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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>
81<tr><td><a href="#basicvn">-basicvn</a></td><td>Basic Value Numbering (default GVN impl)</td></tr>
82<tr><td><a href="#callgraph">-callgraph</a></td><td>Print a call graph</td></tr>
83<tr><td><a href="#callscc">-callscc</a></td><td>Print SCCs of the Call Graph</td></tr>
84<tr><td><a href="#cfgscc">-cfgscc</a></td><td>Print SCCs of each function CFG</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]85<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]86<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
87<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
88<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]89<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]90<tr><td><a href="#externalfnconstants">-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
91<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]92<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
93<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
94<tr><td><a href="#load-vn">-load-vn</a></td><td>Load Value Numbering</td></tr>
95<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Construction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]96<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]97<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
98<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
99<tr><td><a href="#postdomfrontier">-postdomfrontier</a></td><td>Post-Dominance Frontier Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]100<tr><td><a href="#postdomtree">-postdomtree</a></td><td>Post-Dominator Tree Construction</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]101<tr><td><a href="#print">-print</a></td><td>Print function to stderr</td></tr>
102<tr><td><a href="#print-alias-sets">-print-alias-sets</a></td><td>Alias Set Printer</td></tr>
103<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
104<tr><td><a href="#print-cfg">-print-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
105<tr><td><a href="#print-cfg-only">-print-cfg-only</a></td><td>Print CFG of function to 'dot' file (with no function bodies)</td></tr>
106<tr><td><a href="#printm">-printm</a></td><td>Print module to stderr</td></tr>
107<tr><td><a href="#printusedtypes">-printusedtypes</a></td><td>Find Used Types</td></tr>
108<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
109<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
110<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
111
112
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]113<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
114<tr><th>Option</th><th>Name</th></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]115<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
116<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
117<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]118<tr><td><a href="#break-crit-edges">-break-crit-edges</a></td><td>Break critical edges in CFG</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]119<tr><td><a href="#cee">-cee</a></td><td>Correlated Expression Elimination</td></tr>
120<tr><td><a href="#condprop">-condprop</a></td><td>Conditional Propagation</td></tr>
121<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
122<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
123<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
124<tr><td><a href="#deadargelim">-deadargelim</a></td><td>Dead Argument Elimination</td></tr>
125<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
126<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
127<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
128<tr><td><a href="#gcse">-gcse</a></td><td>Global Common Subexpression Elimination</td></tr>
129<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
130<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]131<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]132<tr><td><a href="#gvnpre">-gvnpre</a></td><td>Global Value Numbering/Partial Redundancy Elimination</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]133<tr><td><a href="#indmemrem">-indmemrem</a></td><td>Indirect Malloc and Free Removal</td></tr>
134<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
135<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
136<tr><td><a href="#insert-block-profiling">-insert-block-profiling</a></td><td>Insert instrumentation for block profiling</td></tr>
137<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
138<tr><td><a href="#insert-function-profiling">-insert-function-profiling</a></td><td>Insert instrumentation for function profiling</td></tr>
139<tr><td><a href="#insert-null-profiling-rs">-insert-null-profiling-rs</a></td><td>Measure profiling framework overhead</td></tr>
140<tr><td><a href="#insert-rs-profiling-framework">-insert-rs-profiling-framework</a></td><td>Insert random sampling instrumentation framework</td></tr>
141<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
142<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
143<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
144<tr><td><a href="#ipsccp">-ipsccp</a></td><td>Interprocedural Sparse Conditional Constant Propagation</td></tr>
145<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
146<tr><td><a href="#licm">-licm</a></td><td>Loop Invariant Code Motion</td></tr>
147<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
148<tr><td><a href="#loop-extract-single">-loop-extract-single</a></td><td>Extract at most one loop into a new function</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]149<tr><td><a href="#loop-index-split">-loop-index-split</a></td><td>Index Split Loops</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]150<tr><td><a href="#loop-reduce">-loop-reduce</a></td><td>Loop Strength Reduction</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]151<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
152<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
153<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
154<tr><td><a href="#loopsimplify">-loopsimplify</a></td><td>Canonicalize natural loops</td></tr>
155<tr><td><a href="#lower-packed">-lower-packed</a></td><td>lowers packed operations to operations on smaller packed datatypes</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]156<tr><td><a href="#lowerallocs">-lowerallocs</a></td><td>Lower allocations from instructions to calls</td></tr>
157<tr><td><a href="#lowergc">-lowergc</a></td><td>Lower GC intrinsics, for GCless code generators</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]158<tr><td><a href="#lowerinvoke">-lowerinvoke</a></td><td>Lower invoke and unwind, for unwindless code generators</td></tr>
159<tr><td><a href="#lowerselect">-lowerselect</a></td><td>Lower select instructions to branches</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]160<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
161<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
162<tr><td><a href="#mem2reg">-mem2reg</a></td><td>Promote Memory to Register</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]163<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]164<tr><td><a href="#predsimplify">-predsimplify</a></td><td>Predicate Simplifier</td></tr>
165<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
166<tr><td><a href="#raiseallocs">-raiseallocs</a></td><td>Raise allocations from calls to instructions</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]167<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
168<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]169<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates</td></tr>
170<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
171<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
172<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
173<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
174<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
175<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]176
177
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]178<tr><th colspan="2"><b>UTILITY PASSES</b></th></tr>
179<tr><th>Option</th><th>Name</th></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]180<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
181<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^]182<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]183<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]184<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
185<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]186</table>
187</div>
188
189<!-- ======================================================================= -->
190<div class="doc_section"> <a name="example">Analysis Passes</a></div>
191<div class="doc_text">
192 <p>This section describes the LLVM Analysis Passes.</p>
193</div>
194
195<!-------------------------------------------------------------------------- -->
196<div class="doc_subsection">
197 <a name="aa-eval">Exhaustive Alias Analysis Precision Evaluator</a>
198</div>
199<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]200 <p>This is a simple N^2 alias analysis accuracy evaluator.
201 Basically, for each function in the program, it simply queries to see how the
202 alias analysis implementation answers alias queries between each pair of
203 pointers in the function.</p>
204
205 <p>This is inspired and adapted from code by: Naveen Neelakantam, Francesco
206 Spadini, and Wojciech Stryjewski.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]207</div>
208
209<!-------------------------------------------------------------------------- -->
210<div class="doc_subsection">
211 <a name="anders-aa">Andersen's Interprocedural Alias Analysis</a>
212</div>
213<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]214 <p>
215 This is an implementation of Andersen's interprocedural alias
216 analysis
217 </p>
218
219 <p>
220 In pointer analysis terms, this is a subset-based, flow-insensitive,
221 field-sensitive, and context-insensitive algorithm pointer algorithm.
222 </p>
223
224 <p>
225 This algorithm is implemented as three stages:
226 </p>
227
228 <ol>
229 <li>Object identification.</li>
230 <li>Inclusion constraint identification.</li>
231 <li>Offline constraint graph optimization.</li>
232 <li>Inclusion constraint solving.</li>
233 </ol>
234
235 <p>
236 The object identification stage identifies all of the memory objects in the
237 program, which includes globals, heap allocated objects, and stack allocated
238 objects.
239 </p>
240
241 <p>
242 The inclusion constraint identification stage finds all inclusion constraints
243 in the program by scanning the program, looking for pointer assignments and
244 other statements that effect the points-to graph. For a statement like
245 <code><var>A</var> = <var>B</var></code>, this statement is processed to
246 indicate that <var>A</var> can point to anything that <var>B</var> can point
247 to. Constraints can handle copies, loads, and stores, and address taking.
248 </p>
249
250 <p>
251 The offline constraint graph optimization portion includes offline variable
252 substitution algorithms intended to computer pointer and location
253 equivalences. Pointer equivalences are those pointers that will have the
254 same points-to sets, and location equivalences are those variables that
255 always appear together in points-to sets.
256 </p>
257
258 <p>
259 The inclusion constraint solving phase iteratively propagates the inclusion
260 constraints until a fixed point is reached. This is an O(<var>n</var>³)
261 algorithm.
262 </p>
263
264 <p>
265 Function constraints are handled as if they were structs with <var>X</var>
266 fields. Thus, an access to argument <var>X</var> of function <var>Y</var> is
267 an access to node index <code>getNode(<var>Y</var>) + <var>X</var></code>.
268 This representation allows handling of indirect calls without any issues. To
269 wit, an indirect call <code><var>Y</var>(<var>a</var>,<var>b</var>)</code> is
270 equivalent to <code>*(<var>Y</var> + 1) = <var>a</var>, *(<var>Y</var> + 2) =
271 <var>b</var></code>. The return node for a function <var>F</var> is always
272 located at <code>getNode(<var>F</var>) + CallReturnPos</code>. The arguments
273 start at <code>getNode(<var>F</var>) + CallArgPos</code>.
274 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]275</div>
276
277<!-------------------------------------------------------------------------- -->
278<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]279 <a name="basicaa">Basic Alias Analysis (default AA impl)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]280</div>
281<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]282 <p>
283 This is the default implementation of the Alias Analysis interface
284 that simply implements a few identities (two different globals cannot alias,
285 etc), but otherwise does no analysis.
286 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]287</div>
288
289<!-------------------------------------------------------------------------- -->
290<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]291 <a name="basiccg">Basic CallGraph Construction</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]292</div>
293<div class="doc_text">
294 <p>Yet to be written.</p>
295</div>
296
297<!-------------------------------------------------------------------------- -->
298<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]299 <a name="basicvn">Basic Value Numbering (default GVN impl)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]300</div>
301<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]302 <p>
303 This is the default implementation of the <code>ValueNumbering</code>
304 interface. It walks the SSA def-use chains to trivially identify
305 lexically identical expressions. This does not require any ahead of time
306 analysis, so it is a very fast default implementation.
307 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]308</div>
309
310<!-------------------------------------------------------------------------- -->
311<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]312 <a name="callgraph">Print a call graph</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]313</div>
314<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]315 <p>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]316 This pass, only available in <code>opt</code>, prints the call graph to
317 standard output in a human-readable form.
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]318 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]319</div>
320
321<!-------------------------------------------------------------------------- -->
322<div class="doc_subsection">
323 <a name="callscc">Print SCCs of the Call Graph</a>
324</div>
325<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]326 <p>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]327 This pass, only available in <code>opt</code>, prints the SCCs of the call
328 graph to standard output in a human-readable form.
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]329 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]330</div>
331
332<!-------------------------------------------------------------------------- -->
333<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]334 <a name="cfgscc">Print SCCs of each function CFG</a>
335</div>
336<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]337 <p>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]338 This pass, only available in <code>opt</code>, prints the SCCs of each
339 function CFG to standard output in a human-readable form.
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]340 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]341</div>
342
343<!-------------------------------------------------------------------------- -->
344<div class="doc_subsection">
345 <a name="codegenprepare">Optimize for code generation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]346</div>
347<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]348 <p>
349 This pass munges the code in the input function to better prepare it for
350 SelectionDAG-based code generation. This works around limitations in it's
351 basic-block-at-a-time approach. It should eventually be removed.
352 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]353</div>
354
355<!-------------------------------------------------------------------------- -->
356<div class="doc_subsection">
357 <a name="count-aa">Count Alias Analysis Query Responses</a>
358</div>
359<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]360 <p>
361 A pass which can be used to count how many alias queries
362 are being made and how the alias analysis implementation being used responds.
363 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]364</div>
365
366<!-------------------------------------------------------------------------- -->
367<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]368 <a name="debug-aa">AA use debugger</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]369</div>
370<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]371 <p>
372 This simple pass checks alias analysis users to ensure that if they
373 create a new value, they do not query AA without informing it of the value.
374 It acts as a shim over any other AA pass you want.
375 </p>
376
377 <p>
378 Yes keeping track of every value in the program is expensive, but this is
379 a debugging pass.
380 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]381</div>
382
383<!-------------------------------------------------------------------------- -->
384<div class="doc_subsection">
385 <a name="domfrontier">Dominance Frontier Construction</a>
386</div>
387<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]388 <p>
389 This pass is a simple dominator construction algorithm for finding forward
390 dominator frontiers.
391 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]392</div>
393
394<!-------------------------------------------------------------------------- -->
395<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]396 <a name="domtree">Dominator Tree Construction</a>
397</div>
398<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]399 <p>
400 This pass is a simple dominator construction algorithm for finding forward
401 dominators.
402 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]403</div>
404
405<!-------------------------------------------------------------------------- -->
406<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]407 <a name="externalfnconstants">Print external fn callsites passed constants</a>
408</div>
409<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]410 <p>
411 This pass, only available in <code>opt</code>, prints out call sites to
412 external functions that are called with constant arguments. This can be
413 useful when looking for standard library functions we should constant fold
414 or handle in alias analyses.
415 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]416</div>
417
418<!-------------------------------------------------------------------------- -->
419<div class="doc_subsection">
420 <a name="globalsmodref-aa">Simple mod/ref analysis for globals</a>
421</div>
422<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]423 <p>
424 This simple pass provides alias and mod/ref information for global values
425 that do not have their address taken, and keeps track of whether functions
426 read or write memory (are "pure"). For this simple (but very common) case,
427 we can provide pretty accurate and useful information.
428 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]429</div>
430
431<!-------------------------------------------------------------------------- -->
432<div class="doc_subsection">
433 <a name="instcount">Counts the various types of Instructions</a>
434</div>
435<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]436 <p>
437 This pass collects the count of all instructions and reports them
438 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]439</div>
440
441<!-------------------------------------------------------------------------- -->
442<div class="doc_subsection">
443 <a name="intervals">Interval Partition Construction</a>
444</div>
445<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]446 <p>
447 This analysis calculates and represents the interval partition of a function,
448 or a preexisting interval partition.
449 </p>
450
451 <p>
452 In this way, the interval partition may be used to reduce a flow graph down
453 to its degenerate single node interval partition (unless it is irreducible).
454 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]455</div>
456
457<!-------------------------------------------------------------------------- -->
458<div class="doc_subsection">
459 <a name="load-vn">Load Value Numbering</a>
460</div>
461<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]462 <p>
463 This pass value numbers load and call instructions. To do this, it finds
464 lexically identical load instructions, and uses alias analysis to determine
465 which loads are guaranteed to produce the same value. To value number call
466 instructions, it looks for calls to functions that do not write to memory
467 which do not have intervening instructions that clobber the memory that is
468 read from.
469 </p>
470
471 <p>
472 This pass builds off of another value numbering pass to implement value
473 numbering for non-load and non-call instructions. It uses Alias Analysis so
474 that it can disambiguate the load instructions. The more powerful these base
475 analyses are, the more powerful the resultant value numbering will be.
476 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]477</div>
478
479<!-------------------------------------------------------------------------- -->
480<div class="doc_subsection">
481 <a name="loops">Natural Loop Construction</a>
482</div>
483<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]484 <p>
485 This analysis is used to identify natural loops and determine the loop depth
486 of various nodes of the CFG. Note that the loops identified may actually be
487 several natural loops that share the same header node... not just a single
488 natural loop.
489 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]490</div>
491
492<!-------------------------------------------------------------------------- -->
493<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]494 <a name="memdep">Memory Dependence Analysis</a>
495</div>
496<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]497 <p>
498 An analysis that determines, for a given memory operation, what preceding
499 memory operations it depends on. It builds on alias analysis information, and
500 tries to provide a lazy, caching interface to a common kind of alias
501 information query.
502 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]503</div>
504
505<!-------------------------------------------------------------------------- -->
506<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]507 <a name="no-aa">No Alias Analysis (always returns 'may' alias)</a>
508</div>
509<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]510 <p>
511 Always returns "I don't know" for alias queries. NoAA is unlike other alias
512 analysis implementations, in that it does not chain to a previous analysis. As
513 such it doesn't follow many of the rules that other alias analyses must.
514 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]515</div>
516
517<!-------------------------------------------------------------------------- -->
518<div class="doc_subsection">
519 <a name="no-profile">No Profile Information</a>
520</div>
521<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]522 <p>
523 The default "no profile" implementation of the abstract
524 <code>ProfileInfo</code> interface.
525 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]526</div>
527
528<!-------------------------------------------------------------------------- -->
529<div class="doc_subsection">
530 <a name="postdomfrontier">Post-Dominance Frontier Construction</a>
531</div>
532<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]533 <p>
534 This pass is a simple post-dominator construction algorithm for finding
535 post-dominator frontiers.
536 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]537</div>
538
539<!-------------------------------------------------------------------------- -->
540<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]541 <a name="postdomtree">Post-Dominator Tree Construction</a>
542</div>
543<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]544 <p>
545 This pass is a simple post-dominator construction algorithm for finding
546 post-dominators.
547 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]548</div>
549
550<!-------------------------------------------------------------------------- -->
551<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]552 <a name="print">Print function to stderr</a>
553</div>
554<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]555 <p>
556 The <code>PrintFunctionPass</code> class is designed to be pipelined with
557 other <code>FunctionPass</code>es, and prints out the functions of the module
558 as they are processed.
559 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]560</div>
561
562<!-------------------------------------------------------------------------- -->
563<div class="doc_subsection">
564 <a name="print-alias-sets">Alias Set Printer</a>
565</div>
566<div class="doc_text">
567 <p>Yet to be written.</p>
568</div>
569
570<!-------------------------------------------------------------------------- -->
571<div class="doc_subsection">
572 <a name="print-callgraph">Print Call Graph to 'dot' file</a>
573</div>
574<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]575 <p>
576 This pass, only available in <code>opt</code>, prints the call graph into a
577 <code>.dot</code> graph. This graph can then be processed with the "dot" tool
578 to convert it to postscript or some other suitable format.
579 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]580</div>
581
582<!-------------------------------------------------------------------------- -->
583<div class="doc_subsection">
584 <a name="print-cfg">Print CFG of function to 'dot' file</a>
585</div>
586<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]587 <p>
588 This pass, only available in <code>opt</code>, prints the control flow graph
589 into a <code>.dot</code> graph. This graph can then be processed with the
590 "dot" tool to convert it to postscript or some other suitable format.
591 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]592</div>
593
594<!-------------------------------------------------------------------------- -->
595<div class="doc_subsection">
596 <a name="print-cfg-only">Print CFG of function to 'dot' file (with no function bodies)</a>
597</div>
598<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]599 <p>
600 This pass, only available in <code>opt</code>, prints the control flow graph
601 into a <code>.dot</code> graph, omitting the function bodies. This graph can
602 then be processed with the "dot" tool to convert it to postscript or some
603 other suitable format.
604 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]605</div>
606
607<!-------------------------------------------------------------------------- -->
608<div class="doc_subsection">
609 <a name="printm">Print module to stderr</a>
610</div>
611<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]612 <p>
613 This pass simply prints out the entire module when it is executed.
614 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]615</div>
616
617<!-------------------------------------------------------------------------- -->
618<div class="doc_subsection">
619 <a name="printusedtypes">Find Used Types</a>
620</div>
621<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]622 <p>
623 This pass is used to seek out all of the types in use by the program. Note
624 that this analysis explicitly does not include types only used by the symbol
625 table.
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]626</div>
627
628<!-------------------------------------------------------------------------- -->
629<div class="doc_subsection">
630 <a name="profile-loader">Load profile information from llvmprof.out</a>
631</div>
632<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]633 <p>
634 A concrete implementation of profiling information that loads the information
635 from a profile dump file.
636 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]637</div>
638
639<!-------------------------------------------------------------------------- -->
640<div class="doc_subsection">
641 <a name="scalar-evolution">Scalar Evolution Analysis</a>
642</div>
643<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]644 <p>
645 The <code>ScalarEvolution</code> analysis can be used to analyze and
646 catagorize scalar expressions in loops. It specializes in recognizing general
647 induction variables, representing them with the abstract and opaque
648 <code>SCEV</code> class. Given this analysis, trip counts of loops and other
649 important properties can be obtained.
650 </p>
651
652 <p>
653 This analysis is primarily useful for induction variable substitution and
654 strength reduction.
655 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]656</div>
657
658<!-------------------------------------------------------------------------- -->
659<div class="doc_subsection">
660 <a name="targetdata">Target Data Layout</a>
661</div>
662<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]663 <p>Provides other passes access to information on how the size and alignment
664 required by the the target ABI for various data types.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]665</div>
666
667<!-- ======================================================================= -->
668<div class="doc_section"> <a name="transform">Transform Passes</a></div>
669<div class="doc_text">
670 <p>This section describes the LLVM Transform Passes.</p>
671</div>
672
673<!-------------------------------------------------------------------------- -->
674<div class="doc_subsection">
675 <a name="adce">Aggressive Dead Code Elimination</a>
676</div>
677<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]678 <p>ADCE aggressively tries to eliminate code. This pass is similar to
679 <a href="#dce">DCE</a> but it assumes that values are dead until proven
680 otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
681 the liveness of values.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]682</div>
683
684<!-------------------------------------------------------------------------- -->
685<div class="doc_subsection">
686 <a name="argpromotion">Promote 'by reference' arguments to scalars</a>
687</div>
688<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]689 <p>
690 This pass promotes "by reference" arguments to be "by value" arguments. In
691 practice, this means looking for internal functions that have pointer
692 arguments. If it can prove, through the use of alias analysis, that an
693 argument is *only* loaded, then it can pass the value into the function
694 instead of the address of the value. This can cause recursive simplification
695 of code and lead to the elimination of allocas (especially in C++ template
696 code like the STL).
697 </p>
698
699 <p>
700 This pass also handles aggregate arguments that are passed into a function,
701 scalarizing them if the elements of the aggregate are only loaded. Note that
702 it refuses to scalarize aggregates which would require passing in more than
703 three operands to the function, because passing thousands of operands for a
704 large array or structure is unprofitable!
705 </p>
706
707 <p>
708 Note that this transformation could also be done for arguments that are only
709 stored to (returning the value instead), but does not currently. This case
710 would be best handled when and if LLVM starts supporting multiple return
711 values from functions.
712 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]713</div>
714
715<!-------------------------------------------------------------------------- -->
716<div class="doc_subsection">
717 <a name="block-placement">Profile Guided Basic Block Placement</a>
718</div>
719<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]720 <p>This pass is a very simple profile guided basic block placement algorithm.
721 The idea is to put frequently executed blocks together at the start of the
722 function and hopefully increase the number of fall-through conditional
723 branches. If there is no profile information for a particular function, this
724 pass basically orders blocks in depth-first order.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]725</div>
726
727<!-------------------------------------------------------------------------- -->
728<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]729 <a name="break-crit-edges">Break critical edges in CFG</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]730</div>
731<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]732 <p>
733 Break all of the critical edges in the CFG by inserting a dummy basic block.
734 It may be "required" by passes that cannot deal with critical edges. This
735 transformation obviously invalidates the CFG, but can update forward dominator
736 (set, immediate dominators, tree, and frontier) information.
737 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]738</div>
739
740<!-------------------------------------------------------------------------- -->
741<div class="doc_subsection">
742 <a name="cee">Correlated Expression Elimination</a>
743</div>
744<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]745 <p>Correlated Expression Elimination propagates information from conditional
746 branches to blocks dominated by destinations of the branch. It propagates
747 information from the condition check itself into the body of the branch,
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]748 allowing transformations like these for example:</p>
749
750<blockquote><pre>
751if (i == 7)
752 ... 4*i; // constant propagation
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]753
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]754M = i+1; N = j+1;
755if (i == j)
756 X = M-N; // = M-M == 0;
757</pre></blockquote>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]758
759 <p>This is called Correlated Expression Elimination because we eliminate or
760 simplify expressions that are correlated with the direction of a branch. In
761 this way we use static information to give us some information about the
762 dynamic value of a variable.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]763</div>
764
765<!-------------------------------------------------------------------------- -->
766<div class="doc_subsection">
767 <a name="condprop">Conditional Propagation</a>
768</div>
769<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]770 <p>This pass propagates information about conditional expressions through the
771 program, allowing it to eliminate conditional branches in some cases.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]772</div>
773
774<!-------------------------------------------------------------------------- -->
775<div class="doc_subsection">
776 <a name="constmerge">Merge Duplicate Global Constants</a>
777</div>
778<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]779 <p>
780 Merges duplicate global constants together into a single constant that is
781 shared. This is useful because some passes (ie TraceValues) insert a lot of
782 string constants into the program, regardless of whether or not an existing
783 string is available.
784 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]785</div>
786
787<!-------------------------------------------------------------------------- -->
788<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]789 <a name="constprop">Simple constant propagation</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]790</div>
791<div class="doc_text">
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]792 <p>This file implements constant propagation and merging. It looks for
793 instructions involving only constant operands and replaces them with a
Gordon Henriksenddaa61d2007-10-25 08:58:56 +0000[diff] [blame]794 constant value instead of an instruction. For example:</p>
795 <blockquote><pre>add i32 1, 2</pre></blockquote>
796 <p>becomes</p>
797 <blockquote><pre>i32 3</pre></blockquote>
Reid Spenceraf4af3a2007-03-27 02:49:31 +0000[diff] [blame]798 <p>NOTE: this pass has a habit of making definitions be dead. It is a good
799 idea to to run a <a href="#die">DIE</a> (Dead Instruction Elimination) pass
800 sometime after running this pass.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]801</div>
802
803<!-------------------------------------------------------------------------- -->
804<div class="doc_subsection">
805 <a name="dce">Dead Code Elimination</a>
806</div>
807<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]808 <p>
809 Dead code elimination is similar to <a href="#die">dead instruction
810 elimination</a>, but it rechecks instructions that were used by removed
811 instructions to see if they are newly dead.
812 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]813</div>
814
815<!-------------------------------------------------------------------------- -->
816<div class="doc_subsection">
817 <a name="deadargelim">Dead Argument Elimination</a>
818</div>
819<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]820 <p>
821 This pass deletes dead arguments from internal functions. Dead argument
822 elimination removes arguments which are directly dead, as well as arguments
823 only passed into function calls as dead arguments of other functions. This
824 pass also deletes dead arguments in a similar way.
825 </p>
826
827 <p>
828 This pass is often useful as a cleanup pass to run after aggressive
829 interprocedural passes, which add possibly-dead arguments.
830 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]831</div>
832
833<!-------------------------------------------------------------------------- -->
834<div class="doc_subsection">
835 <a name="deadtypeelim">Dead Type Elimination</a>
836</div>
837<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]838 <p>
839 This pass is used to cleanup the output of GCC. It eliminate names for types
840 that are unused in the entire translation unit, using the <a
841 href="#findusedtypes">find used types</a> pass.
842 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]843</div>
844
845<!-------------------------------------------------------------------------- -->
846<div class="doc_subsection">
847 <a name="die">Dead Instruction Elimination</a>
848</div>
849<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]850 <p>
851 Dead instruction elimination performs a single pass over the function,
852 removing instructions that are obviously dead.
853 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]854</div>
855
856<!-------------------------------------------------------------------------- -->
857<div class="doc_subsection">
858 <a name="dse">Dead Store Elimination</a>
859</div>
860<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]861 <p>
862 A trivial dead store elimination that only considers basic-block local
863 redundant stores.
864 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]865</div>
866
867<!-------------------------------------------------------------------------- -->
868<div class="doc_subsection">
869 <a name="gcse">Global Common Subexpression Elimination</a>
870</div>
871<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]872 <p>
873 This pass is designed to be a very quick global transformation that
874 eliminates global common subexpressions from a function. It does this by
875 using an existing value numbering implementation to identify the common
876 subexpressions, eliminating them when possible.
877 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]878</div>
879
880<!-------------------------------------------------------------------------- -->
881<div class="doc_subsection">
882 <a name="globaldce">Dead Global Elimination</a>
883</div>
884<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]885 <p>
886 This transform is designed to eliminate unreachable internal globals from the
887 program. It uses an aggressive algorithm, searching out globals that are
888 known to be alive. After it finds all of the globals which are needed, it
889 deletes whatever is left over. This allows it to delete recursive chunks of
890 the program which are unreachable.
891 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]892</div>
893
894<!-------------------------------------------------------------------------- -->
895<div class="doc_subsection">
896 <a name="globalopt">Global Variable Optimizer</a>
897</div>
898<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]899 <p>
900 This pass transforms simple global variables that never have their address
901 taken. If obviously true, it marks read/write globals as constant, deletes
902 variables only stored to, etc.
903 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]904</div>
905
906<!-------------------------------------------------------------------------- -->
907<div class="doc_subsection">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]908 <a name="gvn">Global Value Numbering</a>
909</div>
910<div class="doc_text">
911 <p>
912 This pass performs global value numbering to eliminate fully redundant
913 instructions. It also performs simple dead load elimination.
914 </p>
915</div>
916
917<!-------------------------------------------------------------------------- -->
918<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]919 <a name="gvnpre">Global Value Numbering/Partial Redundancy Elimination</a>
920</div>
921<div class="doc_text">
Gordon Henriksen0e15dc22007-10-25 10:18:27 +0000[diff] [blame]922 <p>
923 This pass performs a hybrid of global value numbering and partial redundancy
924 elimination, known as GVN-PRE. It performs partial redundancy elimination on
925 values, rather than lexical expressions, allowing a more comprehensive view
926 the optimization. It replaces redundant values with uses of earlier
927 occurences of the same value. While this is beneficial in that it eliminates
928 unneeded computation, it also increases register pressure by creating large
929 live ranges, and should be used with caution on platforms that are very
930 sensitive to register pressure.
931 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]932</div>
933
934<!-------------------------------------------------------------------------- -->
935<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]936 <a name="indmemrem">Indirect Malloc and Free Removal</a>
937</div>
938<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]939 <p>
940 This pass finds places where memory allocation functions may escape into
941 indirect land. Some transforms are much easier (aka possible) only if free
942 or malloc are not called indirectly.
943 </p>
944
945 <p>
946 Thus find places where the address of memory functions are taken and construct
947 bounce functions with direct calls of those functions.
948 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]949</div>
950
951<!-------------------------------------------------------------------------- -->
952<div class="doc_subsection">
953 <a name="indvars">Canonicalize Induction Variables</a>
954</div>
955<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]956 <p>
957 This transformation analyzes and transforms the induction variables (and
958 computations derived from them) into simpler forms suitable for subsequent
959 analysis and transformation.
960 </p>
961
962 <p>
963 This transformation makes the following changes to each loop with an
964 identifiable induction variable:
965 </p>
966
967 <ol>
968 <li>All loops are transformed to have a <em>single</em> canonical
969 induction variable which starts at zero and steps by one.</li>
970 <li>The canonical induction variable is guaranteed to be the first PHI node
971 in the loop header block.</li>
972 <li>Any pointer arithmetic recurrences are raised to use array
973 subscripts.</li>
974 </ol>
975
976 <p>
977 If the trip count of a loop is computable, this pass also makes the following
978 changes:
979 </p>
980
981 <ol>
982 <li>The exit condition for the loop is canonicalized to compare the
983 induction value against the exit value. This turns loops like:
984 <blockquote><pre>for (i = 7; i*i < 1000; ++i)</pre></blockquote>
985 into
986 <blockquote><pre>for (i = 0; i != 25; ++i)</pre></blockquote></li>
987 <li>Any use outside of the loop of an expression derived from the indvar
988 is changed to compute the derived value outside of the loop, eliminating
989 the dependence on the exit value of the induction variable. If the only
990 purpose of the loop is to compute the exit value of some derived
991 expression, this transformation will make the loop dead.</li>
Gordon Henriksene626bbe2007-11-04 16:17:00 +0000[diff] [blame]992 </ol>
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]993
994 <p>
995 This transformation should be followed by strength reduction after all of the
996 desired loop transformations have been performed. Additionally, on targets
997 where it is profitable, the loop could be transformed to count down to zero
998 (the "do loop" optimization).
999 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1000</div>
1001
1002<!-------------------------------------------------------------------------- -->
1003<div class="doc_subsection">
1004 <a name="inline">Function Integration/Inlining</a>
1005</div>
1006<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1007 <p>
1008 Bottom-up inlining of functions into callees.
1009 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1010</div>
1011
1012<!-------------------------------------------------------------------------- -->
1013<div class="doc_subsection">
1014 <a name="insert-block-profiling">Insert instrumentation for block profiling</a>
1015</div>
1016<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1017 <p>
1018 This pass instruments the specified program with counters for basic block
1019 profiling, which counts the number of times each basic block executes. This
1020 is the most basic form of profiling, which can tell which blocks are hot, but
1021 cannot reliably detect hot paths through the CFG.
1022 </p>
1023
1024 <p>
1025 Note that this implementation is very naïve. Control equivalent regions of
1026 the CFG should not require duplicate counters, but it does put duplicate
1027 counters in.
1028 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1029</div>
1030
1031<!-------------------------------------------------------------------------- -->
1032<div class="doc_subsection">
1033 <a name="insert-edge-profiling">Insert instrumentation for edge profiling</a>
1034</div>
1035<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1036 <p>
1037 This pass instruments the specified program with counters for edge profiling.
1038 Edge profiling can give a reasonable approximation of the hot paths through a
1039 program, and is used for a wide variety of program transformations.
1040 </p>
1041
1042 <p>
1043 Note that this implementation is very naïve. It inserts a counter for
1044 <em>every</em> edge in the program, instead of using control flow information
1045 to prune the number of counters inserted.
1046 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1047</div>
1048
1049<!-------------------------------------------------------------------------- -->
1050<div class="doc_subsection">
1051 <a name="insert-function-profiling">Insert instrumentation for function profiling</a>
1052</div>
1053<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1054 <p>
1055 This pass instruments the specified program with counters for function
1056 profiling, which counts the number of times each function is called.
1057 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1058</div>
1059
1060<!-------------------------------------------------------------------------- -->
1061<div class="doc_subsection">
1062 <a name="insert-null-profiling-rs">Measure profiling framework overhead</a>
1063</div>
1064<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1065 <p>
1066 The basic profiler that does nothing. It is the default profiler and thus
1067 terminates <code>RSProfiler</code> chains. It is useful for measuring
1068 framework overhead.
1069 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1070</div>
1071
1072<!-------------------------------------------------------------------------- -->
1073<div class="doc_subsection">
1074 <a name="insert-rs-profiling-framework">Insert random sampling instrumentation framework</a>
1075</div>
1076<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1077 <p>
1078 The second stage of the random-sampling instrumentation framework, duplicates
1079 all instructions in a function, ignoring the profiling code, then connects the
1080 two versions together at the entry and at backedges. At each connection point
1081 a choice is made as to whether to jump to the profiled code (take a sample) or
1082 execute the unprofiled code.
1083 </p>
1084
1085 <p>
1086 After this pass, it is highly recommended to run<a href="#mem2reg">mem2reg</a>
1087 and <a href="#adce">adce</a>. <a href="#instcombine">instcombine</a>,
1088 <a href="#load-vn">load-vn</a>, <a href="#gdce">gdce</a>, and
1089 <a href="#dse">dse</a> also are good to run afterwards.
1090 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1091</div>
1092
1093<!-------------------------------------------------------------------------- -->
1094<div class="doc_subsection">
1095 <a name="instcombine">Combine redundant instructions</a>
1096</div>
1097<div class="doc_text">
Gordon Henriksen55cbec32007-10-26 03:03:51 +0000[diff] [blame]1098 <p>
1099 Combine instructions to form fewer, simple
1100 instructions. This pass does not modify the CFG This pass is where algebraic
1101 simplification happens.
1102 </p>
1103
1104 <p>
1105 This pass combines things like:
1106 </p>
1107
1108<blockquote><pre
1109>%Y = add i32 %X, 1
1110%Z = add i32 %Y, 1</pre></blockquote>
1111
1112 <p>
1113 into:
1114 </p>
1115
1116<blockquote><pre
1117>%Z = add i32 %X, 2</pre></blockquote>
1118
1119 <p>
1120 This is a simple worklist driven algorithm.
1121 </p>
1122
1123 <p>
1124 This pass guarantees that the following canonicalizations are performed on
1125 the program:
1126 </p>
1127
1128 <ul>
1129 <li>If a binary operator has a constant operand, it is moved to the right-
1130 hand side.</li>
1131 <li>Bitwise operators with constant operands are always grouped so that
1132 shifts are performed first, then <code>or</code>s, then
1133 <code>and</code>s, then <code>xor</code>s.</li>
1134 <li>Compare instructions are converted from <code>&lt;</code>,
1135 <code>&gt;</code>, <code>≤</code>, or <code>≥</code> to
1136 <code>=</code> or <code>≠</code> if possible.</li>
1137 <li>All <code>cmp</code> instructions on boolean values are replaced with
1138 logical operations.</li>
1139 <li><code>add <var>X</var>, <var>X</var></code> is represented as
1140 <code>mul <var>X</var>, 2</code> ⇒ <code>shl <var>X</var>, 1</code></li>
1141 <li>Multiplies with a constant power-of-two argument are transformed into
1142 shifts.</li>
1143 <li>… etc.</li>
1144 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1145</div>
1146
1147<!-------------------------------------------------------------------------- -->
1148<div class="doc_subsection">
1149 <a name="internalize">Internalize Global Symbols</a>
1150</div>
1151<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1152 <p>
1153 This pass loops over all of the functions in the input module, looking for a
1154 main function. If a main function is found, all other functions and all
1155 global variables with initializers are marked as internal.
1156 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1157</div>
1158
1159<!-------------------------------------------------------------------------- -->
1160<div class="doc_subsection">
1161 <a name="ipconstprop">Interprocedural constant propagation</a>
1162</div>
1163<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1164 <p>
1165 This pass implements an <em>extremely</em> simple interprocedural constant
1166 propagation pass. It could certainly be improved in many different ways,
1167 like using a worklist. This pass makes arguments dead, but does not remove
1168 them. The existing dead argument elimination pass should be run after this
1169 to clean up the mess.
1170 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1171</div>
1172
1173<!-------------------------------------------------------------------------- -->
1174<div class="doc_subsection">
1175 <a name="ipsccp">Interprocedural Sparse Conditional Constant Propagation</a>
1176</div>
1177<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1178 <p>
1179 An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
1180 Propagation</a>.
1181 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1182</div>
1183
1184<!-------------------------------------------------------------------------- -->
1185<div class="doc_subsection">
1186 <a name="lcssa">Loop-Closed SSA Form Pass</a>
1187</div>
1188<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1189 <p>
1190 This pass transforms loops by placing phi nodes at the end of the loops for
1191 all values that are live across the loop boundary. For example, it turns
1192 the left into the right code:
1193 </p>
1194
1195 <pre
1196>for (...) for (...)
1197 if (c) if (c)
1198 X1 = ... X1 = ...
1199 else else
1200 X2 = ... X2 = ...
1201 X3 = phi(X1, X2) X3 = phi(X1, X2)
1202... = X3 + 4 X4 = phi(X3)
1203 ... = X4 + 4</pre>
1204
1205 <p>
1206 This is still valid LLVM; the extra phi nodes are purely redundant, and will
1207 be trivially eliminated by <code>InstCombine</code>. The major benefit of
1208 this transformation is that it makes many other loop optimizations, such as
1209 LoopUnswitching, simpler.
1210 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1211</div>
1212
1213<!-------------------------------------------------------------------------- -->
1214<div class="doc_subsection">
1215 <a name="licm">Loop Invariant Code Motion</a>
1216</div>
1217<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1218 <p>
1219 This pass performs loop invariant code motion, attempting to remove as much
1220 code from the body of a loop as possible. It does this by either hoisting
1221 code into the preheader block, or by sinking code to the exit blocks if it is
1222 safe. This pass also promotes must-aliased memory locations in the loop to
1223 live in registers, thus hoisting and sinking "invariant" loads and stores.
1224 </p>
1225
1226 <p>
1227 This pass uses alias analysis for two purposes:
1228 </p>
1229
1230 <ul>
1231 <li>Moving loop invariant loads and calls out of loops. If we can determine
1232 that a load or call inside of a loop never aliases anything stored to,
1233 we can hoist it or sink it like any other instruction.</li>
1234 <li>Scalar Promotion of Memory - If there is a store instruction inside of
1235 the loop, we try to move the store to happen AFTER the loop instead of
1236 inside of the loop. This can only happen if a few conditions are true:
1237 <ul>
1238 <li>The pointer stored through is loop invariant.</li>
1239 <li>There are no stores or loads in the loop which <em>may</em> alias
1240 the pointer. There are no calls in the loop which mod/ref the
1241 pointer.</li>
1242 </ul>
1243 If these conditions are true, we can promote the loads and stores in the
1244 loop of the pointer to use a temporary alloca'd variable. We then use
1245 the mem2reg functionality to construct the appropriate SSA form for the
1246 variable.</li>
1247 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1248</div>
1249
1250<!-------------------------------------------------------------------------- -->
1251<div class="doc_subsection">
1252 <a name="loop-extract">Extract loops into new functions</a>
1253</div>
1254<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1255 <p>
1256 A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
1257 extract each top-level loop into its own new function. If the loop is the
1258 <em>only</em> loop in a given function, it is not touched. This is a pass most
1259 useful for debugging via bugpoint.
1260 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1261</div>
1262
1263<!-------------------------------------------------------------------------- -->
1264<div class="doc_subsection">
1265 <a name="loop-extract-single">Extract at most one loop into a new function</a>
1266</div>
1267<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1268 <p>
1269 Similar to <a href="#loop-extract">Extract loops into new functions</a>,
1270 this pass extracts one natural loop from the program into a function if it
1271 can. This is used by bugpoint.
1272 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1273</div>
1274
1275<!-------------------------------------------------------------------------- -->
1276<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1277 <a name="loop-index-split">Index Split Loops</a>
1278</div>
1279<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1280 <p>
1281 This pass divides loop's iteration range by spliting loop such that each
1282 individual loop is executed efficiently.
1283 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1284</div>
1285
1286<!-------------------------------------------------------------------------- -->
1287<div class="doc_subsection">
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1288 <a name="loop-reduce">Loop Strength Reduction</a>
1289</div>
1290<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1291 <p>
1292 This pass performs a strength reduction on array references inside loops that
1293 have as one or more of their components the loop induction variable. This is
1294 accomplished by creating a new value to hold the initial value of the array
1295 access for the first iteration, and then creating a new GEP instruction in
1296 the loop to increment the value by the appropriate amount.
1297 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1298</div>
1299
1300<!-------------------------------------------------------------------------- -->
1301<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1302 <a name="loop-rotate">Rotate Loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1303</div>
1304<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1305 <p>A simple loop rotation transformation.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1306</div>
1307
1308<!-------------------------------------------------------------------------- -->
1309<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1310 <a name="loop-unroll">Unroll loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1311</div>
1312<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1313 <p>
1314 This pass implements a simple loop unroller. It works best when loops have
1315 been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
1316 allowing it to determine the trip counts of loops easily.
1317 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1318</div>
1319
1320<!-------------------------------------------------------------------------- -->
1321<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1322 <a name="loop-unswitch">Unswitch loops</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1323</div>
1324<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1325 <p>
1326 This pass transforms loops that contain branches on loop-invariant conditions
1327 to have multiple loops. For example, it turns the left into the right code:
1328 </p>
1329
1330 <pre
1331>for (...) if (lic)
1332 A for (...)
1333 if (lic) A; B; C
1334 B else
1335 C for (...)
1336 A; C</pre>
1337
1338 <p>
1339 This can increase the size of the code exponentially (doubling it every time
1340 a loop is unswitched) so we only unswitch if the resultant code will be
1341 smaller than a threshold.
1342 </p>
1343
1344 <p>
1345 This pass expects LICM to be run before it to hoist invariant conditions out
1346 of the loop, to make the unswitching opportunity obvious.
1347 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1348</div>
1349
1350<!-------------------------------------------------------------------------- -->
1351<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1352 <a name="loopsimplify">Canonicalize natural loops</a>
1353</div>
1354<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1355 <p>
1356 This pass performs several transformations to transform natural loops into a
1357 simpler form, which makes subsequent analyses and transformations simpler and
1358 more effective.
1359 </p>
1360
1361 <p>
1362 Loop pre-header insertion guarantees that there is a single, non-critical
1363 entry edge from outside of the loop to the loop header. This simplifies a
1364 number of analyses and transformations, such as LICM.
1365 </p>
1366
1367 <p>
1368 Loop exit-block insertion guarantees that all exit blocks from the loop
1369 (blocks which are outside of the loop that have predecessors inside of the
1370 loop) only have predecessors from inside of the loop (and are thus dominated
1371 by the loop header). This simplifies transformations such as store-sinking
1372 that are built into LICM.
1373 </p>
1374
1375 <p>
1376 This pass also guarantees that loops will have exactly one backedge.
1377 </p>
1378
1379 <p>
1380 Note that the simplifycfg pass will clean up blocks which are split out but
1381 end up being unnecessary, so usage of this pass should not pessimize
1382 generated code.
1383 </p>
1384
1385 <p>
1386 This pass obviously modifies the CFG, but updates loop information and
1387 dominator information.
1388 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1389</div>
1390
1391<!-------------------------------------------------------------------------- -->
1392<div class="doc_subsection">
1393 <a name="lower-packed">lowers packed operations to operations on smaller packed datatypes</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1394</div>
1395<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1396 <p>
1397 Lowers operations on vector datatypes into operations on more primitive vector
1398 datatypes, and finally to scalar operations.
1399 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1400</div>
1401
1402<!-------------------------------------------------------------------------- -->
1403<div class="doc_subsection">
1404 <a name="lowerallocs">Lower allocations from instructions to calls</a>
1405</div>
1406<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1407 <p>
1408 Turn <tt>malloc</tt> and <tt>free</tt> instructions into <tt>@malloc</tt> and
1409 <tt>@free</tt> calls.
1410 </p>
1411
1412 <p>
1413 This is a target-dependent tranformation because it depends on the size of
1414 data types and alignment constraints.
1415 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1416</div>
1417
1418<!-------------------------------------------------------------------------- -->
1419<div class="doc_subsection">
1420 <a name="lowergc">Lower GC intrinsics, for GCless code generators</a>
1421</div>
1422<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1423 <p>
1424 This file implements lowering for the <tt>llvm.gc*</tt> intrinsics for targets
1425 that do not natively support them (which includes the C backend). Note that
1426 the code generated is not as efficient as it would be for targets that
1427 natively support the GC intrinsics, but it is useful for getting new targets
1428 up-and-running quickly.
1429 </p>
1430
1431 <p>
1432 This pass implements the code transformation described in this paper:
1433 </p>
1434
1435 <blockquote><p>
1436 "Accurate Garbage Collection in an Uncooperative Environment"
1437 Fergus Henderson, ISMM, 2002
1438 </p></blockquote>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1439</div>
1440
1441<!-------------------------------------------------------------------------- -->
1442<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1443 <a name="lowerinvoke">Lower invoke and unwind, for unwindless code generators</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1444</div>
1445<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1446 <p>
1447 This transformation is designed for use by code generators which do not yet
1448 support stack unwinding. This pass supports two models of exception handling
1449 lowering, the 'cheap' support and the 'expensive' support.
1450 </p>
1451
1452 <p>
1453 'Cheap' exception handling support gives the program the ability to execute
1454 any program which does not "throw an exception", by turning 'invoke'
1455 instructions into calls and by turning 'unwind' instructions into calls to
1456 abort(). If the program does dynamically use the unwind instruction, the
1457 program will print a message then abort.
1458 </p>
1459
1460 <p>
1461 'Expensive' exception handling support gives the full exception handling
1462 support to the program at the cost of making the 'invoke' instruction
1463 really expensive. It basically inserts setjmp/longjmp calls to emulate the
1464 exception handling as necessary.
1465 </p>
1466
1467 <p>
1468 Because the 'expensive' support slows down programs a lot, and EH is only
1469 used for a subset of the programs, it must be specifically enabled by the
1470 <tt>-enable-correct-eh-support</tt> option.
1471 </p>
1472
1473 <p>
1474 Note that after this pass runs the CFG is not entirely accurate (exceptional
1475 control flow edges are not correct anymore) so only very simple things should
1476 be done after the lowerinvoke pass has run (like generation of native code).
1477 This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
1478 support the invoke instruction yet" lowering pass.
1479 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1480</div>
1481
1482<!-------------------------------------------------------------------------- -->
1483<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1484 <a name="lowerselect">Lower select instructions to branches</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1485</div>
1486<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1487 <p>
1488 Lowers select instructions into conditional branches for targets that do not
1489 have conditional moves or that have not implemented the select instruction
1490 yet.
1491 </p>
1492
1493 <p>
1494 Note that this pass could be improved. In particular it turns every select
1495 instruction into a new conditional branch, even though some common cases have
1496 select instructions on the same predicate next to each other. It would be
1497 better to use the same branch for the whole group of selects.
1498 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1499</div>
1500
1501<!-------------------------------------------------------------------------- -->
1502<div class="doc_subsection">
1503 <a name="lowersetjmp">Lower Set Jump</a>
1504</div>
1505<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1506 <p>
1507 Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
1508 instructions as necessary.
1509 </p>
1510
1511 <p>
1512 Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
1513 call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
1514 This unwinds the stack for us calling all of the destructors for
1515 objects allocated on the stack.
1516 </p>
1517
1518 <p>
1519 At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
1520 removed. The calls in a function that have a <tt>setjmp</tt> are converted to
1521 invoke where the except part checks to see if it's a <tt>longjmp</tt>
1522 exception and, if so, if it's handled in the function. If it is, then it gets
1523 the value returned by the <tt>longjmp</tt> and goes to where the basic block
1524 was split. <tt>invoke</tt> instructions are handled in a similar fashion with
1525 the original except block being executed if it isn't a <tt>longjmp</tt>
1526 except that is handled by that function.
1527 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1528</div>
1529
1530<!-------------------------------------------------------------------------- -->
1531<div class="doc_subsection">
1532 <a name="lowerswitch">Lower SwitchInst's to branches</a>
1533</div>
1534<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1535 <p>
1536 Rewrites <tt>switch</tt> instructions with a sequence of branches, which
1537 allows targets to get away with not implementing the switch instruction until
1538 it is convenient.
1539 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1540</div>
1541
1542<!-------------------------------------------------------------------------- -->
1543<div class="doc_subsection">
1544 <a name="mem2reg">Promote Memory to Register</a>
1545</div>
1546<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1547 <p>
1548 This file promotes memory references to be register references. It promotes
1549 <tt>alloca</tt> instructions which only have <tt>load</tt>s and
1550 <tt>store</tt>s as uses. An <tt>alloca</tt> is transformed by using dominator
1551 frontiers to place <tt>phi</tt> nodes, then traversing the function in
1552 depth-first order to rewrite <tt>load</tt>s and <tt>store</tt>s as
1553 appropriate. This is just the standard SSA construction algorithm to construct
1554 "pruned" SSA form.
1555 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1556</div>
1557
1558<!-------------------------------------------------------------------------- -->
1559<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1560 <a name="mergereturn">Unify function exit nodes</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1561</div>
1562<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1563 <p>
1564 Ensure that functions have at most one <tt>ret</tt> instruction in them.
1565 Additionally, it keeps track of which node is the new exit node of the CFG.
1566 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1567</div>
1568
1569<!-------------------------------------------------------------------------- -->
1570<div class="doc_subsection">
1571 <a name="predsimplify">Predicate Simplifier</a>
1572</div>
1573<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1574 <p>
1575 Path-sensitive optimizer. In a branch where <tt>x == y</tt>, replace uses of
1576 <tt>x</tt> with <tt>y</tt>. Permits further optimization, such as the
1577 elimination of the unreachable call:
1578 </p>
1579
1580<blockquote><pre
1581>void test(int *p, int *q)
1582{
1583 if (p != q)
1584 return;
1585
1586 if (*p != *q)
1587 foo(); // unreachable
1588}</pre></blockquote>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1589</div>
1590
1591<!-------------------------------------------------------------------------- -->
1592<div class="doc_subsection">
1593 <a name="prune-eh">Remove unused exception handling info</a>
1594</div>
1595<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1596 <p>
1597 This file implements a simple interprocedural pass which walks the call-graph,
1598 turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
1599 only if the callee cannot throw an exception. It implements this as a
1600 bottom-up traversal of the call-graph.
1601 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1602</div>
1603
1604<!-------------------------------------------------------------------------- -->
1605<div class="doc_subsection">
1606 <a name="raiseallocs">Raise allocations from calls to instructions</a>
1607</div>
1608<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1609 <p>
1610 Converts <tt>@malloc</tt> and <tt>@free</tt> calls to <tt>malloc</tt> and
1611 <tt>free</tt> instructions.
1612 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1613</div>
1614
1615<!-------------------------------------------------------------------------- -->
1616<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1617 <a name="reassociate">Reassociate expressions</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1618</div>
1619<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1620 <p>
1621 This pass reassociates commutative expressions in an order that is designed
1622 to promote better constant propagation, GCSE, LICM, PRE, etc.
1623 </p>
1624
1625 <p>
1626 For example: 4 + (<var>x</var> + 5) ⇒ <var>x</var> + (4 + 5)
1627 </p>
1628
1629 <p>
1630 In the implementation of this algorithm, constants are assigned rank = 0,
1631 function arguments are rank = 1, and other values are assigned ranks
1632 corresponding to the reverse post order traversal of current function
1633 (starting at 2), which effectively gives values in deep loops higher rank
1634 than values not in loops.
1635 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1636</div>
1637
1638<!-------------------------------------------------------------------------- -->
1639<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1640 <a name="reg2mem">Demote all values to stack slots</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1641</div>
1642<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1643 <p>
1644 This file demotes all registers to memory references. It is intented to be
1645 the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
1646 <tt>load</tt> instructions, the only values live accross basic blocks are
1647 <tt>alloca</tt> instructions and <tt>load</tt> instructions before
1648 <tt>phi</tt> nodes. It is intended that this should make CFG hacking much
1649 easier. To make later hacking easier, the entry block is split into two, such
1650 that all introduced <tt>alloca</tt> instructions (and nothing else) are in the
1651 entry block.
1652 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1653</div>
1654
1655<!-------------------------------------------------------------------------- -->
1656<div class="doc_subsection">
1657 <a name="scalarrepl">Scalar Replacement of Aggregates</a>
1658</div>
1659<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1660 <p>
1661 The well-known scalar replacement of aggregates transformation. This
1662 transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
1663 or array) into individual <tt>alloca</tt> instructions for each member if
1664 possible. Then, if possible, it transforms the individual <tt>alloca</tt>
1665 instructions into nice clean scalar SSA form.
1666 </p>
1667
1668 <p>
1669 This combines a simple scalar replacement of aggregates algorithm with the <a
1670 href="#mem2reg"><tt>mem2reg</tt></a> algorithm because often interact,
1671 especially for C++ programs. As such, iterating between <tt>scalarrepl</tt>,
1672 then <a href="#mem2reg"><tt>mem2reg</tt></a> until we run out of things to
1673 promote works well.
1674 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1675</div>
1676
1677<!-------------------------------------------------------------------------- -->
1678<div class="doc_subsection">
1679 <a name="sccp">Sparse Conditional Constant Propagation</a>
1680</div>
1681<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1682 <p>
1683 Sparse conditional constant propagation and merging, which can be summarized
1684 as:
1685 </p>
1686
1687 <ol>
1688 <li>Assumes values are constant unless proven otherwise</li>
1689 <li>Assumes BasicBlocks are dead unless proven otherwise</li>
1690 <li>Proves values to be constant, and replaces them with constants</li>
1691 <li>Proves conditional branches to be unconditional</li>
1692 </ol>
1693
1694 <p>
1695 Note that this pass has a habit of making definitions be dead. It is a good
1696 idea to to run a DCE pass sometime after running this pass.
1697 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1698</div>
1699
1700<!-------------------------------------------------------------------------- -->
1701<div class="doc_subsection">
1702 <a name="simplify-libcalls">Simplify well-known library calls</a>
1703</div>
1704<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1705 <p>
1706 Applies a variety of small optimizations for calls to specific well-known
1707 function calls (e.g. runtime library functions). For example, a call
1708 <tt>exit(3)</tt> that occurs within the <tt>main()</tt> function can be
1709 transformed into simply <tt>return 3</tt>.
1710 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1711</div>
1712
1713<!-------------------------------------------------------------------------- -->
1714<div class="doc_subsection">
1715 <a name="simplifycfg">Simplify the CFG</a>
1716</div>
1717<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1718 <p>
1719 Performs dead code elimination and basic block merging. Specifically:
1720 </p>
1721
1722 <ol>
1723 <li>Removes basic blocks with no predecessors.</li>
1724 <li>Merges a basic block into its predecessor if there is only one and the
1725 predecessor only has one successor.</li>
1726 <li>Eliminates PHI nodes for basic blocks with a single predecessor.</li>
1727 <li>Eliminates a basic block that only contains an unconditional
1728 branch.</li>
1729 </ol>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1730</div>
1731
1732<!-------------------------------------------------------------------------- -->
1733<div class="doc_subsection">
1734 <a name="strip">Strip all symbols from a module</a>
1735</div>
1736<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1737 <p>
1738 Performs code stripping. This transformation can delete:
1739 </p>
1740
1741 <ol>
1742 <li>names for virtual registers</li>
1743 <li>symbols for internal globals and functions</li>
1744 <li>debug information</li>
1745 </ol>
1746
1747 <p>
1748 Note that this transformation makes code much less readable, so it should
1749 only be used in situations where the <tt>strip</tt> utility would be used,
1750 such as reducing code size or making it harder to reverse engineer code.
1751 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1752</div>
1753
1754<!-------------------------------------------------------------------------- -->
1755<div class="doc_subsection">
1756 <a name="tailcallelim">Tail Call Elimination</a>
1757</div>
1758<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1759 <p>
1760 This file transforms calls of the current function (self recursion) followed
1761 by a return instruction with a branch to the entry of the function, creating
1762 a loop. This pass also implements the following extensions to the basic
1763 algorithm:
1764 </p>
1765
1766 <ul>
1767 <li>Trivial instructions between the call and return do not prevent the
1768 transformation from taking place, though currently the analysis cannot
1769 support moving any really useful instructions (only dead ones).
1770 <li>This pass transforms functions that are prevented from being tail
1771 recursive by an associative expression to use an accumulator variable,
1772 thus compiling the typical naive factorial or <tt>fib</tt> implementation
1773 into efficient code.
1774 <li>TRE is performed if the function returns void, if the return
1775 returns the result returned by the call, or if the function returns a
1776 run-time constant on all exits from the function. It is possible, though
1777 unlikely, that the return returns something else (like constant 0), and
1778 can still be TRE'd. It can be TRE'd if <em>all other</em> return
1779 instructions in the function return the exact same value.
1780 <li>If it can prove that callees do not access theier caller stack frame,
1781 they are marked as eligible for tail call elimination (by the code
1782 generator).
1783 </ul>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1784</div>
1785
1786<!-------------------------------------------------------------------------- -->
1787<div class="doc_subsection">
1788 <a name="tailduplicate">Tail Duplication</a>
1789</div>
1790<div class="doc_text">
Gordon Henriksenc86b6772007-11-04 16:15:04 +0000[diff] [blame]1791 <p>
1792 This pass performs a limited form of tail duplication, intended to simplify
1793 CFGs by removing some unconditional branches. This pass is necessary to
1794 straighten out loops created by the C front-end, but also is capable of
1795 making other code nicer. After this pass is run, the CFG simplify pass
1796 should be run to clean up the mess.
1797 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1798</div>
1799
1800<!-- ======================================================================= -->
1801<div class="doc_section"> <a name="transform">Utility Passes</a></div>
1802<div class="doc_text">
1803 <p>This section describes the LLVM Utility Passes.</p>
1804</div>
1805
1806<!-------------------------------------------------------------------------- -->
1807<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1808 <a name="deadarghaX0r">Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1809</div>
1810<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1811 <p>
1812 Same as dead argument elimination, but deletes arguments to functions which
1813 are external. This is only for use by <a
1814 href="Bugpoint.html">bugpoint</a>.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1815</div>
1816
1817<!-------------------------------------------------------------------------- -->
1818<div class="doc_subsection">
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1819 <a name="extract-blocks">Extract Basic Blocks From Module (for bugpoint use)</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1820</div>
1821<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1822 <p>
1823 This pass is used by bugpoint to extract all blocks from the module into their
1824 own functions.</p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1825</div>
1826
1827<!-------------------------------------------------------------------------- -->
1828<div class="doc_subsection">
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame^]1829 <a name="preverify">Preliminary module verification</a>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1830</div>
1831<div class="doc_text">
Gordon Henriksen90a52142007-11-05 02:05:35 +0000[diff] [blame^]1832 <p>
1833 Ensures that the module is in the form required by the <a
1834 href="#verifier">Module Verifier</a> pass.
1835 </p>
1836
1837 <p>
1838 Running the verifier runs this pass automatically, so there should be no need
1839 to use it directly.
1840 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1841</div>
1842
1843<!-------------------------------------------------------------------------- -->
1844<div class="doc_subsection">
1845 <a name="verify">Module Verifier</a>
1846</div>
1847<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1848 <p>
1849 Verifies an LLVM IR code. This is useful to run after an optimization which is
1850 undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
1851 emitting bitcode, and also that malformed bitcode is likely to make LLVM
1852 crash. All language front-ends are therefore encouraged to verify their output
1853 before performing optimizing transformations.
1854 </p>
1855
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1856 <ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1857 <li>Both of a binary operator's parameters are of the same type.</li>
1858 <li>Verify that the indices of mem access instructions match other
1859 operands.</li>
1860 <li>Verify that arithmetic and other things are only performed on
1861 first-class types. Verify that shifts and logicals only happen on
1862 integrals f.e.</li>
1863 <li>All of the constants in a switch statement are of the correct type.</li>
1864 <li>The code is in valid SSA form.</li>
1865 <li>It should be illegal to put a label into any other type (like a
1866 structure) or to return one. [except constant arrays!]</li>
Gordon Henriksen873390e2007-11-04 18:17:58 +0000[diff] [blame]1867 <li>Only phi nodes can be self referential: <tt>%x = add int %x, %x</tt> is
1868 invalid.</li>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1869 <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
1870 <li>PHI nodes must be the first thing in a basic block, all grouped
1871 together.</li>
1872 <li>PHI nodes must have at least one entry.</li>
1873 <li>All basic blocks should only end with terminator insts, not contain
1874 them.</li>
1875 <li>The entry node to a function must not have predecessors.</li>
1876 <li>All Instructions must be embedded into a basic block.</li>
1877 <li>Functions cannot take a void-typed parameter.</li>
1878 <li>Verify that a function's argument list agrees with its declared
1879 type.</li>
1880 <li>It is illegal to specify a name for a void value.</li>
1881 <li>It is illegal to have a internal global value with no initializer.</li>
1882 <li>It is illegal to have a ret instruction that returns a value that does
1883 not agree with the function return value type.</li>
1884 <li>Function call argument types match the function prototype.</li>
1885 <li>All other things that are tested by asserts spread about the code.</li>
Gordon Henriksen23a8ce52007-11-04 18:14:08 +0000[diff] [blame]1886 </ul>
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1887
1888 <p>
1889 Note that this does not provide full security verification (like Java), but
1890 instead just tries to ensure that code is well-formed.
1891 </p>
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1892</div>
1893
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1894<!-------------------------------------------------------------------------- -->
1895<div class="doc_subsection">
1896 <a name="view-cfg">View CFG of function</a>
1897</div>
1898<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1899 <p>
1900 Displays the control flow graph using the GraphViz tool.
1901 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1902</div>
1903
1904<!-------------------------------------------------------------------------- -->
1905<div class="doc_subsection">
1906 <a name="view-cfg-only">View CFG of function (with no function bodies)</a>
1907</div>
1908<div class="doc_text">
Gordon Henriksen75ff18e2007-11-04 18:10:18 +0000[diff] [blame]1909 <p>
1910 Displays the control flow graph using the GraphViz tool, but omitting function
1911 bodies.
1912 </p>
Gordon Henriksen1f5cce02007-10-25 08:46:12 +0000[diff] [blame]1913</div>
1914
Reid Spencerd9aac122007-03-26 09:32:31 +0000[diff] [blame]1915<!-- *********************************************************************** -->
1916
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