my $o = $order{$1};
$o = "000" unless defined $o;
push @x, "$o<tr><td><a href=\"#$1\">-$1</a></td><td>$2</td></tr>\n";
- push @y, "$o <a name=\"$1\">$2</a>\n";
+ push @y, "$o <a name=\"$1\">-$1: $2</a>\n";
}
@x = map { s/^\d\d\d//; $_ } sort @x;
@y = map { s/^\d\d\d//; $_ } sort @y;
-->
-<div class="doc_title">LLVM's Analysis and Transform Passes</div>
+<h1>LLVM's Analysis and Transform Passes</h1>
<ol>
<li><a href="#intro">Introduction</a></li>
</div>
<!-- ======================================================================= -->
-<div class="doc_section"> <a name="intro">Introduction</a> </div>
-<div class="doc_text">
+<h2><a name="intro">Introduction</a></h2>
+<div>
<p>This document serves as a high level summary of the optimization features
that LLVM provides. Optimizations are implemented as Passes that traverse some
portion of a program to either collect information or transform the program.
bitcode are neither analysis nor transform passes.
<p>The table below provides a quick summary of each pass and links to the more
complete pass description later in the document.</p>
-</div>
-<div class="doc_text" >
+
<table>
<tr><th colspan="2"><b>ANALYSIS PASSES</b></th></tr>
<tr><th>Option</th><th>Name</th></tr>
<tr><td><a href="#aa-eval">-aa-eval</a></td><td>Exhaustive Alias Analysis Precision Evaluator</td></tr>
-<tr><td><a href="#anders-aa">-anders-aa</a></td><td>Andersen's Interprocedural Alias Analysis</td></tr>
-<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (default AA impl)</td></tr>
+<tr><td><a href="#basicaa">-basicaa</a></td><td>Basic Alias Analysis (stateless AA impl)</td></tr>
<tr><td><a href="#basiccg">-basiccg</a></td><td>Basic CallGraph Construction</td></tr>
-<tr><td><a href="#basicvn">-basicvn</a></td><td>Basic Value Numbering (default GVN impl)</td></tr>
-<tr><td><a href="#callgraph">-callgraph</a></td><td>Print a call graph</td></tr>
-<tr><td><a href="#callscc">-callscc</a></td><td>Print SCCs of the Call Graph</td></tr>
-<tr><td><a href="#cfgscc">-cfgscc</a></td><td>Print SCCs of each function CFG</td></tr>
-<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</td></tr>
<tr><td><a href="#count-aa">-count-aa</a></td><td>Count Alias Analysis Query Responses</td></tr>
<tr><td><a href="#debug-aa">-debug-aa</a></td><td>AA use debugger</td></tr>
<tr><td><a href="#domfrontier">-domfrontier</a></td><td>Dominance Frontier Construction</td></tr>
<tr><td><a href="#domtree">-domtree</a></td><td>Dominator Tree Construction</td></tr>
-<tr><td><a href="#externalfnconstants">-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
+<tr><td><a href="#dot-callgraph">-dot-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
+<tr><td><a href="#dot-cfg">-dot-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
+<tr><td><a href="#dot-cfg-only">-dot-cfg-only</a></td><td>Print CFG of function to 'dot' file (with no function bodies)</td></tr>
+<tr><td><a href="#dot-dom">-dot-dom</a></td><td>Print dominance tree of function to 'dot' file</td></tr>
+<tr><td><a href="#dot-dom-only">-dot-dom-only</a></td><td>Print dominance tree of function to 'dot' file (with no function bodies)</td></tr>
+<tr><td><a href="#dot-postdom">-dot-postdom</a></td><td>Print postdominance tree of function to 'dot' file</td></tr>
+<tr><td><a href="#dot-postdom-only">-dot-postdom-only</a></td><td>Print postdominance tree of function to 'dot' file (with no function bodies)</td></tr>
<tr><td><a href="#globalsmodref-aa">-globalsmodref-aa</a></td><td>Simple mod/ref analysis for globals</td></tr>
<tr><td><a href="#instcount">-instcount</a></td><td>Counts the various types of Instructions</td></tr>
<tr><td><a href="#intervals">-intervals</a></td><td>Interval Partition Construction</td></tr>
-<tr><td><a href="#load-vn">-load-vn</a></td><td>Load Value Numbering</td></tr>
-<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Construction</td></tr>
+<tr><td><a href="#iv-users">-iv-users</a></td><td>Induction Variable Users</td></tr>
+<tr><td><a href="#lazy-value-info">-lazy-value-info</a></td><td>Lazy Value Information Analysis</td></tr>
+<tr><td><a href="#lda">-lda</a></td><td>Loop Dependence Analysis</td></tr>
+<tr><td><a href="#libcall-aa">-libcall-aa</a></td><td>LibCall Alias Analysis</td></tr>
+<tr><td><a href="#lint">-lint</a></td><td>Statically lint-checks LLVM IR</td></tr>
+<tr><td><a href="#loops">-loops</a></td><td>Natural Loop Information</td></tr>
<tr><td><a href="#memdep">-memdep</a></td><td>Memory Dependence Analysis</td></tr>
+<tr><td><a href="#module-debuginfo">-module-debuginfo</a></td><td>Decodes module-level debug info</td></tr>
<tr><td><a href="#no-aa">-no-aa</a></td><td>No Alias Analysis (always returns 'may' alias)</td></tr>
<tr><td><a href="#no-profile">-no-profile</a></td><td>No Profile Information</td></tr>
<tr><td><a href="#postdomfrontier">-postdomfrontier</a></td><td>Post-Dominance Frontier Construction</td></tr>
<tr><td><a href="#postdomtree">-postdomtree</a></td><td>Post-Dominator Tree Construction</td></tr>
-<tr><td><a href="#print">-print</a></td><td>Print function to stderr</td></tr>
<tr><td><a href="#print-alias-sets">-print-alias-sets</a></td><td>Alias Set Printer</td></tr>
-<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print Call Graph to 'dot' file</td></tr>
-<tr><td><a href="#print-cfg">-print-cfg</a></td><td>Print CFG of function to 'dot' file</td></tr>
-<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>
-<tr><td><a href="#printm">-printm</a></td><td>Print module to stderr</td></tr>
-<tr><td><a href="#printusedtypes">-printusedtypes</a></td><td>Find Used Types</td></tr>
+<tr><td><a href="#print-callgraph">-print-callgraph</a></td><td>Print a call graph</td></tr>
+<tr><td><a href="#print-callgraph-sccs">-print-callgraph-sccs</a></td><td>Print SCCs of the Call Graph</td></tr>
+<tr><td><a href="#print-cfg-sccs">-print-cfg-sccs</a></td><td>Print SCCs of each function CFG</td></tr>
+<tr><td><a href="#print-dbginfo">-print-dbginfo</a></td><td>Print debug info in human readable form</td></tr>
+<tr><td><a href="#print-dom-info">-print-dom-info</a></td><td>Dominator Info Printer</td></tr>
+<tr><td><a href="#print-externalfnconstants">-print-externalfnconstants</a></td><td>Print external fn callsites passed constants</td></tr>
+<tr><td><a href="#print-function">-print-function</a></td><td>Print function to stderr</td></tr>
+<tr><td><a href="#print-module">-print-module</a></td><td>Print module to stderr</td></tr>
+<tr><td><a href="#print-used-types">-print-used-types</a></td><td>Find Used Types</td></tr>
+<tr><td><a href="#profile-estimator">-profile-estimator</a></td><td>Estimate profiling information</td></tr>
<tr><td><a href="#profile-loader">-profile-loader</a></td><td>Load profile information from llvmprof.out</td></tr>
+<tr><td><a href="#profile-verifier">-profile-verifier</a></td><td>Verify profiling information</td></tr>
+<tr><td><a href="#regions">-regions</a></td><td>Detect single entry single exit regions</td></tr>
<tr><td><a href="#scalar-evolution">-scalar-evolution</a></td><td>Scalar Evolution Analysis</td></tr>
+<tr><td><a href="#scev-aa">-scev-aa</a></td><td>ScalarEvolution-based Alias Analysis</td></tr>
<tr><td><a href="#targetdata">-targetdata</a></td><td>Target Data Layout</td></tr>
<tr><th colspan="2"><b>TRANSFORM PASSES</b></th></tr>
<tr><th>Option</th><th>Name</th></tr>
<tr><td><a href="#adce">-adce</a></td><td>Aggressive Dead Code Elimination</td></tr>
+<tr><td><a href="#always-inline">-always-inline</a></td><td>Inliner for always_inline functions</td></tr>
<tr><td><a href="#argpromotion">-argpromotion</a></td><td>Promote 'by reference' arguments to scalars</td></tr>
<tr><td><a href="#block-placement">-block-placement</a></td><td>Profile Guided Basic Block Placement</td></tr>
<tr><td><a href="#break-crit-edges">-break-crit-edges</a></td><td>Break critical edges in CFG</td></tr>
-<tr><td><a href="#cee">-cee</a></td><td>Correlated Expression Elimination</td></tr>
-<tr><td><a href="#condprop">-condprop</a></td><td>Conditional Propagation</td></tr>
+<tr><td><a href="#codegenprepare">-codegenprepare</a></td><td>Optimize for code generation</td></tr>
<tr><td><a href="#constmerge">-constmerge</a></td><td>Merge Duplicate Global Constants</td></tr>
<tr><td><a href="#constprop">-constprop</a></td><td>Simple constant propagation</td></tr>
<tr><td><a href="#dce">-dce</a></td><td>Dead Code Elimination</td></tr>
<tr><td><a href="#deadtypeelim">-deadtypeelim</a></td><td>Dead Type Elimination</td></tr>
<tr><td><a href="#die">-die</a></td><td>Dead Instruction Elimination</td></tr>
<tr><td><a href="#dse">-dse</a></td><td>Dead Store Elimination</td></tr>
-<tr><td><a href="#gcse">-gcse</a></td><td>Global Common Subexpression Elimination</td></tr>
+<tr><td><a href="#functionattrs">-functionattrs</a></td><td>Deduce function attributes</td></tr>
<tr><td><a href="#globaldce">-globaldce</a></td><td>Dead Global Elimination</td></tr>
<tr><td><a href="#globalopt">-globalopt</a></td><td>Global Variable Optimizer</td></tr>
<tr><td><a href="#gvn">-gvn</a></td><td>Global Value Numbering</td></tr>
-<tr><td><a href="#gvnpre">-gvnpre</a></td><td>Global Value Numbering/Partial Redundancy Elimination</td></tr>
-<tr><td><a href="#indmemrem">-indmemrem</a></td><td>Indirect Malloc and Free Removal</td></tr>
<tr><td><a href="#indvars">-indvars</a></td><td>Canonicalize Induction Variables</td></tr>
<tr><td><a href="#inline">-inline</a></td><td>Function Integration/Inlining</td></tr>
-<tr><td><a href="#insert-block-profiling">-insert-block-profiling</a></td><td>Insert instrumentation for block profiling</td></tr>
<tr><td><a href="#insert-edge-profiling">-insert-edge-profiling</a></td><td>Insert instrumentation for edge profiling</td></tr>
-<tr><td><a href="#insert-function-profiling">-insert-function-profiling</a></td><td>Insert instrumentation for function profiling</td></tr>
-<tr><td><a href="#insert-null-profiling-rs">-insert-null-profiling-rs</a></td><td>Measure profiling framework overhead</td></tr>
-<tr><td><a href="#insert-rs-profiling-framework">-insert-rs-profiling-framework</a></td><td>Insert random sampling instrumentation framework</td></tr>
+<tr><td><a href="#insert-optimal-edge-profiling">-insert-optimal-edge-profiling</a></td><td>Insert optimal instrumentation for edge profiling</td></tr>
<tr><td><a href="#instcombine">-instcombine</a></td><td>Combine redundant instructions</td></tr>
<tr><td><a href="#internalize">-internalize</a></td><td>Internalize Global Symbols</td></tr>
<tr><td><a href="#ipconstprop">-ipconstprop</a></td><td>Interprocedural constant propagation</td></tr>
<tr><td><a href="#ipsccp">-ipsccp</a></td><td>Interprocedural Sparse Conditional Constant Propagation</td></tr>
+<tr><td><a href="#jump-threading">-jump-threading</a></td><td>Jump Threading</td></tr>
<tr><td><a href="#lcssa">-lcssa</a></td><td>Loop-Closed SSA Form Pass</td></tr>
<tr><td><a href="#licm">-licm</a></td><td>Loop Invariant Code Motion</td></tr>
+<tr><td><a href="#loop-deletion">-loop-deletion</a></td><td>Delete dead loops</td></tr>
<tr><td><a href="#loop-extract">-loop-extract</a></td><td>Extract loops into new functions</td></tr>
<tr><td><a href="#loop-extract-single">-loop-extract-single</a></td><td>Extract at most one loop into a new function</td></tr>
-<tr><td><a href="#loop-index-split">-loop-index-split</a></td><td>Index Split Loops</td></tr>
<tr><td><a href="#loop-reduce">-loop-reduce</a></td><td>Loop Strength Reduction</td></tr>
<tr><td><a href="#loop-rotate">-loop-rotate</a></td><td>Rotate Loops</td></tr>
+<tr><td><a href="#loop-simplify">-loop-simplify</a></td><td>Canonicalize natural loops</td></tr>
<tr><td><a href="#loop-unroll">-loop-unroll</a></td><td>Unroll loops</td></tr>
<tr><td><a href="#loop-unswitch">-loop-unswitch</a></td><td>Unswitch loops</td></tr>
-<tr><td><a href="#loopsimplify">-loopsimplify</a></td><td>Canonicalize natural loops</td></tr>
-<tr><td><a href="#lower-packed">-lower-packed</a></td><td>lowers packed operations to operations on smaller packed datatypes</td></tr>
-<tr><td><a href="#lowerallocs">-lowerallocs</a></td><td>Lower allocations from instructions to calls</td></tr>
-<tr><td><a href="#lowergc">-lowergc</a></td><td>Lower GC intrinsics, for GCless code generators</td></tr>
+<tr><td><a href="#loweratomic">-loweratomic</a></td><td>Lower atomic intrinsics to non-atomic form</td></tr>
<tr><td><a href="#lowerinvoke">-lowerinvoke</a></td><td>Lower invoke and unwind, for unwindless code generators</td></tr>
-<tr><td><a href="#lowerselect">-lowerselect</a></td><td>Lower select instructions to branches</td></tr>
-<tr><td><a href="#lowersetjmp">-lowersetjmp</a></td><td>Lower Set Jump</td></tr>
<tr><td><a href="#lowerswitch">-lowerswitch</a></td><td>Lower SwitchInst's to branches</td></tr>
<tr><td><a href="#mem2reg">-mem2reg</a></td><td>Promote Memory to Register</td></tr>
+<tr><td><a href="#memcpyopt">-memcpyopt</a></td><td>MemCpy Optimization</td></tr>
+<tr><td><a href="#mergefunc">-mergefunc</a></td><td>Merge Functions</td></tr>
<tr><td><a href="#mergereturn">-mergereturn</a></td><td>Unify function exit nodes</td></tr>
-<tr><td><a href="#predsimplify">-predsimplify</a></td><td>Predicate Simplifier</td></tr>
+<tr><td><a href="#partial-inliner">-partial-inliner</a></td><td>Partial Inliner</td></tr>
<tr><td><a href="#prune-eh">-prune-eh</a></td><td>Remove unused exception handling info</td></tr>
-<tr><td><a href="#raiseallocs">-raiseallocs</a></td><td>Raise allocations from calls to instructions</td></tr>
<tr><td><a href="#reassociate">-reassociate</a></td><td>Reassociate expressions</td></tr>
<tr><td><a href="#reg2mem">-reg2mem</a></td><td>Demote all values to stack slots</td></tr>
-<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates</td></tr>
+<tr><td><a href="#scalarrepl">-scalarrepl</a></td><td>Scalar Replacement of Aggregates (DT)</td></tr>
<tr><td><a href="#sccp">-sccp</a></td><td>Sparse Conditional Constant Propagation</td></tr>
<tr><td><a href="#simplify-libcalls">-simplify-libcalls</a></td><td>Simplify well-known library calls</td></tr>
<tr><td><a href="#simplifycfg">-simplifycfg</a></td><td>Simplify the CFG</td></tr>
+<tr><td><a href="#sink">-sink</a></td><td>Code sinking</td></tr>
+<tr><td><a href="#sretpromotion">-sretpromotion</a></td><td>Promote sret arguments to multiple ret values</td></tr>
<tr><td><a href="#strip">-strip</a></td><td>Strip all symbols from a module</td></tr>
+<tr><td><a href="#strip-dead-debug-info">-strip-dead-debug-info</a></td><td>Strip debug info for unused symbols</td></tr>
+<tr><td><a href="#strip-dead-prototypes">-strip-dead-prototypes</a></td><td>Strip Unused Function Prototypes</td></tr>
+<tr><td><a href="#strip-debug-declare">-strip-debug-declare</a></td><td>Strip all llvm.dbg.declare intrinsics</td></tr>
+<tr><td><a href="#strip-nondebug">-strip-nondebug</a></td><td>Strip all symbols, except dbg symbols, from a module</td></tr>
<tr><td><a href="#tailcallelim">-tailcallelim</a></td><td>Tail Call Elimination</td></tr>
<tr><td><a href="#tailduplicate">-tailduplicate</a></td><td>Tail Duplication</td></tr>
<tr><th>Option</th><th>Name</th></tr>
<tr><td><a href="#deadarghaX0r">-deadarghaX0r</a></td><td>Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</td></tr>
<tr><td><a href="#extract-blocks">-extract-blocks</a></td><td>Extract Basic Blocks From Module (for bugpoint use)</td></tr>
-<tr><td><a href="#emitbitcode">-emitbitcode</a></td><td>Bitcode Writer</td></tr>
+<tr><td><a href="#instnamer">-instnamer</a></td><td>Assign names to anonymous instructions</td></tr>
+<tr><td><a href="#preverify">-preverify</a></td><td>Preliminary module verification</td></tr>
<tr><td><a href="#verify">-verify</a></td><td>Module Verifier</td></tr>
<tr><td><a href="#view-cfg">-view-cfg</a></td><td>View CFG of function</td></tr>
<tr><td><a href="#view-cfg-only">-view-cfg-only</a></td><td>View CFG of function (with no function bodies)</td></tr>
+<tr><td><a href="#view-dom">-view-dom</a></td><td>View dominance tree of function</td></tr>
+<tr><td><a href="#view-dom-only">-view-dom-only</a></td><td>View dominance tree of function (with no function bodies)</td></tr>
+<tr><td><a href="#view-postdom">-view-postdom</a></td><td>View postdominance tree of function</td></tr>
+<tr><td><a href="#view-postdom-only">-view-postdom-only</a></td><td>View postdominance tree of function (with no function bodies)</td></tr>
</table>
+
</div>
<!-- ======================================================================= -->
-<div class="doc_section"> <a name="example">Analysis Passes</a></div>
-<div class="doc_text">
+<h2><a name="analyses">Analysis Passes</a></h2>
+<div>
<p>This section describes the LLVM Analysis Passes.</p>
-</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="aa-eval">Exhaustive Alias Analysis Precision Evaluator</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="aa-eval">-aa-eval: Exhaustive Alias Analysis Precision Evaluator</a>
+</h3>
+<div>
<p>This is a simple N^2 alias analysis accuracy evaluator.
Basically, for each function in the program, it simply queries to see how the
alias analysis implementation answers alias queries between each pair of
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="anders-aa">Andersen's Interprocedural Alias Analysis</a>
-</div>
-<div class="doc_text">
- <p>
- This is an implementation of Andersen's interprocedural alias
- analysis
- </p>
-
- <p>
- In pointer analysis terms, this is a subset-based, flow-insensitive,
- field-sensitive, and context-insensitive algorithm pointer algorithm.
- </p>
-
- <p>
- This algorithm is implemented as three stages:
- </p>
-
- <ol>
- <li>Object identification.</li>
- <li>Inclusion constraint identification.</li>
- <li>Offline constraint graph optimization.</li>
- <li>Inclusion constraint solving.</li>
- </ol>
-
- <p>
- The object identification stage identifies all of the memory objects in the
- program, which includes globals, heap allocated objects, and stack allocated
- objects.
- </p>
-
- <p>
- The inclusion constraint identification stage finds all inclusion constraints
- in the program by scanning the program, looking for pointer assignments and
- other statements that effect the points-to graph. For a statement like
- <code><var>A</var> = <var>B</var></code>, this statement is processed to
- indicate that <var>A</var> can point to anything that <var>B</var> can point
- to. Constraints can handle copies, loads, and stores, and address taking.
- </p>
-
- <p>
- The offline constraint graph optimization portion includes offline variable
- substitution algorithms intended to computer pointer and location
- equivalences. Pointer equivalences are those pointers that will have the
- same points-to sets, and location equivalences are those variables that
- always appear together in points-to sets.
- </p>
-
- <p>
- The inclusion constraint solving phase iteratively propagates the inclusion
- constraints until a fixed point is reached. This is an O(<var>n</var>³)
- algorithm.
- </p>
-
- <p>
- Function constraints are handled as if they were structs with <var>X</var>
- fields. Thus, an access to argument <var>X</var> of function <var>Y</var> is
- an access to node index <code>getNode(<var>Y</var>) + <var>X</var></code>.
- This representation allows handling of indirect calls without any issues. To
- wit, an indirect call <code><var>Y</var>(<var>a</var>,<var>b</var>)</code> is
- equivalent to <code>*(<var>Y</var> + 1) = <var>a</var>, *(<var>Y</var> + 2) =
- <var>b</var></code>. The return node for a function <var>F</var> is always
- located at <code>getNode(<var>F</var>) + CallReturnPos</code>. The arguments
- start at <code>getNode(<var>F</var>) + CallArgPos</code>.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="basicaa">Basic Alias Analysis (default AA impl)</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="basicaa">-basicaa: Basic Alias Analysis (stateless AA impl)</a>
+</h3>
+<div>
<p>
This is the default implementation of the Alias Analysis interface
that simply implements a few identities (two different globals cannot alias,
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="basiccg">Basic CallGraph Construction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="basiccg">-basiccg: Basic CallGraph Construction</a>
+</h3>
+<div>
<p>Yet to be written.</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="basicvn">Basic Value Numbering (default GVN impl)</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="count-aa">-count-aa: Count Alias Analysis Query Responses</a>
+</h3>
+<div>
<p>
- This is the default implementation of the <code>ValueNumbering</code>
- interface. It walks the SSA def-use chains to trivially identify
- lexically identical expressions. This does not require any ahead of time
- analysis, so it is a very fast default implementation.
+ A pass which can be used to count how many alias queries
+ are being made and how the alias analysis implementation being used responds.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="callgraph">Print a call graph</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="debug-aa">-debug-aa: AA use debugger</a>
+</h3>
+<div>
<p>
- This pass, only available in <code>opt</code>, prints the call graph to
- standard output in a human-readable form.
+ This simple pass checks alias analysis users to ensure that if they
+ create a new value, they do not query AA without informing it of the value.
+ It acts as a shim over any other AA pass you want.
+ </p>
+
+ <p>
+ Yes keeping track of every value in the program is expensive, but this is
+ a debugging pass.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="callscc">Print SCCs of the Call Graph</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="domfrontier">-domfrontier: Dominance Frontier Construction</a>
+</h3>
+<div>
<p>
- This pass, only available in <code>opt</code>, prints the SCCs of the call
- graph to standard output in a human-readable form.
+ This pass is a simple dominator construction algorithm for finding forward
+ dominator frontiers.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="cfgscc">Print SCCs of each function CFG</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="domtree">-domtree: Dominator Tree Construction</a>
+</h3>
+<div>
<p>
- This pass, only available in <code>opt</code>, prints the SCCs of each
- function CFG to standard output in a human-readable form.
+ This pass is a simple dominator construction algorithm for finding forward
+ dominators.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="codegenprepare">Optimize for code generation</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dot-callgraph">-dot-callgraph: Print Call Graph to 'dot' file</a>
+</h3>
+<div>
<p>
- This pass munges the code in the input function to better prepare it for
- SelectionDAG-based code generation. This works around limitations in it's
- basic-block-at-a-time approach. It should eventually be removed.
+ This pass, only available in <code>opt</code>, prints the call graph into a
+ <code>.dot</code> graph. This graph can then be processed with the "dot" tool
+ to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="count-aa">Count Alias Analysis Query Responses</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dot-cfg">-dot-cfg: Print CFG of function to 'dot' file</a>
+</h3>
+<div>
<p>
- A pass which can be used to count how many alias queries
- are being made and how the alias analysis implementation being used responds.
+ This pass, only available in <code>opt</code>, prints the control flow graph
+ into a <code>.dot</code> graph. This graph can then be processed with the
+ "dot" tool to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="debug-aa">AA use debugger</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dot-cfg-only">-dot-cfg-only: Print CFG of function to 'dot' file (with no function bodies)</a>
+</h3>
+<div>
<p>
- This simple pass checks alias analysis users to ensure that if they
- create a new value, they do not query AA without informing it of the value.
- It acts as a shim over any other AA pass you want.
+ This pass, only available in <code>opt</code>, prints the control flow graph
+ into a <code>.dot</code> graph, omitting the function bodies. This graph can
+ then be processed with the "dot" tool to convert it to postscript or some
+ other suitable format.
</p>
-
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="dot-dom">-dot-dom: Print dominance tree of function to 'dot' file</a>
+</h3>
+<div>
<p>
- Yes keeping track of every value in the program is expensive, but this is
- a debugging pass.
+ This pass, only available in <code>opt</code>, prints the dominator tree
+ into a <code>.dot</code> graph. This graph can then be processed with the
+ "dot" tool to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="domfrontier">Dominance Frontier Construction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dot-dom-only">-dot-dom-only: Print dominance tree of function to 'dot' file (with no function bodies)</a>
+</h3>
+<div>
<p>
- This pass is a simple dominator construction algorithm for finding forward
- dominator frontiers.
+ This pass, only available in <code>opt</code>, prints the dominator tree
+ into a <code>.dot</code> graph, omitting the function bodies. This graph can
+ then be processed with the "dot" tool to convert it to postscript or some
+ other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="domtree">Dominator Tree Construction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dot-postdom">-dot-postdom: Print postdominance tree of function to 'dot' file</a>
+</h3>
+<div>
<p>
- This pass is a simple dominator construction algorithm for finding forward
- dominators.
+ This pass, only available in <code>opt</code>, prints the post dominator tree
+ into a <code>.dot</code> graph. This graph can then be processed with the
+ "dot" tool to convert it to postscript or some other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="externalfnconstants">Print external fn callsites passed constants</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dot-postdom-only">-dot-postdom-only: Print postdominance tree of function to 'dot' file (with no function bodies)</a>
+</h3>
+<div>
<p>
- This pass, only available in <code>opt</code>, prints out call sites to
- external functions that are called with constant arguments. This can be
- useful when looking for standard library functions we should constant fold
- or handle in alias analyses.
+ This pass, only available in <code>opt</code>, prints the post dominator tree
+ into a <code>.dot</code> graph, omitting the function bodies. This graph can
+ then be processed with the "dot" tool to convert it to postscript or some
+ other suitable format.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="globalsmodref-aa">Simple mod/ref analysis for globals</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="globalsmodref-aa">-globalsmodref-aa: Simple mod/ref analysis for globals</a>
+</h3>
+<div>
<p>
This simple pass provides alias and mod/ref information for global values
that do not have their address taken, and keeps track of whether functions
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="instcount">Counts the various types of Instructions</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="instcount">-instcount: Counts the various types of Instructions</a>
+</h3>
+<div>
<p>
This pass collects the count of all instructions and reports them
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="intervals">Interval Partition Construction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="intervals">-intervals: Interval Partition Construction</a>
+</h3>
+<div>
<p>
This analysis calculates and represents the interval partition of a function,
or a preexisting interval partition.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="load-vn">Load Value Numbering</a>
+<h3>
+ <a name="iv-users">-iv-users: Induction Variable Users</a>
+</h3>
+<div>
+ <p>Bookkeeping for "interesting" users of expressions computed from
+ induction variables.</p>
</div>
-<div class="doc_text">
- <p>
- This pass value numbers load and call instructions. To do this, it finds
- lexically identical load instructions, and uses alias analysis to determine
- which loads are guaranteed to produce the same value. To value number call
- instructions, it looks for calls to functions that do not write to memory
- which do not have intervening instructions that clobber the memory that is
- read from.
- </p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lazy-value-info">-lazy-value-info: Lazy Value Information Analysis</a>
+</h3>
+<div>
+ <p>Interface for lazy computation of value constraint information.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lda">-lda: Loop Dependence Analysis</a>
+</h3>
+<div>
+ <p>Loop dependence analysis framework, which is used to detect dependences in
+ memory accesses in loops.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="libcall-aa">-libcall-aa: LibCall Alias Analysis</a>
+</h3>
+<div>
+ <p>LibCall Alias Analysis.</p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lint">-lint: Statically lint-checks LLVM IR</a>
+</h3>
+<div>
+ <p>This pass statically checks for common and easily-identified constructs
+ which produce undefined or likely unintended behavior in LLVM IR.</p>
+
+ <p>It is not a guarantee of correctness, in two ways. First, it isn't
+ comprehensive. There are checks which could be done statically which are
+ not yet implemented. Some of these are indicated by TODO comments, but
+ those aren't comprehensive either. Second, many conditions cannot be
+ checked statically. This pass does no dynamic instrumentation, so it
+ can't check for all possible problems.</p>
- <p>
- This pass builds off of another value numbering pass to implement value
- numbering for non-load and non-call instructions. It uses Alias Analysis so
- that it can disambiguate the load instructions. The more powerful these base
- analyses are, the more powerful the resultant value numbering will be.
+ <p>Another limitation is that it assumes all code will be executed. A store
+ through a null pointer in a basic block which is never reached is harmless,
+ but this pass will warn about it anyway.</p>
+
+ <p>Optimization passes may make conditions that this pass checks for more or
+ less obvious. If an optimization pass appears to be introducing a warning,
+ it may be that the optimization pass is merely exposing an existing
+ condition in the code.</p>
+
+ <p>This code may be run before instcombine. In many cases, instcombine checks
+ for the same kinds of things and turns instructions with undefined behavior
+ into unreachable (or equivalent). Because of this, this pass makes some
+ effort to look through bitcasts and so on.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loops">Natural Loop Construction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loops">-loops: Natural Loop Information</a>
+</h3>
+<div>
<p>
This analysis is used to identify natural loops and determine the loop depth
of various nodes of the CFG. Note that the loops identified may actually be
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="memdep">Memory Dependence Analysis</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="memdep">-memdep: Memory Dependence Analysis</a>
+</h3>
+<div>
<p>
An analysis that determines, for a given memory operation, what preceding
memory operations it depends on. It builds on alias analysis information, and
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="no-aa">No Alias Analysis (always returns 'may' alias)</a>
+<h3>
+ <a name="module-debuginfo">-module-debuginfo: Decodes module-level debug info</a>
+</h3>
+<div>
+ <p>This pass decodes the debug info metadata in a module and prints in a
+ (sufficiently-prepared-) human-readable form.
+
+ For example, run this pass from opt along with the -analyze option, and
+ it'll print to standard output.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="no-aa">-no-aa: No Alias Analysis (always returns 'may' alias)</a>
+</h3>
+<div>
<p>
Always returns "I don't know" for alias queries. NoAA is unlike other alias
analysis implementations, in that it does not chain to a previous analysis. As
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="no-profile">No Profile Information</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="no-profile">-no-profile: No Profile Information</a>
+</h3>
+<div>
<p>
The default "no profile" implementation of the abstract
<code>ProfileInfo</code> interface.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="postdomfrontier">Post-Dominance Frontier Construction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="postdomfrontier">-postdomfrontier: Post-Dominance Frontier Construction</a>
+</h3>
+<div>
<p>
This pass is a simple post-dominator construction algorithm for finding
post-dominator frontiers.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="postdomtree">Post-Dominator Tree Construction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="postdomtree">-postdomtree: Post-Dominator Tree Construction</a>
+</h3>
+<div>
<p>
This pass is a simple post-dominator construction algorithm for finding
post-dominators.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="print">Print function to stderr</a>
+<h3>
+ <a name="print-alias-sets">-print-alias-sets: Alias Set Printer</a>
+</h3>
+<div>
+ <p>Yet to be written.</p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-callgraph">-print-callgraph: Print a call graph</a>
+</h3>
+<div>
<p>
- The <code>PrintFunctionPass</code> class is designed to be pipelined with
- other <code>FunctionPass</code>es, and prints out the functions of the module
- as they are processed.
+ This pass, only available in <code>opt</code>, prints the call graph to
+ standard error in a human-readable form.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="print-alias-sets">Alias Set Printer</a>
-</div>
-<div class="doc_text">
- <p>Yet to be written.</p>
+<h3>
+ <a name="print-callgraph-sccs">-print-callgraph-sccs: Print SCCs of the Call Graph</a>
+</h3>
+<div>
+ <p>
+ This pass, only available in <code>opt</code>, prints the SCCs of the call
+ graph to standard error in a human-readable form.
+ </p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="print-callgraph">Print Call Graph to 'dot' file</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="print-cfg-sccs">-print-cfg-sccs: Print SCCs of each function CFG</a>
+</h3>
+<div>
<p>
- This pass, only available in <code>opt</code>, prints the call graph into a
- <code>.dot</code> graph. This graph can then be processed with the "dot" tool
- to convert it to postscript or some other suitable format.
+ This pass, only available in <code>opt</code>, prints the SCCs of each
+ function CFG to standard error in a human-readable form.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="print-cfg">Print CFG of function to 'dot' file</a>
+<h3>
+ <a name="print-dbginfo">-print-dbginfo: Print debug info in human readable form</a>
+</h3>
+<div>
+ <p>Pass that prints instructions, and associated debug info:</p>
+ <ul>
+
+ <li>source/line/col information</li>
+ <li>original variable name</li>
+ <li>original type name</li>
+ </ul>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-dom-info">-print-dom-info: Dominator Info Printer</a>
+</h3>
+<div>
+ <p>Dominator Info Printer.</p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="print-externalfnconstants">-print-externalfnconstants: Print external fn callsites passed constants</a>
+</h3>
+<div>
<p>
- This pass, only available in <code>opt</code>, prints the control flow graph
- into a <code>.dot</code> graph. This graph can then be processed with the
- "dot" tool to convert it to postscript or some other suitable format.
+ This pass, only available in <code>opt</code>, prints out call sites to
+ external functions that are called with constant arguments. This can be
+ useful when looking for standard library functions we should constant fold
+ or handle in alias analyses.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="print-cfg-only">Print CFG of function to 'dot' file (with no function bodies)</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="print-function">-print-function: Print function to stderr</a>
+</h3>
+<div>
<p>
- This pass, only available in <code>opt</code>, prints the control flow graph
- into a <code>.dot</code> graph, omitting the function bodies. This graph can
- then be processed with the "dot" tool to convert it to postscript or some
- other suitable format.
+ The <code>PrintFunctionPass</code> class is designed to be pipelined with
+ other <code>FunctionPass</code>es, and prints out the functions of the module
+ as they are processed.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="printm">Print module to stderr</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="print-module">-print-module: Print module to stderr</a>
+</h3>
+<div>
<p>
This pass simply prints out the entire module when it is executed.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="printusedtypes">Find Used Types</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="print-used-types">-print-used-types: Find Used Types</a>
+</h3>
+<div>
<p>
This pass is used to seek out all of the types in use by the program. Note
that this analysis explicitly does not include types only used by the symbol
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="profile-loader">Load profile information from llvmprof.out</a>
+<h3>
+ <a name="profile-estimator">-profile-estimator: Estimate profiling information</a>
+</h3>
+<div>
+ <p>Profiling information that estimates the profiling information
+ in a very crude and unimaginative way.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="profile-loader">-profile-loader: Load profile information from llvmprof.out</a>
+</h3>
+<div>
<p>
A concrete implementation of profiling information that loads the information
from a profile dump file.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="scalar-evolution">Scalar Evolution Analysis</a>
+<h3>
+ <a name="profile-verifier">-profile-verifier: Verify profiling information</a>
+</h3>
+<div>
+ <p>Pass that checks profiling information for plausibility.</p>
+</div>
+<h3>
+ <a name="regions">-regions: Detect single entry single exit regions</a>
+</h3>
+<div>
+ <p>
+ The <code>RegionInfo</code> pass detects single entry single exit regions in a
+ function, where a region is defined as any subgraph that is connected to the
+ remaining graph at only two spots. Furthermore, an hierarchical region tree is
+ built.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="scalar-evolution">-scalar-evolution: Scalar Evolution Analysis</a>
+</h3>
+<div>
<p>
The <code>ScalarEvolution</code> analysis can be used to analyze and
catagorize scalar expressions in loops. It specializes in recognizing general
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="targetdata">Target Data Layout</a>
+<h3>
+ <a name="scev-aa">-scev-aa: ScalarEvolution-based Alias Analysis</a>
+</h3>
+<div>
+ <p>Simple alias analysis implemented in terms of ScalarEvolution queries.
+
+ This differs from traditional loop dependence analysis in that it tests
+ for dependencies within a single iteration of a loop, rather than
+ dependencies between different iterations.
+
+ ScalarEvolution has a more complete understanding of pointer arithmetic
+ than BasicAliasAnalysis' collection of ad-hoc analyses.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="targetdata">-targetdata: Target Data Layout</a>
+</h3>
+<div>
<p>Provides other passes access to information on how the size and alignment
required by the the target ABI for various data types.</p>
</div>
+</div>
+
<!-- ======================================================================= -->
-<div class="doc_section"> <a name="transform">Transform Passes</a></div>
-<div class="doc_text">
+<h2><a name="transforms">Transform Passes</a></h2>
+<div>
<p>This section describes the LLVM Transform Passes.</p>
-</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="adce">Aggressive Dead Code Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="adce">-adce: Aggressive Dead Code Elimination</a>
+</h3>
+<div>
<p>ADCE aggressively tries to eliminate code. This pass is similar to
<a href="#dce">DCE</a> but it assumes that values are dead until proven
otherwise. This is similar to <a href="#sccp">SCCP</a>, except applied to
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="argpromotion">Promote 'by reference' arguments to scalars</a>
+<h3>
+ <a name="always-inline">-always-inline: Inliner for always_inline functions</a>
+</h3>
+<div>
+ <p>A custom inliner that handles only functions that are marked as
+ "always inline".</p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="argpromotion">-argpromotion: Promote 'by reference' arguments to scalars</a>
+</h3>
+<div>
<p>
This pass promotes "by reference" arguments to be "by value" arguments. In
practice, this means looking for internal functions that have pointer
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="block-placement">Profile Guided Basic Block Placement</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="block-placement">-block-placement: Profile Guided Basic Block Placement</a>
+</h3>
+<div>
<p>This pass is a very simple profile guided basic block placement algorithm.
The idea is to put frequently executed blocks together at the start of the
function and hopefully increase the number of fall-through conditional
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="break-crit-edges">Break critical edges in CFG</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="break-crit-edges">-break-crit-edges: Break critical edges in CFG</a>
+</h3>
+<div>
<p>
Break all of the critical edges in the CFG by inserting a dummy basic block.
It may be "required" by passes that cannot deal with critical edges. This
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="cee">Correlated Expression Elimination</a>
-</div>
-<div class="doc_text">
- <p>Correlated Expression Elimination propagates information from conditional
- branches to blocks dominated by destinations of the branch. It propagates
- information from the condition check itself into the body of the branch,
- allowing transformations like these for example:</p>
-
-<blockquote><pre>
-if (i == 7)
- ... 4*i; // constant propagation
-
-M = i+1; N = j+1;
-if (i == j)
- X = M-N; // = M-M == 0;
-</pre></blockquote>
-
- <p>This is called Correlated Expression Elimination because we eliminate or
- simplify expressions that are correlated with the direction of a branch. In
- this way we use static information to give us some information about the
- dynamic value of a variable.</p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="condprop">Conditional Propagation</a>
-</div>
-<div class="doc_text">
- <p>This pass propagates information about conditional expressions through the
- program, allowing it to eliminate conditional branches in some cases.</p>
+<h3>
+ <a name="codegenprepare">-codegenprepare: Optimize for code generation</a>
+</h3>
+<div>
+ This pass munges the code in the input function to better prepare it for
+ SelectionDAG-based code generation. This works around limitations in it's
+ basic-block-at-a-time approach. It should eventually be removed.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="constmerge">Merge Duplicate Global Constants</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="constmerge">-constmerge: Merge Duplicate Global Constants</a>
+</h3>
+<div>
<p>
Merges duplicate global constants together into a single constant that is
shared. This is useful because some passes (ie TraceValues) insert a lot of
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="constprop">Simple constant propagation</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="constprop">-constprop: Simple constant propagation</a>
+</h3>
+<div>
<p>This file implements constant propagation and merging. It looks for
instructions involving only constant operands and replaces them with a
constant value instead of an instruction. For example:</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="dce">Dead Code Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dce">-dce: Dead Code Elimination</a>
+</h3>
+<div>
<p>
Dead code elimination is similar to <a href="#die">dead instruction
elimination</a>, but it rechecks instructions that were used by removed
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="deadargelim">Dead Argument Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="deadargelim">-deadargelim: Dead Argument Elimination</a>
+</h3>
+<div>
<p>
This pass deletes dead arguments from internal functions. Dead argument
elimination removes arguments which are directly dead, as well as arguments
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="deadtypeelim">Dead Type Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="deadtypeelim">-deadtypeelim: Dead Type Elimination</a>
+</h3>
+<div>
<p>
This pass is used to cleanup the output of GCC. It eliminate names for types
that are unused in the entire translation unit, using the <a
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="die">Dead Instruction Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="die">-die: Dead Instruction Elimination</a>
+</h3>
+<div>
<p>
Dead instruction elimination performs a single pass over the function,
removing instructions that are obviously dead.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="dse">Dead Store Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="dse">-dse: Dead Store Elimination</a>
+</h3>
+<div>
<p>
A trivial dead store elimination that only considers basic-block local
redundant stores.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="gcse">Global Common Subexpression Elimination</a>
-</div>
-<div class="doc_text">
- <p>
- This pass is designed to be a very quick global transformation that
- eliminates global common subexpressions from a function. It does this by
- using an existing value numbering implementation to identify the common
- subexpressions, eliminating them when possible.
+<h3>
+ <a name="functionattrs">-functionattrs: Deduce function attributes</a>
+</h3>
+<div>
+ <p>A simple interprocedural pass which walks the call-graph, looking for
+ functions which do not access or only read non-local memory, and marking them
+ readnone/readonly. In addition, it marks function arguments (of pointer type)
+ 'nocapture' if a call to the function does not create any copies of the pointer
+ value that outlive the call. This more or less means that the pointer is only
+ dereferenced, and not returned from the function or stored in a global.
+ This pass is implemented as a bottom-up traversal of the call-graph.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="globaldce">Dead Global Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="globaldce">-globaldce: Dead Global Elimination</a>
+</h3>
+<div>
<p>
This transform is designed to eliminate unreachable internal globals from the
program. It uses an aggressive algorithm, searching out globals that are
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="globalopt">Global Variable Optimizer</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="globalopt">-globalopt: Global Variable Optimizer</a>
+</h3>
+<div>
<p>
This pass transforms simple global variables that never have their address
taken. If obviously true, it marks read/write globals as constant, deletes
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="gvn">Global Value Numbering</a>
-</div>
-<div class="doc_text">
- <p>
- This pass performs global value numbering to eliminate fully redundant
- instructions. It also performs simple dead load elimination.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="gvnpre">Global Value Numbering/Partial Redundancy Elimination</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="gvn">-gvn: Global Value Numbering</a>
+</h3>
+<div>
<p>
- This pass performs a hybrid of global value numbering and partial redundancy
- elimination, known as GVN-PRE. It performs partial redundancy elimination on
- values, rather than lexical expressions, allowing a more comprehensive view
- the optimization. It replaces redundant values with uses of earlier
- occurences of the same value. While this is beneficial in that it eliminates
- unneeded computation, it also increases register pressure by creating large
- live ranges, and should be used with caution on platforms that are very
- sensitive to register pressure.
+ This pass performs global value numbering to eliminate fully and partially
+ redundant instructions. It also performs redundant load elimination.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="indmemrem">Indirect Malloc and Free Removal</a>
-</div>
-<div class="doc_text">
- <p>
- This pass finds places where memory allocation functions may escape into
- indirect land. Some transforms are much easier (aka possible) only if free
- or malloc are not called indirectly.
- </p>
-
- <p>
- Thus find places where the address of memory functions are taken and construct
- bounce functions with direct calls of those functions.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="indvars">Canonicalize Induction Variables</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="indvars">-indvars: Canonicalize Induction Variables</a>
+</h3>
+<div>
<p>
This transformation analyzes and transforms the induction variables (and
computations derived from them) into simpler forms suitable for subsequent
the dependence on the exit value of the induction variable. If the only
purpose of the loop is to compute the exit value of some derived
expression, this transformation will make the loop dead.</li>
- </p>
+ </ol>
<p>
This transformation should be followed by strength reduction after all of the
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="inline">Function Integration/Inlining</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="inline">-inline: Function Integration/Inlining</a>
+</h3>
+<div>
<p>
Bottom-up inlining of functions into callees.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="insert-block-profiling">Insert instrumentation for block profiling</a>
-</div>
-<div class="doc_text">
- <p>
- This pass instruments the specified program with counters for basic block
- profiling, which counts the number of times each basic block executes. This
- is the most basic form of profiling, which can tell which blocks are hot, but
- cannot reliably detect hot paths through the CFG.
- </p>
-
- <p>
- Note that this implementation is very naïve. Control equivalent regions of
- the CFG should not require duplicate counters, but it does put duplicate
- counters in.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="insert-edge-profiling">Insert instrumentation for edge profiling</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="insert-edge-profiling">-insert-edge-profiling: Insert instrumentation for edge profiling</a>
+</h3>
+<div>
<p>
This pass instruments the specified program with counters for edge profiling.
Edge profiling can give a reasonable approximation of the hot paths through a
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="insert-function-profiling">Insert instrumentation for function profiling</a>
-</div>
-<div class="doc_text">
- <p>
- This pass instruments the specified program with counters for function
- profiling, which counts the number of times each function is called.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="insert-null-profiling-rs">Measure profiling framework overhead</a>
-</div>
-<div class="doc_text">
- <p>
- The basic profiler that does nothing. It is the default profiler and thus
- terminates <code>RSProfiler</code> chains. It is useful for measuring
- framework overhead.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="insert-rs-profiling-framework">Insert random sampling instrumentation framework</a>
-</div>
-<div class="doc_text">
- <p>
- The second stage of the random-sampling instrumentation framework, duplicates
- all instructions in a function, ignoring the profiling code, then connects the
- two versions together at the entry and at backedges. At each connection point
- a choice is made as to whether to jump to the profiled code (take a sample) or
- execute the unprofiled code.
- </p>
-
- <p>
- After this pass, it is highly recommended to run<a href="#mem2reg">mem2reg</a>
- and <a href="#adce">adce</a>. <a href="#instcombine">instcombine</a>,
- <a href="#load-vn">load-vn</a>, <a href="#gdce">gdce</a>, and
- <a href="#dse">dse</a> also are good to run afterwards.
+<h3>
+ <a name="insert-optimal-edge-profiling">-insert-optimal-edge-profiling: Insert optimal instrumentation for edge profiling</a>
+</h3>
+<div>
+ <p>This pass instruments the specified program with counters for edge profiling.
+ Edge profiling can give a reasonable approximation of the hot paths through a
+ program, and is used for a wide variety of program transformations.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="instcombine">Combine redundant instructions</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="instcombine">-instcombine: Combine redundant instructions</a>
+</h3>
+<div>
<p>
Combine instructions to form fewer, simple
instructions. This pass does not modify the CFG This pass is where algebraic
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="internalize">Internalize Global Symbols</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="internalize">-internalize: Internalize Global Symbols</a>
+</h3>
+<div>
<p>
This pass loops over all of the functions in the input module, looking for a
main function. If a main function is found, all other functions and all
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="ipconstprop">Interprocedural constant propagation</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="ipconstprop">-ipconstprop: Interprocedural constant propagation</a>
+</h3>
+<div>
<p>
This pass implements an <em>extremely</em> simple interprocedural constant
propagation pass. It could certainly be improved in many different ways,
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="ipsccp">Interprocedural Sparse Conditional Constant Propagation</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="ipsccp">-ipsccp: Interprocedural Sparse Conditional Constant Propagation</a>
+</h3>
+<div>
<p>
An interprocedural variant of <a href="#sccp">Sparse Conditional Constant
Propagation</a>.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lcssa">Loop-Closed SSA Form Pass</a>
+<h3>
+ <a name="jump-threading">-jump-threading: Jump Threading</a>
+</h3>
+<div>
+ <p>
+ Jump threading tries to find distinct threads of control flow running through
+ a basic block. This pass looks at blocks that have multiple predecessors and
+ multiple successors. If one or more of the predecessors of the block can be
+ proven to always cause a jump to one of the successors, we forward the edge
+ from the predecessor to the successor by duplicating the contents of this
+ block.
+ </p>
+ <p>
+ An example of when this can occur is code like this:
+ </p>
+
+ <pre
+>if () { ...
+ X = 4;
+}
+if (X < 3) {</pre>
+
+ <p>
+ In this case, the unconditional branch at the end of the first if can be
+ revectored to the false side of the second if.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="lcssa">-lcssa: Loop-Closed SSA Form Pass</a>
+</h3>
+<div>
<p>
This pass transforms loops by placing phi nodes at the end of the loops for
all values that are live across the loop boundary. For example, it turns
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="licm">Loop Invariant Code Motion</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="licm">-licm: Loop Invariant Code Motion</a>
+</h3>
+<div>
<p>
This pass performs loop invariant code motion, attempting to remove as much
code from the body of a loop as possible. It does this by either hoisting
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loop-extract">Extract loops into new functions</a>
+<h3>
+ <a name="loop-deletion">-loop-deletion: Delete dead loops</a>
+</h3>
+<div>
+ <p>
+ This file implements the Dead Loop Deletion Pass. This pass is responsible
+ for eliminating loops with non-infinite computable trip counts that have no
+ side effects or volatile instructions, and do not contribute to the
+ computation of the function's return value.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="loop-extract">-loop-extract: Extract loops into new functions</a>
+</h3>
+<div>
<p>
A pass wrapper around the <code>ExtractLoop()</code> scalar transformation to
extract each top-level loop into its own new function. If the loop is the
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loop-extract-single">Extract at most one loop into a new function</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loop-extract-single">-loop-extract-single: Extract at most one loop into a new function</a>
+</h3>
+<div>
<p>
Similar to <a href="#loop-extract">Extract loops into new functions</a>,
this pass extracts one natural loop from the program into a function if it
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loop-index-split">Index Split Loops</a>
-</div>
-<div class="doc_text">
- <p>
- This pass divides loop's iteration range by spliting loop such that each
- individual loop is executed efficiently.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loop-reduce">Loop Strength Reduction</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loop-reduce">-loop-reduce: Loop Strength Reduction</a>
+</h3>
+<div>
<p>
This pass performs a strength reduction on array references inside loops that
have as one or more of their components the loop induction variable. This is
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loop-rotate">Rotate Loops</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loop-rotate">-loop-rotate: Rotate Loops</a>
+</h3>
+<div>
<p>A simple loop rotation transformation.</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loop-unroll">Unroll loops</a>
-</div>
-<div class="doc_text">
- <p>
- This pass implements a simple loop unroller. It works best when loops have
- been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
- allowing it to determine the trip counts of loops easily.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loop-unswitch">Unswitch loops</a>
-</div>
-<div class="doc_text">
- <p>
- This pass transforms loops that contain branches on loop-invariant conditions
- to have multiple loops. For example, it turns the left into the right code:
- </p>
-
- <pre
->for (...) if (lic)
- A for (...)
- if (lic) A; B; C
- B else
- C for (...)
- A; C</pre>
-
- <p>
- This can increase the size of the code exponentially (doubling it every time
- a loop is unswitched) so we only unswitch if the resultant code will be
- smaller than a threshold.
- </p>
-
- <p>
- This pass expects LICM to be run before it to hoist invariant conditions out
- of the loop, to make the unswitching opportunity obvious.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="loopsimplify">Canonicalize natural loops</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loop-simplify">-loop-simplify: Canonicalize natural loops</a>
+</h3>
+<div>
<p>
This pass performs several transformations to transform natural loops into a
simpler form, which makes subsequent analyses and transformations simpler and
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lower-packed">lowers packed operations to operations on smaller packed datatypes</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loop-unroll">-loop-unroll: Unroll loops</a>
+</h3>
+<div>
<p>
- Lowers operations on vector datatypes into operations on more primitive vector
- datatypes, and finally to scalar operations.
+ This pass implements a simple loop unroller. It works best when loops have
+ been canonicalized by the <a href="#indvars"><tt>-indvars</tt></a> pass,
+ allowing it to determine the trip counts of loops easily.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lowerallocs">Lower allocations from instructions to calls</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loop-unswitch">-loop-unswitch: Unswitch loops</a>
+</h3>
+<div>
<p>
- Turn <tt>malloc</tt> and <tt>free</tt> instructions into <tt>@malloc</tt> and
- <tt>@free</tt> calls.
+ This pass transforms loops that contain branches on loop-invariant conditions
+ to have multiple loops. For example, it turns the left into the right code:
</p>
-
+
+ <pre
+>for (...) if (lic)
+ A for (...)
+ if (lic) A; B; C
+ B else
+ C for (...)
+ A; C</pre>
+
<p>
- This is a target-dependent tranformation because it depends on the size of
- data types and alignment constraints.
+ This can increase the size of the code exponentially (doubling it every time
+ a loop is unswitched) so we only unswitch if the resultant code will be
+ smaller than a threshold.
+ </p>
+
+ <p>
+ This pass expects LICM to be run before it to hoist invariant conditions out
+ of the loop, to make the unswitching opportunity obvious.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lowergc">Lower GC intrinsics, for GCless code generators</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="loweratomic">-loweratomic: Lower atomic intrinsics to non-atomic form</a>
+</h3>
+<div>
<p>
- This file implements lowering for the <tt>llvm.gc*</tt> intrinsics for targets
- that do not natively support them (which includes the C backend). Note that
- the code generated is not as efficient as it would be for targets that
- natively support the GC intrinsics, but it is useful for getting new targets
- up-and-running quickly.
+ This pass lowers atomic intrinsics to non-atomic form for use in a known
+ non-preemptible environment.
</p>
-
+
<p>
- This pass implements the code transformation described in this paper:
+ The pass does not verify that the environment is non-preemptible (in
+ general this would require knowledge of the entire call graph of the
+ program including any libraries which may not be available in bitcode form);
+ it simply lowers every atomic intrinsic.
</p>
-
- <blockquote><p>
- "Accurate Garbage Collection in an Uncooperative Environment"
- Fergus Henderson, ISMM, 2002
- </p></blockquote>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lowerinvoke">Lower invoke and unwind, for unwindless code generators</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="lowerinvoke">-lowerinvoke: Lower invoke and unwind, for unwindless code generators</a>
+</h3>
+<div>
<p>
This transformation is designed for use by code generators which do not yet
support stack unwinding. This pass supports two models of exception handling
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lowerselect">Lower select instructions to branches</a>
-</div>
-<div class="doc_text">
- <p>
- Lowers select instructions into conditional branches for targets that do not
- have conditional moves or that have not implemented the select instruction
- yet.
- </p>
-
- <p>
- Note that this pass could be improved. In particular it turns every select
- instruction into a new conditional branch, even though some common cases have
- select instructions on the same predicate next to each other. It would be
- better to use the same branch for the whole group of selects.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lowersetjmp">Lower Set Jump</a>
-</div>
-<div class="doc_text">
- <p>
- Lowers <tt>setjmp</tt> and <tt>longjmp</tt> to use the LLVM invoke and unwind
- instructions as necessary.
- </p>
-
- <p>
- Lowering of <tt>longjmp</tt> is fairly trivial. We replace the call with a
- call to the LLVM library function <tt>__llvm_sjljeh_throw_longjmp()</tt>.
- This unwinds the stack for us calling all of the destructors for
- objects allocated on the stack.
- </p>
-
- <p>
- At a <tt>setjmp</tt> call, the basic block is split and the <tt>setjmp</tt>
- removed. The calls in a function that have a <tt>setjmp</tt> are converted to
- invoke where the except part checks to see if it's a <tt>longjmp</tt>
- exception and, if so, if it's handled in the function. If it is, then it gets
- the value returned by the <tt>longjmp</tt> and goes to where the basic block
- was split. <tt>invoke</tt> instructions are handled in a similar fashion with
- the original except block being executed if it isn't a <tt>longjmp</tt>
- except that is handled by that function.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="lowerswitch">Lower SwitchInst's to branches</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="lowerswitch">-lowerswitch: Lower SwitchInst's to branches</a>
+</h3>
+<div>
<p>
Rewrites <tt>switch</tt> instructions with a sequence of branches, which
allows targets to get away with not implementing the switch instruction until
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="mem2reg">Promote Memory to Register</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="mem2reg">-mem2reg: Promote Memory to Register</a>
+</h3>
+<div>
<p>
This file promotes memory references to be register references. It promotes
<tt>alloca</tt> instructions which only have <tt>load</tt>s and
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="mergereturn">Unify function exit nodes</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="memcpyopt">-memcpyopt: MemCpy Optimization</a>
+</h3>
+<div>
<p>
- Ensure that functions have at most one <tt>ret</tt> instruction in them.
- Additionally, it keeps track of which node is the new exit node of the CFG.
+ This pass performs various transformations related to eliminating memcpy
+ calls, or transforming sets of stores into memset's.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="predsimplify">Predicate Simplifier</a>
+<h3>
+ <a name="mergefunc">-mergefunc: Merge Functions</a>
+</h3>
+<div>
+ <p>This pass looks for equivalent functions that are mergable and folds them.
+
+ A hash is computed from the function, based on its type and number of
+ basic blocks.
+
+ Once all hashes are computed, we perform an expensive equality comparison
+ on each function pair. This takes n^2/2 comparisons per bucket, so it's
+ important that the hash function be high quality. The equality comparison
+ iterates through each instruction in each basic block.
+
+ When a match is found the functions are folded. If both functions are
+ overridable, we move the functionality into a new internal function and
+ leave two overridable thunks to it.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="mergereturn">-mergereturn: Unify function exit nodes</a>
+</h3>
+<div>
<p>
- Path-sensitive optimizer. In a branch where <tt>x == y</tt>, replace uses of
- <tt>x</tt> with <tt>y</tt>. Permits further optimization, such as the
- elimination of the unreachable call:
+ Ensure that functions have at most one <tt>ret</tt> instruction in them.
+ Additionally, it keeps track of which node is the new exit node of the CFG.
</p>
-
-<blockquote><pre
->void test(int *p, int *q)
-{
- if (p != q)
- return;
-
- if (*p != *q)
- foo(); // unreachable
-}</pre></blockquote>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="prune-eh">Remove unused exception handling info</a>
+<h3>
+ <a name="partial-inliner">-partial-inliner: Partial Inliner</a>
+</h3>
+<div>
+ <p>This pass performs partial inlining, typically by inlining an if
+ statement that surrounds the body of the function.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="prune-eh">-prune-eh: Remove unused exception handling info</a>
+</h3>
+<div>
<p>
This file implements a simple interprocedural pass which walks the call-graph,
turning <tt>invoke</tt> instructions into <tt>call</tt> instructions if and
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="raiseallocs">Raise allocations from calls to instructions</a>
-</div>
-<div class="doc_text">
- <p>
- Converts <tt>@malloc</tt> and <tt>@free</tt> calls to <tt>malloc</tt> and
- <tt>free</tt> instructions.
- </p>
-</div>
-
-<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="reassociate">Reassociate expressions</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="reassociate">-reassociate: Reassociate expressions</a>
+</h3>
+<div>
<p>
This pass reassociates commutative expressions in an order that is designed
to promote better constant propagation, GCSE, LICM, PRE, etc.
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="reg2mem">Demote all values to stack slots</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="reg2mem">-reg2mem: Demote all values to stack slots</a>
+</h3>
+<div>
<p>
This file demotes all registers to memory references. It is intented to be
the inverse of <a href="#mem2reg"><tt>-mem2reg</tt></a>. By converting to
- <tt>load</tt> instructions, the only values live accross basic blocks are
+ <tt>load</tt> instructions, the only values live across basic blocks are
<tt>alloca</tt> instructions and <tt>load</tt> instructions before
<tt>phi</tt> nodes. It is intended that this should make CFG hacking much
easier. To make later hacking easier, the entry block is split into two, such
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="scalarrepl">Scalar Replacement of Aggregates</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="scalarrepl">-scalarrepl: Scalar Replacement of Aggregates (DT)</a>
+</h3>
+<div>
<p>
The well-known scalar replacement of aggregates transformation. This
transform breaks up <tt>alloca</tt> instructions of aggregate type (structure
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="sccp">Sparse Conditional Constant Propagation</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="sccp">-sccp: Sparse Conditional Constant Propagation</a>
+</h3>
+<div>
<p>
Sparse conditional constant propagation and merging, which can be summarized
as:
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="simplify-libcalls">Simplify well-known library calls</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="simplify-libcalls">-simplify-libcalls: Simplify well-known library calls</a>
+</h3>
+<div>
<p>
Applies a variety of small optimizations for calls to specific well-known
function calls (e.g. runtime library functions). For example, a call
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="simplifycfg">Simplify the CFG</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="simplifycfg">-simplifycfg: Simplify the CFG</a>
+</h3>
+<div>
<p>
Performs dead code elimination and basic block merging. Specifically:
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="strip">Strip all symbols from a module</a>
+<h3>
+ <a name="sink">-sink: Code sinking</a>
+</h3>
+<div>
+ <p>This pass moves instructions into successor blocks, when possible, so that
+ they aren't executed on paths where their results aren't needed.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="sretpromotion">-sretpromotion: Promote sret arguments to multiple ret values</a>
+</h3>
+<div>
+ <p>
+ This pass finds functions that return a struct (using a pointer to the struct
+ as the first argument of the function, marked with the '<tt>sret</tt>' attribute) and
+ replaces them with a new function that simply returns each of the elements of
+ that struct (using multiple return values).
+ </p>
+
+ <p>
+ This pass works under a number of conditions:
+ </p>
+
+ <ul>
+ <li>The returned struct must not contain other structs</li>
+ <li>The returned struct must only be used to load values from</li>
+ <li>The placeholder struct passed in is the result of an <tt>alloca</tt></li>
+ </ul>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip">-strip: Strip all symbols from a module</a>
+</h3>
+<div>
+ <p>
+ performs code stripping. this transformation can delete:
+ </p>
+
+ <ol>
+ <li>names for virtual registers</li>
+ <li>symbols for internal globals and functions</li>
+ <li>debug information</li>
+ </ol>
+
+ <p>
+ note that this transformation makes code much less readable, so it should
+ only be used in situations where the <tt>strip</tt> utility would be used,
+ such as reducing code size or making it harder to reverse engineer code.
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip-dead-debug-info">-strip-dead-debug-info: Strip debug info for unused symbols</a>
+</h3>
+<div>
<p>
- Performs code stripping. This transformation can delete:
+ performs code stripping. this transformation can delete:
</p>
<ol>
</ol>
<p>
- Note that this transformation makes code much less readable, so it should
+ note that this transformation makes code much less readable, so it should
only be used in situations where the <tt>strip</tt> utility would be used,
such as reducing code size or making it harder to reverse engineer code.
</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="tailcallelim">Tail Call Elimination</a>
+<h3>
+ <a name="strip-dead-prototypes">-strip-dead-prototypes: Strip Unused Function Prototypes</a>
+</h3>
+<div>
+ <p>
+ This pass loops over all of the functions in the input module, looking for
+ dead declarations and removes them. Dead declarations are declarations of
+ functions for which no implementation is available (i.e., declarations for
+ unused library functions).
+ </p>
</div>
-<div class="doc_text">
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip-debug-declare">-strip-debug-declare: Strip all llvm.dbg.declare intrinsics</a>
+</h3>
+<div>
+ <p>This pass implements code stripping. Specifically, it can delete:</p>
+ <ul>
+ <li>names for virtual registers</li>
+ <li>symbols for internal globals and functions</li>
+ <li>debug information</li>
+ </ul>
+ <p>
+ Note that this transformation makes code much less readable, so it should
+ only be used in situations where the 'strip' utility would be used, such as
+ reducing code size or making it harder to reverse engineer code.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="strip-nondebug">-strip-nondebug: Strip all symbols, except dbg symbols, from a module</a>
+</h3>
+<div>
+ <p>This pass implements code stripping. Specifically, it can delete:</p>
+ <ul>
+ <li>names for virtual registers</li>
+ <li>symbols for internal globals and functions</li>
+ <li>debug information</li>
+ </ul>
+ <p>
+ Note that this transformation makes code much less readable, so it should
+ only be used in situations where the 'strip' utility would be used, such as
+ reducing code size or making it harder to reverse engineer code.
+ </p>
+</div>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="tailcallelim">-tailcallelim: Tail Call Elimination</a>
+</h3>
+<div>
<p>
This file transforms calls of the current function (self recursion) followed
by a return instruction with a branch to the entry of the function, creating
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="tailduplicate">Tail Duplication</a>
-</div>
-<div class="doc_text">
+<h3>
+ <a name="tailduplicate">-tailduplicate: Tail Duplication</a>
+</h3>
+<div>
<p>
This pass performs a limited form of tail duplication, intended to simplify
CFGs by removing some unconditional branches. This pass is necessary to
</p>
</div>
+</div>
+
<!-- ======================================================================= -->
-<div class="doc_section"> <a name="transform">Utility Passes</a></div>
-<div class="doc_text">
+<h2><a name="utilities">Utility Passes</a></h2>
+<div>
<p>This section describes the LLVM Utility Passes.</p>
-</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="deadarghaX0r">Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
+<h3>
+ <a name="deadarghaX0r">-deadarghaX0r: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)</a>
+</h3>
+<div>
+ <p>
+ Same as dead argument elimination, but deletes arguments to functions which
+ are external. This is only for use by <a
+ href="Bugpoint.html">bugpoint</a>.</p>
</div>
-<div class="doc_text">
- <p>Yet to be written.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="extract-blocks">-extract-blocks: Extract Basic Blocks From Module (for bugpoint use)</a>
+</h3>
+<div>
+ <p>
+ This pass is used by bugpoint to extract all blocks from the module into their
+ own functions.</p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="extract-blocks">Extract Basic Blocks From Module (for bugpoint use)</a>
+<h3>
+ <a name="instnamer">-instnamer: Assign names to anonymous instructions</a>
+</h3>
+<div>
+ <p>This is a little utility pass that gives instructions names, this is mostly
+ useful when diffing the effect of an optimization because deleting an
+ unnamed instruction can change all other instruction numbering, making the
+ diff very noisy.
+ </p>
</div>
-<div class="doc_text">
- <p>Yet to be written.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="preverify">-preverify: Preliminary module verification</a>
+</h3>
+<div>
+ <p>
+ Ensures that the module is in the form required by the <a
+ href="#verifier">Module Verifier</a> pass.
+ </p>
+
+ <p>
+ Running the verifier runs this pass automatically, so there should be no need
+ to use it directly.
+ </p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="emitbitcode">Bitcode Writer</a>
+<h3>
+ <a name="verify">-verify: Module Verifier</a>
+</h3>
+<div>
+ <p>
+ Verifies an LLVM IR code. This is useful to run after an optimization which is
+ undergoing testing. Note that <tt>llvm-as</tt> verifies its input before
+ emitting bitcode, and also that malformed bitcode is likely to make LLVM
+ crash. All language front-ends are therefore encouraged to verify their output
+ before performing optimizing transformations.
+ </p>
+
+ <ul>
+ <li>Both of a binary operator's parameters are of the same type.</li>
+ <li>Verify that the indices of mem access instructions match other
+ operands.</li>
+ <li>Verify that arithmetic and other things are only performed on
+ first-class types. Verify that shifts and logicals only happen on
+ integrals f.e.</li>
+ <li>All of the constants in a switch statement are of the correct type.</li>
+ <li>The code is in valid SSA form.</li>
+ <li>It is illegal to put a label into any other type (like a structure) or
+ to return one.</li>
+ <li>Only phi nodes can be self referential: <tt>%x = add i32 %x, %x</tt> is
+ invalid.</li>
+ <li>PHI nodes must have an entry for each predecessor, with no extras.</li>
+ <li>PHI nodes must be the first thing in a basic block, all grouped
+ together.</li>
+ <li>PHI nodes must have at least one entry.</li>
+ <li>All basic blocks should only end with terminator insts, not contain
+ them.</li>
+ <li>The entry node to a function must not have predecessors.</li>
+ <li>All Instructions must be embedded into a basic block.</li>
+ <li>Functions cannot take a void-typed parameter.</li>
+ <li>Verify that a function's argument list agrees with its declared
+ type.</li>
+ <li>It is illegal to specify a name for a void value.</li>
+ <li>It is illegal to have a internal global value with no initializer.</li>
+ <li>It is illegal to have a ret instruction that returns a value that does
+ not agree with the function return value type.</li>
+ <li>Function call argument types match the function prototype.</li>
+ <li>All other things that are tested by asserts spread about the code.</li>
+ </ul>
+
+ <p>
+ Note that this does not provide full security verification (like Java), but
+ instead just tries to ensure that code is well-formed.
+ </p>
</div>
-<div class="doc_text">
- <p>Yet to be written.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-cfg">-view-cfg: View CFG of function</a>
+</h3>
+<div>
+ <p>
+ Displays the control flow graph using the GraphViz tool.
+ </p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="verify">Module Verifier</a>
+<h3>
+ <a name="view-cfg-only">-view-cfg-only: View CFG of function (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ Displays the control flow graph using the GraphViz tool, but omitting function
+ bodies.
+ </p>
</div>
-<div class="doc_text">
- <p>Yet to be written.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-dom">-view-dom: View dominance tree of function</a>
+</h3>
+<div>
+ <p>
+ Displays the dominator tree using the GraphViz tool.
+ </p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="view-cfg">View CFG of function</a>
+<h3>
+ <a name="view-dom-only">-view-dom-only: View dominance tree of function (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ Displays the dominator tree using the GraphViz tool, but omitting function
+ bodies.
+ </p>
</div>
-<div class="doc_text">
- <p>Yet to be written.</p>
+
+<!-------------------------------------------------------------------------- -->
+<h3>
+ <a name="view-postdom">-view-postdom: View postdominance tree of function</a>
+</h3>
+<div>
+ <p>
+ Displays the post dominator tree using the GraphViz tool.
+ </p>
</div>
<!-------------------------------------------------------------------------- -->
-<div class="doc_subsection">
- <a name="view-cfg-only">View CFG of function (with no function bodies)</a>
+<h3>
+ <a name="view-postdom-only">-view-postdom-only: View postdominance tree of function (with no function bodies)</a>
+</h3>
+<div>
+ <p>
+ Displays the post dominator tree using the GraphViz tool, but omitting
+ function bodies.
+ </p>
</div>
-<div class="doc_text">
- <p>Yet to be written.</p>
+
</div>
<!-- *********************************************************************** -->
<hr>
<address>
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
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- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
+ src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
<a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
- <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
+ <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
</address>
projects / oota-llvm.git / blobdiff