871 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]872</div>
873
874<!-------------------------------------------------------------------------- -->
875<div class="doc_subsection">
876 <a name="indvars">Canonicalize Induction Variables</a>
877</div>
878<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]879 <p>
880 This transformation analyzes and transforms the induction variables (and
881 computations derived from them) into simpler forms suitable for subsequent
882 analysis and transformation.
883 </p>
884
885 <p>
886 This transformation makes the following changes to each loop with an
887 identifiable induction variable:
888 </p>
889
890 <ol>
891 <li>All loops are transformed to have a <em>single</em> canonical
892 induction variable which starts at zero and steps by one.</li>
893 <li>The canonical induction variable is guaranteed to be the first PHI node
894 in the loop header block.</li>
895 <li>Any pointer arithmetic recurrences are raised to use array
896 subscripts.</li>
897 </ol>
898
899 <p>
900 If the trip count of a loop is computable, this pass also makes the following
901 changes:
902 </p>
903
904 <ol>
905 <li>The exit condition for the loop is canonicalized to compare the
906 induction value against the exit value. This turns loops like:
907 <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
908 into
909 <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
910 <li>Any use outside of the loop of an expression derived from the indvar
911 is changed to compute the derived value outside of the loop, eliminating
912 the dependence on the exit value of the induction variable. If the only
913 purpose of the loop is to compute the exit value of some derived
914 expression, this transformation will make the loop dead.</li>
Gordon Henriksene626bbe2007-11-04 16:17:00 +0000[diff] [blame]915 </ol>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]916
917 <p>
918 This transformation should be followed by strength reduction after all of the
919 desired loop transformations have been performed. Additionally, on targets
920 where it is profitable, the loop could be transformed to count down to zero
921 (the "do loop" optimization).
922 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]923</div>
924
925<!-------------------------------------------------------------------------- -->
926<div class="doc_subsection">
927 <a name="inline">Function Integration/Inlining</a>
928</div>
929<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]930 <p>
931 Bottom-up inlining of functions into callees.
932 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]933</div>
934
935<!-------------------------------------------------------------------------- -->
936<div class="doc_subsection">
937 <a name="insert-block-profiling">Insert instrumentation for block profiling</a>
938</div>
939<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]940 <p>
941 This pass instruments the specified program with counters for basic block
942 profiling, which counts the number of times each basic block executes. This
943 is the most basic form of profiling, which can tell which blocks are hot, but
944 cannot reliably detect hot paths through the CFG.
945 </p>
946
947 <p>
948 Note that this implementation is very naïve. Control equivalent regions of
949 the CFG should not require duplicate counters, but it does put duplicate
950 counters in.
951 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]952</div>
953
954<!-------------------------------------------------------------------------- -->
955<div class="doc_subsection">
956 <a name="insert-edge-profiling">Insert instrumentation for edge profiling</a>
957</div>
958<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]959 <p>
960 This pass instruments the specified program with counters for edge profiling.
961 Edge profiling can give a reasonable approximation of the hot paths through a
962 program, and is used for a wide variety of program transformations.
963 </p>
964
965 <p>
966 Note that this implementation is very naïve. It inserts a counter for
967 <em>every</em> edge in the program, instead of using control flow information
968 to prune the number of counters inserted.
969 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]970</div>
971
972<!-------------------------------------------------------------------------- -->
973<div class="doc_subsection">
974 <a name="insert-function-profiling">Insert instrumentation for function profiling</a>
975</div>
976<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]977 <p>
978 This pass instruments the specified program with counters for function
979 profiling, which counts the number of times each function is called.
980 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]981</div>
982
983<!-------------------------------------------------------------------------- -->
984<div class="doc_subsection">
985 <a name="insert-null-profiling-rs">Measure profiling framework overhead</a>
986</div>
987<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]988 <p>
989 The basic profiler that does nothing. It is the default profiler and thus
990 terminates <code>RSProfiler</code> chains. It is useful for measuring
991 framework overhead.
992 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]993</div>
994
995<!-------------------------------------------------------------------------- -->
996<div class="doc_subsection">
997 <a name="insert-rs-profiling-framework">Insert random sampling instrumentation framework</a>
998</div>
999<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1000 <p>
1001 The second stage of the random-sampling instrumentation framework, duplicates
1002 all instructions in a function, ignoring the profiling code, then connects the
1003 two versions together at the entry and at backedges. At each connection point
1004 a choice is made as to whether to jump to the profiled code (take a sample) or
1005 execute the unprofiled code.
1006 </p>
1007
1008 <p>
1009 After this pass, it is highly recommended to run<a href="#mem2reg">mem2reg</a>
1010 and <a href="#adce">adce</a>. <a href="#instcombine">instcombine</a>,
1011 <a href="#load-vn">load-vn</a>, <a href="#gdce">gdce</a>, and
1012 <a href="#dse">dse</a> also are good to run afterwards.
1013 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1014</div>
1015
1016<!-------------------------------------------------------------------------- -->
1017<div class="doc_subsection">
1018 <a name="instcombine">Combine redundant instructions</a>
1019</div>
1020<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1021 <p>
1022 Combine instructions to form fewer, simple
1023 instructions. This pass does not modify the CFG This pass is where algebraic
1024 simplification happens.
1025 </p>
1026
1027 <p>
1028 This pass combines things like:
1029 </p>
1030
1031<blockquote><pre
1032>%Y = add i32 %X, 1
1033%Z = add i32 %Y, 1</pre></blockquote>
1034
1035 <p>
1036 into:
1037 </p>
1038
1039<blockquote><pre
1040>%Z = add i32 %X, 2</pre></blockquote>
1041
1042 <p>
1043 This is a simple worklist driven algorithm.
1044 </p>
1045
1046 <p>
1047 This pass guarantees that the following canonicalizations are performed on
1048 the program:
1049 </p>
1050
1051 <ul>
1052 <li>If a binary operator has a constant operand, it is moved to the right-
1053 hand side.</li>
1054 <li>Bitwise operators with constant operands are always grouped so that
1055 shifts are performed first, then <code>or</code>s, then
1056 <code>and</code>s, then <code>xor</code>s.</li>
1057 <li>Compare instructions are converted from <code>&lt;</code>,
1058 <code>&gt;</code>, <code>≤</code>, or <code>≥</code> to
1059 <code>=</code> or <code>≠</code> if possible.</li>
1060 <li>All <code>cmp</code> instructions on boolean values are replaced with
1061 logical operations.</li>
1062 <li><code>add <var>X</var>, <var>X</var></code> is represented as
1063 <code>mul <var>X</var>, 2</code> ⇒ <code>shl <var>X</var>, 1</code></li>
1064 <li>Multiplies with a constant power-of-two argument are transformed into
1065 shifts.</li>
1066 <li>… etc.</li>
1067 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1068</div>
1069
1070<!-------------------------------------------------------------------------- -->
1071<div class="doc_subsection">
1072 <a name="internalize">Internalize Global Symbols</a>
1073</div>
1074<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1075 <p>
1076 This pass loops over all of the functions in the input module, looking for a
1077 main function. If a main function is found, all other functions and all
1078 global variables with initializers are marked as internal.
1079 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1080</div>
1081
1082<!-------------------------------------------------------------------------- -->
1083<div class="doc_subsection">
1084 <a name="ipconstprop">Interprocedural constant propagation</a>
1085</div>
1086<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1087 <p>
1088 This pass implements an <em>extremely</em> simple interprocedural constant
1089 propagation pass. It could certainly be improved in many different ways,
1090 like using a worklist. This pass makes arguments dead, but does not remove
1091 them. The existing dead argument elimination pass should be run after this
1092 to clean up the mess.
1093 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1094</div>
1095
1096<!-------------------------------------------------------------------------- -->
1097<div class="doc_subsection">
1098 <a name="ipsccp">Interprocedural Sparse Conditional Constant Propagation</a>
1099</div>
1100<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1101 <p>
1102 An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
1103 Propagation</a>.
1104 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1105</div>
1106
1107<!-------------------------------------------------------------------------- -->
1108<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1109 <a name="jump-threading">Thread control through conditional blocks</a>
1110</div>
1111<div class="doc_text">
1112 <p>
1113 Jump threading tries to find distinct threads of control flow running through
1114 a basic block. This pass looks at blocks that have multiple predecessors and
1115 multiple successors. If one or more of the predecessors of the block can be
1116 proven to always cause a jump to one of the successors, we forward the edge
1117 from the predecessor to the successor by duplicating the contents of this
1118 block.
1119 </p>
1120 <p>
1121 An example of when this can occur is code like this:
1122 </p>
1123
1124 <pre
1125>if () { ...
1126 X = 4;
1127}
1128if (X &lt; 3) {</pre>
1129
1130 <p>
1131 In this case, the unconditional branch at the end of the first if can be
1132 revectored to the false side of the second if.
1133 </p>
1134</div>
1135
1136<!-------------------------------------------------------------------------- -->
1137<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1138 <a name="lcssa">Loop-Closed SSA Form Pass</a>
1139</div>
1140<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1141 <p>
1142 This pass transforms loops by placing phi nodes at the end of the loops for
1143 all values that are live across the loop boundary. For example, it turns
1144 the left into the right code:
1145 </p>
1146
1147 <pre
1148>for (...) for (...)
1149 if (c) if (c)
1150 X1 = ... X1 = ...
1151 else else
1152 X2 = ... X2 = ...
1153 X3 = phi(X1, X2) X3 = phi(X1, X2)
1154... = X3 + 4 X4 = phi(X3)
1155 ... = X4 + 4</pre>
1156
1157 <p>
1158 This is still valid LLVM; the extra phi nodes are purely redundant, and will
1159 be trivially eliminated by <code>InstCombine</code>. The major benefit of
1160 this transformation is that it makes many other loop optimizations, such as
1161 LoopUnswitching, simpler.
1162 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1163</div>
1164
1165<!-------------------------------------------------------------------------- -->
1166<div class="doc_subsection">
1167 <a name="licm">Loop Invariant Code Motion</a>
1168</div>
1169<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1170 <p>
1171 This pass performs loop invariant code motion, attempting to remove as much
1172 code from the body of a loop as possible. It does this by either hoisting
1173 code into the preheader block, or by sinking code to the exit blocks if it is
1174 safe. This pass also promotes must-aliased memory locations in the loop to
1175 live in registers, thus hoisting and sinking "invariant" loads and stores.
1176 </p>
1177
1178 <p>
1179 This pass uses alias analysis for two purposes:
1180 </p>
1181
1182 <ul>
1183 <li>Moving loop invariant loads and calls out of loops. If we can determine
1184 that a load or call inside of a loop never aliases anything stored to,
1185 we can hoist it or sink it like any other instruction.</li>
1186 <li>Scalar Promotion of Memory - If there is a store instruction inside of
1187 the loop, we try to move the store to happen AFTER the loop instead of
1188 inside of the loop. This can only happen if a few conditions are true:
1189 <ul>
1190 <li>The pointer stored through is loop invariant.</li>
1191 <li>There are no stores or loads in the loop which <em>may</em> alias
1192 the pointer. There are no calls in the loop which mod/ref the
1193 pointer.</li>
1194 </ul>
1195 If these conditions are true, we can promote the loads and stores in the
1196 loop of the pointer to use a temporary alloca'd variable. We then use
1197 the mem2reg functionality to construct the appropriate SSA form for the
1198 variable.</li>
1199 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1200</div>
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1201<!-------------------------------------------------------------------------- -->
1202<div class="doc_subsection">
1203 <a name="loop-deletion">Dead Loop Deletion Pass</a>
1204</div>
1205<div class="doc_text">
1206 <p>
1207 This file implements the Dead Loop Deletion Pass. This pass is responsible
1208 for eliminating loops with non-infinite computable trip counts that have no
1209 side effects or volatile instructions, and do not contribute to the
1210 computation of the function's return value.
1211 </p>
1212</div>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1213
1214<!-------------------------------------------------------------------------- -->
1215<div class="doc_subsection">
1216 <a name="loop-extract">Extract loops into new functions</a>
1217</div>
1218<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1219 <p>
1220 A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
1221 extract each top-level loop into its own new function. If the loop is the
1222 <em>only</em> loop in a given function, it is not touched. This is a pass most
1223 useful for debugging via bugpoint.
1224 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1225</div>
1226
1227<!-------------------------------------------------------------------------- -->
1228<div class="doc_subsection">
1229 <a name="loop-extract-single">Extract at most one loop into a new function</a>
1230</div>
1231<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1232 <p>
1233 Similar to <a href="#loop-extract">Extract loops into new functions</a>,
1234 this pass extracts one natural loop from the program into a function if it
1235 can. This is used by bugpoint.
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-index-split">Index Split Loops</a>
1242</div>
1243<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1244 <p>
1245 This pass divides loop's iteration range by spliting loop such that each
1246 individual loop is executed efficiently.
1247 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1248</div>
1249
1250<!-------------------------------------------------------------------------- -->
1251<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1252 <a name="loop-reduce">Loop Strength Reduction</a>
1253</div>
1254<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1255 <p>
1256 This pass performs a strength reduction on array references inside loops that
1257 have as one or more of their components the loop induction variable. This is
1258 accomplished by creating a new value to hold the initial value of the array
1259 access for the first iteration, and then creating a new GEP instruction in
1260 the loop to increment the value by the appropriate amount.
1261 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1262</div>
1263
1264<!-------------------------------------------------------------------------- -->
1265<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1266 <a name="loop-rotate">Rotate Loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1267</div>
1268<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1269 <p>A simple loop rotation transformation.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1270</div>
1271
1272<!-------------------------------------------------------------------------- -->
1273<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1274 <a name="loop-unroll">Unroll loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1275</div>
1276<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1277 <p>
1278 This pass implements a simple loop unroller. It works best when loops have
1279 been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
1280 allowing it to determine the trip counts of loops easily.
1281 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1282</div>
1283
1284<!-------------------------------------------------------------------------- -->
1285<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1286 <a name="loop-unswitch">Unswitch loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1287</div>
1288<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1289 <p>
1290 This pass transforms loops that contain branches on loop-invariant conditions
1291 to have multiple loops. For example, it turns the left into the right code:
1292 </p>
1293
1294 <pre
1295>for (...) if (lic)
1296 A for (...)
1297 if (lic) A; B; C
1298 B else
1299 C for (...)
1300 A; C</pre>
1301
1302 <p>
1303 This can increase the size of the code exponentially (doubling it every time
1304 a loop is unswitched) so we only unswitch if the resultant code will be
1305 smaller than a threshold.
1306 </p>
1307
1308 <p>
1309 This pass expects LICM to be run before it to hoist invariant conditions out
1310 of the loop, to make the unswitching opportunity obvious.
1311 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1312</div>
1313
1314<!-------------------------------------------------------------------------- -->
1315<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1316 <a name="loopsimplify">Canonicalize natural loops</a>
1317</div>
1318<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1319 <p>
1320 This pass performs several transformations to transform natural loops into a
1321 simpler form, which makes subsequent analyses and transformations simpler and
1322 more effective.
1323 </p>
1324
1325 <p>
1326 Loop pre-header insertion guarantees that there is a single, non-critical
1327 entry edge from outside of the loop to the loop header. This simplifies a
1328 number of analyses and transformations, such as LICM.
1329 </p>
1330
1331 <p>
1332 Loop exit-block insertion guarantees that all exit blocks from the loop
1333 (blocks which are outside of the loop that have predecessors inside of the
1334 loop) only have predecessors from inside of the loop (and are thus dominated
1335 by the loop header). This simplifies transformations such as store-sinking
1336 that are built into LICM.
1337 </p>
1338
1339 <p>
1340 This pass also guarantees that loops will have exactly one backedge.
1341 </p>
1342
1343 <p>
1344 Note that the simplifycfg pass will clean up blocks which are split out but
1345 end up being unnecessary, so usage of this pass should not pessimize
1346 generated code.
1347 </p>
1348
1349 <p>
1350 This pass obviously modifies the CFG, but updates loop information and
1351 dominator information.
1352 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1353</div>
1354
1355<!-------------------------------------------------------------------------- -->
1356<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1357 <a name="lowerallocs">Lower allocations from instructions to calls</a>
1358</div>
1359<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1360 <p>
1361 Turn <tt>malloc</tt> and <tt>free</tt> instructions into <tt>@malloc</tt> and
1362 <tt>@free</tt> calls.
1363 </p>
1364
1365 <p>
1366 This is a target-dependent tranformation because it depends on the size of
1367 data types and alignment constraints.
1368 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1369</div>
1370
1371<!-------------------------------------------------------------------------- -->
1372<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1373 <a name="lowerinvoke">Lower invoke and unwind, for unwindless code generators</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1374</div>
1375<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1376 <p>
1377 This transformation is designed for use by code generators which do not yet
1378 support stack unwinding. This pass supports two models of exception handling
1379 lowering, the 'cheap' support and the 'expensive' support.
1380 </p>
1381
1382 <p>
1383 'Cheap' exception handling support gives the program the ability to execute
1384 any program which does not "throw an exception", by turning 'invoke'
1385 instructions into calls and by turning 'unwind' instructions into calls to
1386 abort(). If the program does dynamically use the unwind instruction, the
1387 program will print a message then abort.
1388 </p>
1389
1390 <p>
1391 'Expensive' exception handling support gives the full exception handling
1392 support to the program at the cost of making the 'invoke' instruction
1393 really expensive. It basically inserts setjmp/longjmp calls to emulate the
1394 exception handling as necessary.
1395 </p>
1396
1397 <p>
1398 Because the 'expensive' support slows down programs a lot, and EH is only
1399 used for a subset of the programs, it must be specifically enabled by the
1400 <tt>-enable-correct-eh-support</tt> option.
1401 </p>
1402
1403 <p>
1404 Note that after this pass runs the CFG is not entirely accurate (exceptional
1405 control flow edges are not correct anymore) so only very simple things should
1406 be done after the lowerinvoke pass has run (like generation of native code).
1407 This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
1408 support the invoke instruction yet" lowering pass.
1409 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1410</div>
1411
1412<!-------------------------------------------------------------------------- -->
1413<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1414 <a name="lowersetjmp">Lower Set Jump</a>
1415</div>
1416<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1417 <p>
1418 Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
1419 instructions as necessary.
1420 </p>
1421
1422 <p>
1423 Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
1424 call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
1425 This unwinds the stack for us calling all of the destructors for
1426 objects allocated on the stack.
1427 </p>
1428
1429 <p>
1430 At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
1431 removed. The calls in a function that have a <tt>setjmp</tt> are converted to
1432 invoke where the except part checks to see if it's a <tt>longjmp</tt>
1433 exception and, if so, if it's handled in the function. If it is, then it gets
1434 the value returned by the <tt>longjmp</tt> and goes to where the basic block
1435 was split. <tt>invoke</tt> instructions are handled in a similar fashion with
1436 the original except block being executed if it isn't a <tt>longjmp</tt>
1437 except that is handled by that function.
1438 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1439</div>
1440
1441<!-------------------------------------------------------------------------- -->
1442<div class="doc_subsection">
1443 <a name="lowerswitch">Lower SwitchInst's to branches</a>
1444</div>
1445<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1446 <p>
1447 Rewrites <tt>switch</tt> instructions with a sequence of branches, which
1448 allows targets to get away with not implementing the switch instruction until
1449 it is convenient.
1450 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1451</div>
1452
1453<!-------------------------------------------------------------------------- -->
1454<div class="doc_subsection">
1455 <a name="mem2reg">Promote Memory to Register</a>
1456</div>
1457<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1458 <p>
1459 This file promotes memory references to be register references. It promotes
1460 <tt>alloca</tt> instructions which only have <tt>load</tt>s and
1461 <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
1462 frontiers to place <tt>phi</tt> nodes, then traversing the function in
1463 depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
1464 appropriate. This is just the standard SSA construction algorithm to construct
1465 "pruned" SSA form.
1466 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1467</div>
1468
1469<!-------------------------------------------------------------------------- -->
1470<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1471 <a name="memcpyopt">Optimize use of memcpy and friend</a>
1472</div>
1473<div class="doc_text">
1474 <p>
1475 This pass performs various transformations related to eliminating memcpy
1476 calls, or transforming sets of stores into memset's.
1477 </p>
1478</div>
1479
1480<!-------------------------------------------------------------------------- -->
1481<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1482 <a name="mergereturn">Unify function exit nodes</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1483</div>
1484<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1485 <p>
1486 Ensure that functions have at most one <tt>ret</tt> instruction in them.
1487 Additionally, it keeps track of which node is the new exit node of the CFG.
1488 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1489</div>
1490
1491<!-------------------------------------------------------------------------- -->
1492<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1493 <a name="prune-eh">Remove unused exception handling info</a>
1494</div>
1495<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1496 <p>
1497 This file implements a simple interprocedural pass which walks the call-graph,
1498 turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
1499 only if the callee cannot throw an exception. It implements this as a
1500 bottom-up traversal of the call-graph.
1501 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1502</div>
1503
1504<!-------------------------------------------------------------------------- -->
1505<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1506 <a name="reassociate">Reassociate expressions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1507</div>
1508<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1509 <p>
1510 This pass reassociates commutative expressions in an order that is designed
1511 to promote better constant propagation, GCSE, LICM, PRE, etc.
1512 </p>
1513
1514 <p>
1515 For example: 4 + (<var>x</var> + 5) ⇒ <var>x</var> + (4 + 5)
1516 </p>
1517
1518 <p>
1519 In the implementation of this algorithm, constants are assigned rank = 0,
1520 function arguments are rank = 1, and other values are assigned ranks
1521 corresponding to the reverse post order traversal of current function
1522 (starting at 2), which effectively gives values in deep loops higher rank
1523 than values not in loops.
1524 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1525</div>
1526
1527<!-------------------------------------------------------------------------- -->
1528<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1529 <a name="reg2mem">Demote all values to stack slots</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1530</div>
1531<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1532 <p>
1533 This file demotes all registers to memory references. It is intented to be
1534 the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]1535 <tt>load</tt> instructions, the only values live across basic blocks are
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1536 <tt>alloca</tt> instructions and <tt>load</tt> instructions before
1537 <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
1538 easier. To make later hacking easier, the entry block is split into two, such
1539 that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
1540 entry block.
1541 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1542</div>
1543
1544<!-------------------------------------------------------------------------- -->
1545<div class="doc_subsection">
1546 <a name="scalarrepl">Scalar Replacement of Aggregates</a>
1547</div>
1548<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1549 <p>
1550 The well-known scalar replacement of aggregates transformation. This
1551 transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
1552 or array) into individual <tt>alloca</tt> instructions for each member if
1553 possible. Then, if possible, it transforms the individual <tt>alloca</tt>
1554 instructions into nice clean scalar SSA form.
1555 </p>
1556
1557 <p>
1558 This combines a simple scalar replacement of aggregates algorithm with the <a
1559 href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
1560 especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
1561 then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
1562 promote works well.
1563 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1564</div>
1565
1566<!-------------------------------------------------------------------------- -->
1567<div class="doc_subsection">
1568 <a name="sccp">Sparse Conditional Constant Propagation</a>
1569</div>
1570<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1571 <p>
1572 Sparse conditional constant propagation and merging, which can be summarized
1573 as:
1574 </p>
1575
1576 <ol>
1577 <li>Assumes values are constant unless proven otherwise</li>
1578 <li>Assumes BasicBlocks are dead unless proven otherwise</li>
1579 <li>Proves values to be constant, and replaces them with constants</li>
1580 <li>Proves conditional branches to be unconditional</li>
1581 </ol>
1582
1583 <p>
1584 Note that this pass has a habit of making definitions be dead. It is a good
1585 idea to to run a DCE pass sometime after running this pass.
1586 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1587</div>
1588
1589<!-------------------------------------------------------------------------- -->
1590<div class="doc_subsection">
1591 <a name="simplify-libcalls">Simplify well-known library calls</a>
1592</div>
1593<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1594 <p>
1595 Applies a variety of small optimizations for calls to specific well-known
1596 function calls (e.g. runtime library functions). For example, a call
1597 <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
1598 transformed into simply <tt>return 3</tt>.
1599 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1600</div>
1601
1602<!-------------------------------------------------------------------------- -->
1603<div class="doc_subsection">
1604 <a name="simplifycfg">Simplify the CFG</a>
1605</div>
1606<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1607 <p>
1608 Performs dead code elimination and basic block merging. Specifically:
1609 </p>
1610
1611 <ol>
1612 <li>Removes basic blocks with no predecessors.</li>
1613 <li>Merges a basic block into its predecessor if there is only one and the
1614 predecessor only has one successor.</li>
1615 <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
1616 <li>Eliminates a basic block that only contains an unconditional
1617 branch.</li>
1618 </ol>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1619</div>
1620
1621<!-------------------------------------------------------------------------- -->
1622<div class="doc_subsection">
1623 <a name="strip">Strip all symbols from a module</a>
1624</div>
1625<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1626 <p>
1627 Performs code stripping. This transformation can delete:
1628 </p>
1629
1630 <ol>
1631 <li>names for virtual registers</li>
1632 <li>symbols for internal globals and functions</li>
1633 <li>debug information</li>
1634 </ol>
1635
1636 <p>
1637 Note that this transformation makes code much less readable, so it should
1638 only be used in situations where the <tt>strip</tt> utility would be used,
1639 such as reducing code size or making it harder to reverse engineer code.
1640 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1641</div>
1642
1643<!-------------------------------------------------------------------------- -->
1644<div class="doc_subsection">
Gordon Henriksena8a118b2008-05-08 17:46:35 +0000[diff] [blame]1645 <a name="strip-dead-prototypes">Remove unused function declarations</a>
1646</div>
1647<div class="doc_text">
1648 <p>
1649 This pass loops over all of the functions in the input module, looking for
1650 dead declarations and removes them. Dead declarations are declarations of
1651 functions for which no implementation is available (i.e., declarations for
1652 unused library functions).
1653 </p>
1654</div>
1655
1656<!-------------------------------------------------------------------------- -->
1657<div class="doc_subsection">
1658 <a name="sretpromotion">Promote sret arguments</a>
1659</div>
1660<div class="doc_text">
1661 <p>
1662 This pass finds functions that return a struct (using a pointer to the struct
1663 as the first argument of the function, marked with the '<tt>sret</tt>' attribute) and
1664 replaces them with a new function that simply returns each of the elements of
1665 that struct (using multiple return values).
1666 </p>
1667
1668 <p>
1669 This pass works under a number of conditions:
1670 </p>
1671
1672 <ul>
1673 <li>The returned struct must not contain other structs</li>
1674 <li>The returned struct must only be used to load values from</li>
1675 <li>The placeholder struct passed in is the result of an <tt>alloca</tt></li>
1676 </ul>
1677</div>
1678
1679<!-------------------------------------------------------------------------- -->
1680<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1681 <a name="tailcallelim">Tail Call Elimination</a>
1682</div>
1683<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1684 <p>
1685 This file transforms calls of the current function (self recursion) followed
1686 by a return instruction with a branch to the entry of the function, creating
1687 a loop. This pass also implements the following extensions to the basic
1688 algorithm:
1689 </p>
1690
1691 <ul>
1692 <li>Trivial instructions between the call and return do not prevent the
1693 transformation from taking place, though currently the analysis cannot
1694 support moving any really useful instructions (only dead ones).
1695 <li>This pass transforms functions that are prevented from being tail
1696 recursive by an associative expression to use an accumulator variable,
1697 thus compiling the typical naive factorial or <tt>fib</tt> implementation
1698 into efficient code.
1699 <li>TRE is performed if the function returns void, if the return
1700 returns the result returned by the call, or if the function returns a
1701 run-time constant on all exits from the function. It is possible, though
1702 unlikely, that the return returns something else (like constant 0), and
1703 can still be TRE'd. It can be TRE'd if <em>all other</em> return
1704 instructions in the function return the exact same value.
1705 <li>If it can prove that callees do not access theier caller stack frame,
1706 they are marked as eligible for tail call elimination (by the code
1707 generator).
1708 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1709</div>
1710
1711<!-------------------------------------------------------------------------- -->
1712<div class="doc_subsection">
1713 <a name="tailduplicate">Tail Duplication</a>
1714</div>
1715<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1716 <p>
1717 This pass performs a limited form of tail duplication, intended to simplify
1718 CFGs by removing some unconditional branches. This pass is necessary to
1719 straighten out loops created by the C front-end, but also is capable of
1720 making other code nicer. After this pass is run, the CFG simplify pass
1721 should be run to clean up the mess.
1722 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1723</div>
1724
1725<!-- ======================================================================= -->
1726<div class="doc_section"> <a name="transform">Utility Passes</a></div>
1727<div class="doc_text">
1728 <p>This section describes the LLVM Utility Passes.</p>
1729</div>
1730
1731<!-------------------------------------------------------------------------- -->
1732<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1733 <a name="deadarghaX0r">Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1734</div>
1735<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1736 <p>
1737 Same as dead argument elimination, but deletes arguments to functions which
1738 are external. This is only for use by <a
1739 href="Bugpoint.html">bugpoint</a>.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1740</div>
1741
1742<!-------------------------------------------------------------------------- -->
1743<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1744 <a name="extract-blocks">Extract Basic Blocks From Module (for bugpoint use)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1745</div>
1746<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1747 <p>
1748 This pass is used by bugpoint to extract all blocks from the module into their
1749 own functions.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1750</div>
1751
1752<!-------------------------------------------------------------------------- -->
1753<div class="doc_subsection">
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]1754 <a name="preverify">Preliminary module verification</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1755</div>
1756<div class="doc_text">
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame]1757 <p>
1758 Ensures that the module is in the form required by the <a
1759 href="#verifier">Module Verifier</a> pass.
1760 </p>
1761
1762 <p>
1763 Running the verifier runs this pass automatically, so there should be no need
1764 to use it directly.
1765 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1766</div>
1767
1768<!-------------------------------------------------------------------------- -->
1769<div class="doc_subsection">
1770 <a name="verify">Module Verifier</a>
1771</div>
1772<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1773 <p>
1774 Verifies an LLVM IR code. This is useful to run after an optimization which is
1775 undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
1776 emitting bitcode, and also that malformed bitcode is likely to make LLVM
1777 crash. All language front-ends are therefore encouraged to verify their output
1778 before performing optimizing transformations.
1779 </p>
1780
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1781 <ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1782 <li>Both of a binary operator's parameters are of the same type.</li>
1783 <li>Verify that the indices of mem access instructions match other
1784 operands.</li>
1785 <li>Verify that arithmetic and other things are only performed on
1786 first-class types. Verify that shifts and logicals only happen on
1787 integrals f.e.</li>
1788 <li>All of the constants in a switch statement are of the correct type.</li>
1789 <li>The code is in valid SSA form.</li>
Chris Lattner46b3abc2009-10-28 04:47:06 +0000[diff] [blame]1790 <li>It is illegal to put a label into any other type (like a structure) or
1791 to return one.</li>
Nick Lewycky0c78ac12008-03-28 06:46:51 +0000[diff] [blame]1792 <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]1793 invalid.</li>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1794 <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
1795 <li>PHI nodes must be the first thing in a basic block, all grouped
1796 together.</li>
1797 <li>PHI nodes must have at least one entry.</li>
1798 <li>All basic blocks should only end with terminator insts, not contain
1799 them.</li>
1800 <li>The entry node to a function must not have predecessors.</li>
1801 <li>All Instructions must be embedded into a basic block.</li>
1802 <li>Functions cannot take a void-typed parameter.</li>
1803 <li>Verify that a function's argument list agrees with its declared
1804 type.</li>
1805 <li>It is illegal to specify a name for a void value.</li>
1806 <li>It is illegal to have a internal global value with no initializer.</li>
1807 <li>It is illegal to have a ret instruction that returns a value that does
1808 not agree with the function return value type.</li>
1809 <li>Function call argument types match the function prototype.</li>
1810 <li>All other things that are tested by asserts spread about the code.</li>
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1811 </ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1812
1813 <p>
1814 Note that this does not provide full security verification (like Java), but
1815 instead just tries to ensure that code is well-formed.
1816 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1817</div>
1818
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1819<!-------------------------------------------------------------------------- -->
1820<div class="doc_subsection">
1821 <a name="view-cfg">View CFG of function</a>
1822</div>
1823<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1824 <p>
1825 Displays the control flow graph using the GraphViz tool.
1826 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1827</div>
1828
1829<!-------------------------------------------------------------------------- -->
1830<div class="doc_subsection">
1831 <a name="view-cfg-only">View CFG of function (with no function bodies)</a>
1832</div>
1833<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1834 <p>
1835 Displays the control flow graph using the GraphViz tool, but omitting function
1836 bodies.
1837 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1838</div>
1839
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1840<!-- *********************************************************************** -->
1841
1842<hr>
1843<address>
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Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]1845 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
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Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1848
1849 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
1850 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
1851 Last modified: $Date$
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1853
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