X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=docs%2FPasses.html;h=840b2eff0647babc7c86c2b969a2e91aae1c666d;hb=cff391a8251c12b57f56fc17fb69327c173b5a03;hp=8c086720a8bb731b8530b5e08ea20c1d007e2fbe;hpb=444087057ad0592f3e0bb2e434e0b610aa7914f6;p=oota-llvm.git diff --git a/docs/Passes.html b/docs/Passes.html index 8c086720a8b..840b2eff064 100644 --- a/docs/Passes.html +++ b/docs/Passes.html @@ -27,7 +27,7 @@ while () { my $o = $order{$1}; $o = "000" unless defined $o; push @x, "$o-$1$2\n"; - push @y, "$o $2\n"; + push @y, "$o -$1: $2\n"; } @x = map { s/^\d\d\d//; $_ } sort @x; @y = map { s/^\d\d\d//; $_ } sort @y; @@ -40,7 +40,7 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

\n" if ! --> -

LLVM's Analysis and Transform Passes
+

LLVM's Analysis and Transform Passes

  1. Introduction
    2. @@ -55,8 +55,8 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if ! -

    Introduction
    -
    +

    Introduction

    +

    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. @@ -69,17 +69,13 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if ! bitcode are neither analysis nor transform passes.

    The table below provides a quick summary of each pass and links to the more complete pass description later in the document.

    -
    -
    + - - + - - @@ -87,12 +83,21 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    + + + + - - + + + + + + + @@ -101,23 +106,30 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    + + + + + + + + - - + @@ -125,54 +137,51 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    - + - - - - - - + - + - + - + - - + - - + + - + - - + + + - - + + + + @@ -181,24 +190,29 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    + + + + +
    ANALYSIS PASSES
    OptionName
    -aa-evalExhaustive Alias Analysis Precision Evaluator
    -anders-aaAndersen's Interprocedural Alias Analysis
    -basicaaBasic Alias Analysis (default AA impl)
    -basicaaBasic Alias Analysis (stateless AA impl)
    -basiccgBasic CallGraph Construction
    -basicvnBasic Value Numbering (default GVN impl)
    -codegenprepareOptimize for code generation
    -count-aaCount Alias Analysis Query Responses
    -debug-aaAA use debugger
    -domfrontierDominance Frontier Construction
    -dot-callgraphPrint Call Graph to 'dot' file
    -dot-cfgPrint CFG of function to 'dot' file
    -dot-cfg-onlyPrint CFG of function to 'dot' file (with no function bodies)
    -dot-domPrint dominance tree of function to 'dot' file
    -dot-dom-onlyPrint dominance tree of function to 'dot' file (with no function bodies)
    -dot-postdomPrint postdominance tree of function to 'dot' file
    -dot-postdom-onlyPrint postdominance tree of function to 'dot' file (with no function bodies)
    -globalsmodref-aaSimple mod/ref analysis for globals
    -instcountCounts the various types of Instructions
    -intervalsInterval Partition Construction
    -load-vnLoad Value Numbering
    -loopsNatural Loop Construction
    -iv-usersInduction Variable Users
    -lazy-value-infoLazy Value Information Analysis
    -ldaLoop Dependence Analysis
    -libcall-aaLibCall Alias Analysis
    -lintStatically lint-checks LLVM IR
    -loopsNatural Loop Information
    -memdepMemory Dependence Analysis
    -module-debuginfoDecodes module-level debug info
    -no-aaNo Alias Analysis (always returns 'may' alias)
    -no-profileNo Profile Information
    -postdomfrontierPost-Dominance Frontier Construction
    -print-callgraphPrint a call graph
    -print-callgraph-sccsPrint SCCs of the Call Graph
    -print-cfg-sccsPrint SCCs of each function CFG
    -print-dbginfoPrint debug info in human readable form
    -print-dom-infoDominator Info Printer
    -print-externalfnconstantsPrint external fn callsites passed constants
    -print-functionPrint function to stderr
    -print-modulePrint module to stderr
    -print-used-typesFind Used Types
    -profile-estimatorEstimate profiling information
    -profile-loaderLoad profile information from llvmprof.out
    -profile-verifierVerify profiling information
    -regionsDetect single entry single exit regions
    -scalar-evolutionScalar Evolution Analysis
    -scev-aaScalarEvolution-based Alias Analysis
    -targetdataTarget Data Layout
    TRANSFORM PASSES
    OptionName
    -adceAggressive Dead Code Elimination
    -always-inlineInliner for always_inline functions
    -argpromotionPromote 'by reference' arguments to scalars
    -bb-vectorizeCombine instructions to form vector instructions within basic blocks
    -block-placementProfile Guided Basic Block Placement
    -break-crit-edgesBreak critical edges in CFG
    -codegenpreparePrepare a function for code generation
    -condpropConditional Propagation
    -codegenprepareOptimize for code generation
    -constmergeMerge Duplicate Global Constants
    -constpropSimple constant propagation
    -dceDead Code Elimination
    -deadtypeelimDead Type Elimination
    -dieDead Instruction Elimination
    -dseDead Store Elimination
    -gcseGlobal Common Subexpression Elimination
    -functionattrsDeduce function attributes
    -globaldceDead Global Elimination
    -globaloptGlobal Variable Optimizer
    -gvnGlobal Value Numbering
    -gvnpreGlobal Value Numbering/Partial Redundancy Elimination
    -indmemremIndirect Malloc and Free Removal
    -indvarsCanonicalize Induction Variables
    -inlineFunction Integration/Inlining
    -insert-block-profilingInsert instrumentation for block profiling
    -insert-edge-profilingInsert instrumentation for edge profiling
    -insert-function-profilingInsert instrumentation for function profiling
    -insert-null-profiling-rsMeasure profiling framework overhead
    -insert-rs-profiling-frameworkInsert random sampling instrumentation framework
    -insert-optimal-edge-profilingInsert optimal instrumentation for edge profiling
    -instcombineCombine redundant instructions
    -internalizeInternalize Global Symbols
    -ipconstpropInterprocedural constant propagation
    -ipsccpInterprocedural Sparse Conditional Constant Propagation
    -jump-threadingThread control through conditional blocks
    -jump-threadingJump Threading
    -lcssaLoop-Closed SSA Form Pass
    -licmLoop Invariant Code Motion
    -loop-deletionDead Loop Deletion Pass
    -loop-deletionDelete dead loops
    -loop-extractExtract loops into new functions
    -loop-extract-singleExtract at most one loop into a new function
    -loop-index-splitIndex Split Loops
    -loop-reduceLoop Strength Reduction
    -loop-rotateRotate Loops
    -loop-simplifyCanonicalize natural loops
    -loop-unrollUnroll loops
    -loop-unswitchUnswitch loops
    -loopsimplifyCanonicalize natural loops
    -lowerallocsLower allocations from instructions to calls
    -loweratomicLower atomic intrinsics to non-atomic form
    -lowerinvokeLower invoke and unwind, for unwindless code generators
    -lowersetjmpLower Set Jump
    -lowerswitchLower SwitchInst's to branches
    -mem2regPromote Memory to Register
    -memcpyoptOptimize use of memcpy and friends
    -memcpyoptMemCpy Optimization
    -mergefuncMerge Functions
    -mergereturnUnify function exit nodes
    -predsimplifyPredicate Simplifier
    -partial-inlinerPartial Inliner
    -prune-ehRemove unused exception handling info
    -raiseallocsRaise allocations from calls to instructions
    -reassociateReassociate expressions
    -reg2memDemote all values to stack slots
    -scalarreplScalar Replacement of Aggregates
    -scalarreplScalar Replacement of Aggregates (DT)
    -sccpSparse Conditional Constant Propagation
    -simplify-libcallsSimplify well-known library calls
    -simplifycfgSimplify the CFG
    -sinkCode sinking
    -sretpromotionPromote sret arguments to multiple ret values
    -stripStrip all symbols from a module
    -strip-dead-prototypesRemove unused function declarations
    -sretpromotionPromote sret arguments
    -strip-dead-debug-infoStrip debug info for unused symbols
    -strip-dead-prototypesStrip Unused Function Prototypes
    -strip-debug-declareStrip all llvm.dbg.declare intrinsics
    -strip-nondebugStrip all symbols, except dbg symbols, from a module
    -tailcallelimTail Call Elimination
    -tailduplicateTail Duplication
    OptionName
    -deadarghaX0rDead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE)
    -extract-blocksExtract Basic Blocks From Module (for bugpoint use)
    -instnamerAssign names to anonymous instructions
    -preverifyPreliminary module verification
    -verifyModule Verifier
    -view-cfgView CFG of function
    -view-cfg-onlyView CFG of function (with no function bodies)
    -view-domView dominance tree of function
    -view-dom-onlyView dominance tree of function (with no function bodies)
    -view-postdomView postdominance tree of function
    -view-postdom-onlyView postdominance tree of function (with no function bodies)
    +
    -
    Analysis Passes
    -
    +

    Analysis Passes

    +

    This section describes the LLVM Analysis Passes.

    -
    -
    - Exhaustive Alias Analysis Precision Evaluator -
    -
    +

    + -aa-eval: Exhaustive Alias Analysis Precision Evaluator +

    +

    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 @@ -209,129 +223,27 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Andersen's Interprocedural Alias Analysis -
    -
    -

    - This is an implementation of Andersen's interprocedural alias - analysis -

    - -

    - In pointer analysis terms, this is a subset-based, flow-insensitive, - field-sensitive, and context-insensitive algorithm pointer algorithm. -

    - -

    - This algorithm is implemented as three stages: -

    - -
      -
    1. Object identification.
      2. -
    2. Inclusion constraint identification.
      3. -
    3. Offline constraint graph optimization.
      4. -
    4. Inclusion constraint solving.
      5. -
    - -

    - The object identification stage identifies all of the memory objects in the - program, which includes globals, heap allocated objects, and stack allocated - objects. -

    - -

    - 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 - A = B, this statement is processed to - indicate that A can point to anything that B can point - to. Constraints can handle copies, loads, and stores, and address taking. -

    - -

    - 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. -

    - -

    - The inclusion constraint solving phase iteratively propagates the inclusion - constraints until a fixed point is reached. This is an O(n³) - algorithm. -

    - -

    - Function constraints are handled as if they were structs with X - fields. Thus, an access to argument X of function Y is - an access to node index getNode(Y) + X. - This representation allows handling of indirect calls without any issues. To - wit, an indirect call Y(a,b) is - equivalent to *(Y + 1) = a, *(Y + 2) = - b. The return node for a function F is always - located at getNode(F) + CallReturnPos. The arguments - start at getNode(F) + CallArgPos. -

    -
    - - -
    - Basic Alias Analysis (default AA impl) -
    -
    -

    - This is the default implementation of the Alias Analysis interface - that simply implements a few identities (two different globals cannot alias, - etc), but otherwise does no analysis. -

    +

    + -basicaa: Basic Alias Analysis (stateless AA impl) +

    +
    +

    A basic alias analysis pass that implements identities (two different + globals cannot alias, etc), but does no stateful analysis.

    -
    - Basic CallGraph Construction -
    -
    +

    + -basiccg: Basic CallGraph Construction +

    +

    Yet to be written.

    -
    - Basic Value Numbering (default Value Numbering impl) -
    -
    -

    - This is the default implementation of the ValueNumbering - 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. -

    -

    - The ValueNumbering analysis passes are mostly deprecated. They are only used - by the Global Common Subexpression Elimination pass, which - is deprecated by the Global Value Numbering pass (which - does its value numbering on its own). -

    -
    - - -
    - Optimize for code generation -
    -
    -

    - 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. -

    -
    - - -
    - Count Alias Analysis Query Responses -
    -
    +

    + -count-aa: Count Alias Analysis Query Responses +

    +

    A pass which can be used to count how many alias queries are being made and how the alias analysis implementation being used responds. @@ -339,10 +251,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - AA use debugger -
    -
    +

    + -debug-aa: AA use debugger +

    +

    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. @@ -356,10 +268,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Dominance Frontier Construction -
    -
    +

    + -domfrontier: Dominance Frontier Construction +

    +

    This pass is a simple dominator construction algorithm for finding forward dominator frontiers. @@ -367,10 +279,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Dominator Tree Construction -
    -
    +

    + -domtree: Dominator Tree Construction +

    +

    This pass is a simple dominator construction algorithm for finding forward dominators. @@ -378,10 +290,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Print Call Graph to 'dot' file -
    -
    +

    + -dot-callgraph: Print Call Graph to 'dot' file +

    +

    This pass, only available in opt, prints the call graph into a .dot graph. This graph can then be processed with the "dot" tool @@ -390,10 +302,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Print CFG of function to 'dot' file -
    -
    +

    + -dot-cfg: Print CFG of function to 'dot' file +

    +

    This pass, only available in opt, prints the control flow graph into a .dot graph. This graph can then be processed with the @@ -402,10 +314,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Print CFG of function to 'dot' file (with no function bodies) -
    -
    +

    + -dot-cfg-only: Print CFG of function to 'dot' file (with no function bodies) +

    +

    This pass, only available in opt, prints the control flow graph into a .dot graph, omitting the function bodies. This graph can @@ -415,10 +327,60 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Simple mod/ref analysis for globals +

    + -dot-dom: Print dominance tree of function to 'dot' file +

    +
    +

    + This pass, only available in opt, prints the dominator tree + into a .dot graph. This graph can then be processed with the + "dot" tool to convert it to postscript or some other suitable format. +

    +
    + + +

    + -dot-dom-only: Print dominance tree of function to 'dot' file (with no function bodies) +

    +
    +

    + This pass, only available in opt, prints the dominator tree + into a .dot 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. +

    +
    + + +

    + -dot-postdom: Print postdominance tree of function to 'dot' file +

    +
    +

    + This pass, only available in opt, prints the post dominator tree + into a .dot graph. This graph can then be processed with the + "dot" tool to convert it to postscript or some other suitable format. +

    -
    + + +

    + -dot-postdom-only: Print postdominance tree of function to 'dot' file (with no function bodies) +

    +
    +

    + This pass, only available in opt, prints the post dominator tree + into a .dot 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. +

    +
    + + +

    + -globalsmodref-aa: Simple mod/ref analysis for globals +

    +

    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 @@ -428,20 +390,20 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Counts the various types of Instructions -
    -
    +

    + -instcount: Counts the various types of Instructions +

    +

    This pass collects the count of all instructions and reports them

    -
    - Interval Partition Construction -
    -
    +

    + -intervals: Interval Partition Construction +

    +

    This analysis calculates and represents the interval partition of a function, or a preexisting interval partition. @@ -454,32 +416,75 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Load Value Numbering +

    + -iv-users: Induction Variable Users +

    +
    +

    Bookkeeping for "interesting" users of expressions computed from + induction variables.

    -
    -

    - 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. -

    + + +

    + -lazy-value-info: Lazy Value Information Analysis +

    +
    +

    Interface for lazy computation of value constraint information.

    +
    + + +

    + -lda: Loop Dependence Analysis +

    +
    +

    Loop dependence analysis framework, which is used to detect dependences in + memory accesses in loops.

    +
    + + +

    + -libcall-aa: LibCall Alias Analysis +

    +
    +

    LibCall Alias Analysis.

    +
    + + +

    + -lint: Statically lint-checks LLVM IR +

    +
    +

    This pass statically checks for common and easily-identified constructs + which produce undefined or likely unintended behavior in LLVM IR.

    + +

    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.

    -

    - 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. +

    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.

    + +

    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.

    + +

    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.

    -
    - Natural Loop Construction -
    -
    +

    + -loops: Natural Loop Information +

    +

    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 @@ -489,10 +494,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Memory Dependence Analysis -
    -
    +

    + -memdep: Memory Dependence Analysis +

    +

    An analysis that determines, for a given memory operation, what preceding memory operations it depends on. It builds on alias analysis information, and @@ -502,22 +507,36 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - No Alias Analysis (always returns 'may' alias) +

    + -module-debuginfo: Decodes module-level debug info +

    +
    +

    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. +

    -
    + + +

    + -no-aa: No Alias Analysis (always returns 'may' alias) +

    +

    - 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 - such it doesn't follow many of the rules that other alias analyses must. + This is the default implementation of the Alias Analysis interface. It 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 such it + doesn't follow many of the rules that other alias analyses must.

    -
    - No Profile Information -
    -
    +

    + -no-profile: No Profile Information +

    +

    The default "no profile" implementation of the abstract ProfileInfo interface. @@ -525,10 +544,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Post-Dominance Frontier Construction -
    -
    +

    + -postdomfrontier: Post-Dominance Frontier Construction +

    +

    This pass is a simple post-dominator construction algorithm for finding post-dominator frontiers. @@ -536,10 +555,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Post-Dominator Tree Construction -
    -
    +

    + -postdomtree: Post-Dominator Tree Construction +

    +

    This pass is a simple post-dominator construction algorithm for finding post-dominators. @@ -547,51 +566,73 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Alias Set Printer -
    -
    +

    + -print-alias-sets: Alias Set Printer +

    +

    Yet to be written.

    -
    - Print a call graph -
    -
    +

    + -print-callgraph: Print a call graph +

    +

    This pass, only available in opt, prints the call graph to - standard output in a human-readable form. + standard error in a human-readable form.

    -
    - Print SCCs of the Call Graph -
    -
    +

    + -print-callgraph-sccs: Print SCCs of the Call Graph +

    +

    This pass, only available in opt, prints the SCCs of the call - graph to standard output in a human-readable form. + graph to standard error in a human-readable form.

    -
    - Print SCCs of each function CFG -
    -
    +

    + -print-cfg-sccs: Print SCCs of each function CFG +

    +

    This pass, only available in opt, prints the SCCs of each - function CFG to standard output in a human-readable form. + function CFG to standard error in a human-readable form.

    -
    - Print external fn callsites passed constants +

    + -print-dbginfo: Print debug info in human readable form +

    +
    +

    Pass that prints instructions, and associated debug info:

    +
      + +
    • source/line/col information
      • +
    • original variable name
      • +
    • original type name
      • +
    +
    + + +

    + -print-dom-info: Dominator Info Printer +

    +
    +

    Dominator Info Printer.

    -
    + + +

    + -print-externalfnconstants: Print external fn callsites passed constants +

    +

    This pass, only available in opt, prints out call sites to external functions that are called with constant arguments. This can be @@ -601,10 +642,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Print function to stderr -
    -
    +

    + -print-function: Print function to stderr +

    +

    The PrintFunctionPass class is designed to be pipelined with other FunctionPasses, and prints out the functions of the module @@ -613,20 +654,20 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Print module to stderr -
    -
    +

    + -print-module: Print module to stderr +

    +

    This pass simply prints out the entire module when it is executed.

    -
    - Find Used Types -
    -
    +

    + -print-used-types: Find Used Types +

    +

    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 @@ -634,10 +675,20 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Load profile information from llvmprof.out +

    + -profile-estimator: Estimate profiling information +

    +
    +

    Profiling information that estimates the profiling information + in a very crude and unimaginative way. +

    -
    + + +

    + -profile-loader: Load profile information from llvmprof.out +

    +

    A concrete implementation of profiling information that loads the information from a profile dump file. @@ -645,10 +696,29 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Scalar Evolution Analysis +

    + -profile-verifier: Verify profiling information +

    +
    +

    Pass that checks profiling information for plausibility.

    +
    +

    + -regions: Detect single entry single exit regions +

    +
    +

    + The RegionInfo 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. +

    -
    + + +

    + -scalar-evolution: Scalar Evolution Analysis +

    +

    The ScalarEvolution analysis can be used to analyze and catagorize scalar expressions in loops. It specializes in recognizing general @@ -664,25 +734,42 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Target Data Layout +

    + -scev-aa: ScalarEvolution-based Alias Analysis +

    +
    +

    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. +

    -
    + + +

    + -targetdata: Target Data Layout +

    +

    Provides other passes access to information on how the size and alignment required by the the target ABI for various data types.

    +
    + -
    Transform Passes
    -
    +

    Transform Passes

    +

    This section describes the LLVM Transform Passes.

    -
    -
    - Aggressive Dead Code Elimination -
    -
    +

    + -adce: Aggressive Dead Code Elimination +

    +

    ADCE aggressively tries to eliminate code. This pass is similar to DCE but it assumes that values are dead until proven otherwise. This is similar to SCCP, except applied to @@ -690,10 +777,19 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Promote 'by reference' arguments to scalars +

    + -always-inline: Inliner for always_inline functions +

    +
    +

    A custom inliner that handles only functions that are marked as + "always inline".

    -
    + + +

    + -argpromotion: Promote 'by reference' arguments to scalars +

    +

    This pass promotes "by reference" arguments to be "by value" arguments. In practice, this means looking for internal functions that have pointer @@ -721,10 +817,30 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Profile Guided Basic Block Placement +

    + -bb-vectorize: Basic-Block Vectorization +

    +
    +

    This pass combines instructions inside basic blocks to form vector + instructions. It iterates over each basic block, attempting to pair + compatible instructions, repeating this process until no additional + pairs are selected for vectorization. When the outputs of some pair + of compatible instructions are used as inputs by some other pair of + compatible instructions, those pairs are part of a potential + vectorization chain. Instruction pairs are only fused into vector + instructions when they are part of a chain longer than some + threshold length. Moreover, the pass attempts to find the best + possible chain for each pair of compatible instructions. These + heuristics are intended to prevent vectorization in cases where + it would not yield a performance increase of the resulting code. +

    -
    + + +

    + -block-placement: Profile Guided Basic Block Placement +

    +

    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 @@ -733,10 +849,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Break critical edges in CFG -
    -
    +

    + -break-crit-edges: Break critical edges in CFG +

    +

    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 @@ -746,29 +862,20 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Prepare a function for code generation -
    -
    +

    + -codegenprepare: Optimize for code generation +

    +
    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.
    -
    - Conditional Propagation -
    -
    -

    This pass propagates information about conditional expressions through the - program, allowing it to eliminate conditional branches in some cases.

    -
    - - -
    - Merge Duplicate Global Constants -
    -
    +

    + -constmerge: Merge Duplicate Global Constants +

    +

    Merges duplicate global constants together into a single constant that is shared. This is useful because some passes (ie TraceValues) insert a lot of @@ -778,10 +885,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Simple constant propagation -
    -
    +

    + -constprop: Simple constant propagation +

    +

    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:

    @@ -794,10 +901,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Dead Code Elimination -
    -
    +

    + -dce: Dead Code Elimination +

    +

    Dead code elimination is similar to dead instruction elimination, but it rechecks instructions that were used by removed @@ -806,10 +913,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Dead Argument Elimination -
    -
    +

    + -deadargelim: Dead Argument Elimination +

    +

    This pass deletes dead arguments from internal functions. Dead argument elimination removes arguments which are directly dead, as well as arguments @@ -824,10 +931,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Dead Type Elimination -
    -
    +

    + -deadtypeelim: Dead Type Elimination +

    +

    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 )) { s:^ *///? ?::; print "

    \n" if !

    -
    - Dead Instruction Elimination -
    -
    +

    + -die: Dead Instruction Elimination +

    +

    Dead instruction elimination performs a single pass over the function, removing instructions that are obviously dead. @@ -847,10 +954,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Dead Store Elimination -
    -
    +

    + -dse: Dead Store Elimination +

    +

    A trivial dead store elimination that only considers basic-block local redundant stores. @@ -858,27 +965,25 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Global Common Subexpression Elimination -
    -
    -

    - 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 analysis pass to identify the common - subexpressions, eliminating them when possible. -

    -

    - This pass is deprecated by the Global Value Numbering pass - (which does a better job with its own value numbering). +

    + -functionattrs: Deduce function attributes +

    +
    +

    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.

    -
    - Dead Global Elimination -
    -
    +

    + -globaldce: Dead Global Elimination +

    +

    This transform is designed to eliminate unreachable internal globals from the program. It uses an aggressive algorithm, searching out globals that are @@ -889,10 +994,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Global Variable Optimizer -
    -
    +

    + -globalopt: Global Variable Optimizer +

    +

    This pass transforms simple global variables that never have their address taken. If obviously true, it marks read/write globals as constant, deletes @@ -901,63 +1006,21 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Global Value Numbering -
    -
    -

    - This pass performs global value numbering to eliminate fully redundant - instructions. It also performs simple dead load elimination. -

    -

    - Note that this pass does the value numbering itself, it does not use the - ValueNumbering analysis passes. -

    -
    - - -
    - Global Value Numbering/Partial Redundancy Elimination -
    -
    -

    - 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. -

    -

    - Note that this pass does the value numbering itself, it does not use the - ValueNumbering analysis passes. -

    -
    - - -
    - Indirect Malloc and Free Removal -
    -
    -

    - 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. -

    - +

    + -gvn: Global Value Numbering +

    +

    - Thus find places where the address of memory functions are taken and construct - bounce functions with direct calls of those functions. + This pass performs global value numbering to eliminate fully and partially + redundant instructions. It also performs redundant load elimination.

    -
    - Canonicalize Induction Variables -
    -
    +

    + -indvars: Canonicalize Induction Variables +

    +

    This transformation analyzes and transforms the induction variables (and computations derived from them) into simpler forms suitable for subsequent @@ -1005,39 +1068,20 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Function Integration/Inlining -
    -
    +

    + -inline: Function Integration/Inlining +

    +

    Bottom-up inlining of functions into callees.

    -
    - Insert instrumentation for block profiling -
    -
    -

    - 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. -

    - -

    - 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. -

    -
    - - -
    - Insert instrumentation for edge profiling -
    -
    +

    + -insert-edge-profiling: Insert instrumentation for edge profiling +

    +

    This pass instruments the specified program with counters for edge profiling. Edge profiling can give a reasonable approximation of the hot paths through a @@ -1052,54 +1096,21 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Insert instrumentation for function profiling -
    -
    -

    - This pass instruments the specified program with counters for function - profiling, which counts the number of times each function is called. -

    -
    - - -
    - Measure profiling framework overhead -
    -
    -

    - The basic profiler that does nothing. It is the default profiler and thus - terminates RSProfiler chains. It is useful for measuring - framework overhead. -

    -
    - - -
    - Insert random sampling instrumentation framework -
    -
    -

    - 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. -

    - -

    - After this pass, it is highly recommended to runmem2reg - and adce. instcombine, - load-vn, gdce, and - dse also are good to run afterwards. +

    + -insert-optimal-edge-profiling: Insert optimal instrumentation for edge profiling +

    +
    +

    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.

    -
    - Combine redundant instructions -
    -
    +

    + -instcombine: Combine redundant instructions +

    +

    Combine instructions to form fewer, simple instructions. This pass does not modify the CFG This pass is where algebraic @@ -1150,10 +1161,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Internalize Global Symbols -
    -
    +

    + -internalize: Internalize Global Symbols +

    +

    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 @@ -1162,10 +1173,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Interprocedural constant propagation -
    -
    +

    + -ipconstprop: Interprocedural constant propagation +

    +

    This pass implements an extremely simple interprocedural constant propagation pass. It could certainly be improved in many different ways, @@ -1176,10 +1187,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Interprocedural Sparse Conditional Constant Propagation -
    -
    +

    + -ipsccp: Interprocedural Sparse Conditional Constant Propagation +

    +

    An interprocedural variant of Sparse Conditional Constant Propagation. @@ -1187,10 +1198,10 @@ perl -e '$/ = undef; for (split(/\n/, <>)) { s:^ *///? ?::; print "

    \n" if !

    -
    - Thread control through conditional blocks -
    -
    +

    + -jump-threading: Jump Threading +

    +

    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 @@ -1216,10 +1227,10 @@ if (X < 3) {

    -
    - Loop-Closed SSA Form Pass -
    -
    +

    + -lcssa: Loop-Closed SSA Form Pass +

    +

    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 @@ -1245,10 +1256,10 @@ if (X < 3) {

    -
    - Loop Invariant Code Motion -
    -
    +

    + -licm: Loop Invariant Code Motion +

    +

    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 @@ -1280,11 +1291,12 @@ if (X < 3) { variable.

    + -
    - Dead Loop Deletion Pass -
    -
    +

    + -loop-deletion: Delete dead loops +

    +

    This file implements the Dead Loop Deletion Pass. This pass is responsible for eliminating loops with non-infinite computable trip counts that have no @@ -1294,10 +1306,10 @@ if (X < 3) {

    -
    - Extract loops into new functions -
    -
    +

    + -loop-extract: Extract loops into new functions +

    +

    A pass wrapper around the ExtractLoop() scalar transformation to extract each top-level loop into its own new function. If the loop is the @@ -1307,10 +1319,10 @@ if (X < 3) {

    -
    - Extract at most one loop into a new function -
    -
    +

    + -loop-extract-single: Extract at most one loop into a new function +

    +

    Similar to Extract loops into new functions, this pass extracts one natural loop from the program into a function if it @@ -1319,21 +1331,10 @@ if (X < 3) {

    -
    - Index Split Loops -
    -
    -

    - This pass divides loop's iteration range by spliting loop such that each - individual loop is executed efficiently. -

    -
    - - -
    - Loop Strength Reduction -
    -
    +

    + -loop-reduce: Loop Strength Reduction +

    +

    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 @@ -1344,60 +1345,18 @@ if (X < 3) {

    -
    - Rotate Loops -
    -
    +

    + -loop-rotate: Rotate Loops +

    +

    A simple loop rotation transformation.

    -
    - Unroll loops -
    -
    -

    - This pass implements a simple loop unroller. It works best when loops have - been canonicalized by the -indvars pass, - allowing it to determine the trip counts of loops easily. -

    -
    - - -
    - Unswitch loops -
    -
    -

    - 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: -

    - - 
    for (...)                  if (lic)
-  A                          for (...)
-  if (lic)                     A; B; C
-    B                      else
-  C                          for (...)
-                               A; C
    - -

    - 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. -

    - -

    - This pass expects LICM to be run before it to hoist invariant conditions out - of the loop, to make the unswitching opportunity obvious. -

    -
    - - -
    - Canonicalize natural loops -
    -
    +

    + -loop-simplify: Canonicalize natural loops +

    +

    This pass performs several transformations to transform natural loops into a simpler form, which makes subsequent analyses and transformations simpler and @@ -1435,26 +1394,70 @@ if (X < 3) {

    -
    - Lower allocations from instructions to calls -
    -
    +

    + -loop-unroll: Unroll loops +

    +

    - Turn malloc and free instructions into @malloc and - @free calls. + This pass implements a simple loop unroller. It works best when loops have + been canonicalized by the -indvars pass, + allowing it to determine the trip counts of loops easily.

    +
    + +

    + -loop-unswitch: Unswitch loops +

    +
    +

    + 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: +

    + + 
    for (...)                  if (lic)
+  A                          for (...)
+  if (lic)                     A; B; C
+    B                      else
+  C                          for (...)
+                               A; C
    + +

    + 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. +

    +

    - This is a target-dependent tranformation because it depends on the size of - data types and alignment constraints. + This pass expects LICM to be run before it to hoist invariant conditions out + of the loop, to make the unswitching opportunity obvious.

    -
    - Lower invoke and unwind, for unwindless code generators +

    + -loweratomic: Lower atomic intrinsics to non-atomic form +

    +
    +

    + This pass lowers atomic intrinsics to non-atomic form for use in a known + non-preemptible environment. +

    + +

    + 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. +

    -
    + + +

    + -lowerinvoke: Lower invoke and unwind, for unwindless code generators +

    +

    This transformation is designed for use by code generators which do not yet support stack unwinding. This pass supports two models of exception handling @@ -1492,39 +1495,10 @@ if (X < 3) {

    -
    - Lower Set Jump -
    -
    -

    - Lowers setjmp and longjmp to use the LLVM invoke and unwind - instructions as necessary. -

    - -

    - Lowering of longjmp is fairly trivial. We replace the call with a - call to the LLVM library function __llvm_sjljeh_throw_longjmp(). - This unwinds the stack for us calling all of the destructors for - objects allocated on the stack. -

    - -

    - At a setjmp call, the basic block is split and the setjmp - removed. The calls in a function that have a setjmp are converted to - invoke where the except part checks to see if it's a longjmp - exception and, if so, if it's handled in the function. If it is, then it gets - the value returned by the longjmp and goes to where the basic block - was split. invoke instructions are handled in a similar fashion with - the original except block being executed if it isn't a longjmp - except that is handled by that function. -

    -
    - - -
    - Lower SwitchInst's to branches -
    -
    +

    + -lowerswitch: Lower SwitchInst's to branches +

    +

    Rewrites switch instructions with a sequence of branches, which allows targets to get away with not implementing the switch instruction until @@ -1533,10 +1507,10 @@ if (X < 3) {

    -
    - Promote Memory to Register -
    -
    +

    + -mem2reg: Promote Memory to Register +

    +

    This file promotes memory references to be register references. It promotes alloca instructions which only have loads and @@ -1549,10 +1523,10 @@ if (X < 3) {

    -
    - Optimize use of memcpy and friend -
    -
    +

    + -memcpyopt: MemCpy Optimization +

    +

    This pass performs various transformations related to eliminating memcpy calls, or transforming sets of stores into memset's. @@ -1560,10 +1534,31 @@ if (X < 3) {

    -
    - Unify function exit nodes +

    + -mergefunc: Merge Functions +

    +
    +

    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. +

    -
    + + +

    + -mergereturn: Unify function exit nodes +

    +

    Ensure that functions have at most one ret instruction in them. Additionally, it keeps track of which node is the new exit node of the CFG. @@ -1571,32 +1566,20 @@ if (X < 3) {

    -
    - Predicate Simplifier -
    -
    -

    - Path-sensitive optimizer. In a branch where x == y, replace uses of - x with y. Permits further optimization, such as the - elimination of the unreachable call: +

    + -partial-inliner: Partial Inliner +

    +
    +

    This pass performs partial inlining, typically by inlining an if + statement that surrounds the body of the function.

    - -
    void test(int *p, int *q)
-{
-  if (p != q)
-    return;
-
-  if (*p != *q)
-    foo(); // unreachable
-}
    -
    - Remove unused exception handling info -
    -
    +

    + -prune-eh: Remove unused exception handling info +

    +

    This file implements a simple interprocedural pass which walks the call-graph, turning invoke instructions into call instructions if and @@ -1606,21 +1589,10 @@ if (X < 3) {

    -
    - Raise allocations from calls to instructions -
    -
    -

    - Converts @malloc and @free calls to malloc and - free instructions. -

    -
    - - -
    - Reassociate expressions -
    -
    +

    + -reassociate: Reassociate expressions +

    +

    This pass reassociates commutative expressions in an order that is designed to promote better constant propagation, GCSE, LICM, PRE, etc. @@ -1640,14 +1612,14 @@ if (X < 3) {

    -
    - Demote all values to stack slots -
    -
    +

    + -reg2mem: Demote all values to stack slots +

    +

    This file demotes all registers to memory references. It is intented to be the inverse of -mem2reg. By converting to - load instructions, the only values live accross basic blocks are + load instructions, the only values live across basic blocks are alloca instructions and load instructions before phi 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 @@ -1657,10 +1629,10 @@ if (X < 3) {

    -
    - Scalar Replacement of Aggregates -
    -
    +

    + -scalarrepl: Scalar Replacement of Aggregates (DT) +

    +

    The well-known scalar replacement of aggregates transformation. This transform breaks up alloca instructions of aggregate type (structure @@ -1679,10 +1651,10 @@ if (X < 3) {

    -
    - Sparse Conditional Constant Propagation -
    -
    +

    + -sccp: Sparse Conditional Constant Propagation +

    +

    Sparse conditional constant propagation and merging, which can be summarized as: @@ -1702,10 +1674,10 @@ if (X < 3) {

    -
    - Simplify well-known library calls -
    -
    +

    + -simplify-libcalls: Simplify well-known library calls +

    +

    Applies a variety of small optimizations for calls to specific well-known function calls (e.g. runtime library functions). For example, a call @@ -1715,10 +1687,10 @@ if (X < 3) {

    -
    - Simplify the CFG -
    -
    +

    + -simplifycfg: Simplify the CFG +

    +

    Performs dead code elimination and basic block merging. Specifically:

    @@ -1734,12 +1706,45 @@ if (X < 3) {
    -
    - Strip all symbols from a module +

    + -sink: Code sinking +

    +
    +

    This pass moves instructions into successor blocks, when possible, so that + they aren't executed on paths where their results aren't needed. +

    -
    + + +

    + -sretpromotion: Promote sret arguments to multiple ret values +

    +
    +

    + This pass finds functions that return a struct (using a pointer to the struct + as the first argument of the function, marked with the 'sret' attribute) and + replaces them with a new function that simply returns each of the elements of + that struct (using multiple return values). +

    +

    - Performs code stripping. This transformation can delete: + This pass works under a number of conditions: +

    + +
      +
    • The returned struct must not contain other structs
      • +
    • The returned struct must only be used to load values from
      • +
    • The placeholder struct passed in is the result of an alloca
      • +
    +
    + + +

    + -strip: Strip all symbols from a module +

    +
    +

    + performs code stripping. this transformation can delete:

      @@ -1749,17 +1754,39 @@ if (X < 3) {

    - 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 strip utility would be used, such as reducing code size or making it harder to reverse engineer code.

    -
    - Remove unused function declarations +

    + -strip-dead-debug-info: Strip debug info for unused symbols +

    +
    +

    + performs code stripping. this transformation can delete: +

    + +
      +
    1. names for virtual registers
      2. +
    2. symbols for internal globals and functions
      3. +
    3. debug information
      4. +
    + +

    + 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. +

    -
    + + +

    + -strip-dead-prototypes: Strip Unused Function Prototypes +

    +

    This pass loops over all of the functions in the input module, looking for dead declarations and removes them. Dead declarations are declarations of @@ -1769,33 +1796,46 @@ if (X < 3) {

    -
    - Promote sret arguments -
    -
    -

    - This pass finds functions that return a struct (using a pointer to the struct - as the first argument of the function, marked with the 'sret' attribute) and - replaces them with a new function that simply returns each of the elements of - that struct (using multiple return values). -

    - +

    + -strip-debug-declare: Strip all llvm.dbg.declare intrinsics +

    +
    +

    This pass implements code stripping. Specifically, it can delete:

    +
      +
    • names for virtual registers
      • +
    • symbols for internal globals and functions
      • +
    • debug information
      • +

    - This pass works under a number of conditions: + 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.

    +
    + +

    + -strip-nondebug: Strip all symbols, except dbg symbols, from a module +

    +
    +

    This pass implements code stripping. Specifically, it can delete:

      -
    • The returned struct must not contain other structs
      • -
    • The returned struct must only be used to load values from
      • -
    • The placeholder struct passed in is the result of an alloca
      • +
    • names for virtual registers
      • +
    • symbols for internal globals and functions
      • +
    • debug information
    +

    + 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. +

    -
    - Tail Call Elimination -
    -
    +

    + -tailcallelim: Tail Call Elimination +

    +

    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 @@ -1824,10 +1864,10 @@ if (X < 3) {

    -
    - Tail Duplication -
    -
    +

    + -tailduplicate: Tail Duplication +

    +

    This pass performs a limited form of tail duplication, intended to simplify CFGs by removing some unconditional branches. This pass is necessary to @@ -1837,17 +1877,18 @@ if (X < 3) {

    +
    + -
    Utility Passes
    -
    +

    Utility Passes

    +

    This section describes the LLVM Utility Passes.

    -
    -
    - Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE) -
    -
    +

    + -deadarghaX0r: Dead Argument Hacking (BUGPOINT USE ONLY; DO NOT USE) +

    +

    Same as dead argument elimination, but deletes arguments to functions which are external. This is only for use by

    -
    - Extract Basic Blocks From Module (for bugpoint use) -
    -
    +

    + -extract-blocks: Extract Basic Blocks From Module (for bugpoint use) +

    +

    This pass is used by bugpoint to extract all blocks from the module into their own functions.

    -
    - Preliminary module verification +

    + -instnamer: Assign names to anonymous instructions +

    +
    +

    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. +

    -
    + + +

    + -preverify: Preliminary module verification +

    +

    Ensures that the module is in the form required by the Module Verifier pass. @@ -1881,10 +1934,10 @@ if (X < 3) {

    -
    - Module Verifier -
    -
    +

    + -verify: Module Verifier +

    +

    Verifies an LLVM IR code. This is useful to run after an optimization which is undergoing testing. Note that llvm-as verifies its input before @@ -1902,8 +1955,8 @@ if (X < 3) { integrals f.e.

  2. All of the constants in a switch statement are of the correct type.
  3. The code is in valid SSA form.
    4. -
  4. It should be illegal to put a label into any other type (like a - structure) or to return one. [except constant arrays!]
    5. +
  5. It is illegal to put a label into any other type (like a structure) or + to return one.
  6. Only phi nodes can be self referential: %x = add i32 %x, %x is invalid.
  7. PHI nodes must have an entry for each predecessor, with no extras.
    8. @@ -1932,26 +1985,70 @@ if (X < 3) {
    -
    - View CFG of function -
    -
    +

    + -view-cfg: View CFG of function +

    +

    Displays the control flow graph using the GraphViz tool.

    -
    - View CFG of function (with no function bodies) -
    -
    +

    + -view-cfg-only: View CFG of function (with no function bodies) +

    +

    Displays the control flow graph using the GraphViz tool, but omitting function bodies.

    + +

    + -view-dom: View dominance tree of function +

    +
    +

    + Displays the dominator tree using the GraphViz tool. +

    +
    + + +

    + -view-dom-only: View dominance tree of function (with no function bodies) +

    +
    +

    + Displays the dominator tree using the GraphViz tool, but omitting function + bodies. +

    +
    + + +

    + -view-postdom: View postdominance tree of function +

    +
    +

    + Displays the post dominator tree using the GraphViz tool. +

    +
    + + +

    + -view-postdom-only: View postdominance tree of function (with no function bodies) +

    +
    +

    + Displays the post dominator tree using the GraphViz tool, but omitting + function bodies. +

    +
    + +
    +
    @@ -1962,7 +2059,7 @@ if (X < 3) { src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"> Reid Spencer
    - LLVM Compiler Infrastructure
    + LLVM Compiler Infrastructure
    Last modified: $Date$