InstCombine: Restrict computeKnownBits() on all Values to OptLevel > 2
As part of r251146 InstCombine was extended to call computeKnownBits on
every value in the function to determine whether it happens to be
constant. This increases typical compiletime by 1-3% (5% in irgen+opt
time) in my measurements. On the other hand this case did not trigger
once in the whole llvm-testsuite.
This patch introduces the notion of ExpensiveCombines which are only
enabled for OptLevel > 2. I removed the check in InstructionSimplify as
that is called from various places where the OptLevel is not known but
given the rarity of the situation I think a check in InstCombine is
enough.
Differential Revision: http://reviews.llvm.org/D16835
llvm-svn: 263047
diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index c490e06..ae4d802 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -185,6 +185,12 @@
PM.add(createScopedNoAliasAAWrapperPass());
}
+void PassManagerBuilder::addInstructionCombiningPass(
+ legacy::PassManagerBase &PM) const {
+ bool ExpensiveCombines = OptLevel > 2;
+ PM.add(createInstructionCombiningPass(ExpensiveCombines));
+}
+
void PassManagerBuilder::populateFunctionPassManager(
legacy::FunctionPassManager &FPM) {
addExtensionsToPM(EP_EarlyAsPossible, FPM);
@@ -230,7 +236,8 @@
MPM.add(createJumpThreadingPass()); // Thread jumps.
MPM.add(createCorrelatedValuePropagationPass()); // Propagate conditionals
MPM.add(createCFGSimplificationPass()); // Merge & remove BBs
- MPM.add(createInstructionCombiningPass()); // Combine silly seq's
+ // Combine silly seq's
+ addInstructionCombiningPass(MPM);
addExtensionsToPM(EP_Peephole, MPM);
MPM.add(createTailCallEliminationPass()); // Eliminate tail calls
@@ -238,7 +245,7 @@
MPM.add(createReassociatePass()); // Reassociate expressions
if (PrepareForThinLTO) {
MPM.add(createAggressiveDCEPass()); // Delete dead instructions
- MPM.add(createInstructionCombiningPass()); // Combine silly seq's
+ addInstructionCombiningPass(MPM); // Combine silly seq's
return;
}
// Rotate Loop - disable header duplication at -Oz
@@ -246,7 +253,7 @@
MPM.add(createLICMPass()); // Hoist loop invariants
MPM.add(createLoopUnswitchPass(SizeLevel || OptLevel < 3));
MPM.add(createCFGSimplificationPass());
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
MPM.add(createIndVarSimplifyPass()); // Canonicalize indvars
MPM.add(createLoopIdiomPass()); // Recognize idioms like memset.
MPM.add(createLoopDeletionPass()); // Delete dead loops
@@ -273,7 +280,7 @@
// Run instcombine after redundancy elimination to exploit opportunities
// opened up by them.
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
addExtensionsToPM(EP_Peephole, MPM);
MPM.add(createJumpThreadingPass()); // Thread jumps
MPM.add(createCorrelatedValuePropagationPass());
@@ -290,7 +297,7 @@
if (BBVectorize) {
MPM.add(createBBVectorizePass());
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
addExtensionsToPM(EP_Peephole, MPM);
if (OptLevel > 1 && UseGVNAfterVectorization)
MPM.add(createGVNPass(DisableGVNLoadPRE)); // Remove redundancies
@@ -308,7 +315,8 @@
MPM.add(createAggressiveDCEPass()); // Delete dead instructions
MPM.add(createCFGSimplificationPass()); // Merge & remove BBs
- MPM.add(createInstructionCombiningPass()); // Clean up after everything.
+ // Clean up after everything.
+ addInstructionCombiningPass(MPM);
addExtensionsToPM(EP_Peephole, MPM);
}
@@ -359,7 +367,7 @@
MPM.add(createDeadArgEliminationPass()); // Dead argument elimination
- MPM.add(createInstructionCombiningPass()); // Clean up after IPCP & DAE
+ addInstructionCombiningPass(MPM); // Clean up after IPCP & DAE
addExtensionsToPM(EP_Peephole, MPM);
MPM.add(createCFGSimplificationPass()); // Clean up after IPCP & DAE
}
@@ -480,7 +488,7 @@
// on -O1 and no #pragma is found). Would be good to have these two passes
// as function calls, so that we can only pass them when the vectorizer
// changed the code.
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
if (OptLevel > 1 && ExtraVectorizerPasses) {
// At higher optimization levels, try to clean up any runtime overlap and
// alignment checks inserted by the vectorizer. We want to track correllated
@@ -490,11 +498,11 @@
// dead (or speculatable) control flows or more combining opportunities.
MPM.add(createEarlyCSEPass());
MPM.add(createCorrelatedValuePropagationPass());
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
MPM.add(createLICMPass());
MPM.add(createLoopUnswitchPass(SizeLevel || OptLevel < 3));
MPM.add(createCFGSimplificationPass());
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
}
if (RunSLPAfterLoopVectorization) {
@@ -507,7 +515,7 @@
if (BBVectorize) {
MPM.add(createBBVectorizePass());
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
addExtensionsToPM(EP_Peephole, MPM);
if (OptLevel > 1 && UseGVNAfterVectorization)
MPM.add(createGVNPass(DisableGVNLoadPRE)); // Remove redundancies
@@ -522,13 +530,13 @@
addExtensionsToPM(EP_Peephole, MPM);
MPM.add(createCFGSimplificationPass());
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
if (!DisableUnrollLoops) {
MPM.add(createLoopUnrollPass()); // Unroll small loops
// LoopUnroll may generate some redundency to cleanup.
- MPM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(MPM);
// Runtime unrolling will introduce runtime check in loop prologue. If the
// unrolled loop is a inner loop, then the prologue will be inside the
@@ -595,7 +603,7 @@
// simplification opportunities, and both can propagate functions through
// function pointers. When this happens, we often have to resolve varargs
// calls, etc, so let instcombine do this.
- PM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(PM);
addExtensionsToPM(EP_Peephole, PM);
// Inline small functions
@@ -617,7 +625,7 @@
PM.add(createArgumentPromotionPass());
// The IPO passes may leave cruft around. Clean up after them.
- PM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(PM);
addExtensionsToPM(EP_Peephole, PM);
PM.add(createJumpThreadingPass());
@@ -656,10 +664,10 @@
// Now that we've optimized loops (in particular loop induction variables),
// we may have exposed more scalar opportunities. Run parts of the scalar
// optimizer again at this point.
- PM.add(createInstructionCombiningPass()); // Initial cleanup
+ addInstructionCombiningPass(PM); // Initial cleanup
PM.add(createCFGSimplificationPass()); // if-convert
PM.add(createSCCPPass()); // Propagate exposed constants
- PM.add(createInstructionCombiningPass()); // Clean up again
+ addInstructionCombiningPass(PM); // Clean up again
PM.add(createBitTrackingDCEPass());
// More scalar chains could be vectorized due to more alias information
@@ -675,7 +683,7 @@
PM.add(createLoadCombinePass());
// Cleanup and simplify the code after the scalar optimizations.
- PM.add(createInstructionCombiningPass());
+ addInstructionCombiningPass(PM);
addExtensionsToPM(EP_Peephole, PM);
PM.add(createJumpThreadingPass());
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index c251683..1909cba 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -177,6 +177,8 @@
private:
// Mode in which we are running the combiner.
const bool MinimizeSize;
+ /// Enable combines that trigger rarely but are costly in compiletime.
+ const bool ExpensiveCombines;
AliasAnalysis *AA;
@@ -195,11 +197,12 @@
public:
InstCombiner(InstCombineWorklist &Worklist, BuilderTy *Builder,
- bool MinimizeSize, AliasAnalysis *AA,
+ bool MinimizeSize, bool ExpensiveCombines, AliasAnalysis *AA,
AssumptionCache *AC, TargetLibraryInfo *TLI,
DominatorTree *DT, const DataLayout &DL, LoopInfo *LI)
: Worklist(Worklist), Builder(Builder), MinimizeSize(MinimizeSize),
- AA(AA), AC(AC), TLI(TLI), DT(DT), DL(DL), LI(LI), MadeIRChange(false) {}
+ ExpensiveCombines(ExpensiveCombines), AA(AA), AC(AC), TLI(TLI), DT(DT),
+ DL(DL), LI(LI), MadeIRChange(false) {}
/// \brief Run the combiner over the entire worklist until it is empty.
///
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index af8d569..d728f1a 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -78,6 +78,10 @@
STATISTIC(NumFactor , "Number of factorizations");
STATISTIC(NumReassoc , "Number of reassociations");
+static cl::opt<bool>
+EnableExpensiveCombines("expensive-combines",
+ cl::desc("Enable expensive instruction combines"));
+
Value *InstCombiner::EmitGEPOffset(User *GEP) {
return llvm::EmitGEPOffset(Builder, DL, GEP);
}
@@ -2770,9 +2774,9 @@
}
}
- // In general, it is possible for computeKnownBits to determine all bits in a
- // value even when the operands are not all constants.
- if (!I->use_empty() && I->getType()->isIntegerTy()) {
+ // In general, it is possible for computeKnownBits to determine all bits in
+ // a value even when the operands are not all constants.
+ if (ExpensiveCombines && !I->use_empty() && I->getType()->isIntegerTy()) {
unsigned BitWidth = I->getType()->getScalarSizeInBits();
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
@@ -3043,8 +3047,10 @@
combineInstructionsOverFunction(Function &F, InstCombineWorklist &Worklist,
AliasAnalysis *AA, AssumptionCache &AC,
TargetLibraryInfo &TLI, DominatorTree &DT,
+ bool ExpensiveCombines = true,
LoopInfo *LI = nullptr) {
auto &DL = F.getParent()->getDataLayout();
+ ExpensiveCombines |= EnableExpensiveCombines;
/// Builder - This is an IRBuilder that automatically inserts new
/// instructions into the worklist when they are created.
@@ -3064,8 +3070,8 @@
bool Changed = prepareICWorklistFromFunction(F, DL, &TLI, Worklist);
- InstCombiner IC(Worklist, &Builder, F.optForMinSize(), AA, &AC, &TLI, &DT,
- DL, LI);
+ InstCombiner IC(Worklist, &Builder, F.optForMinSize(), ExpensiveCombines,
+ AA, &AC, &TLI, &DT, DL, LI);
Changed |= IC.run();
if (!Changed)
@@ -3084,7 +3090,8 @@
auto *LI = AM->getCachedResult<LoopAnalysis>(F);
// FIXME: The AliasAnalysis is not yet supported in the new pass manager
- if (!combineInstructionsOverFunction(F, Worklist, nullptr, AC, TLI, DT, LI))
+ if (!combineInstructionsOverFunction(F, Worklist, nullptr, AC, TLI, DT,
+ ExpensiveCombines, LI))
// No changes, all analyses are preserved.
return PreservedAnalyses::all();
@@ -3121,7 +3128,8 @@
auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
auto *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
- return combineInstructionsOverFunction(F, Worklist, AA, AC, TLI, DT, LI);
+ return combineInstructionsOverFunction(F, Worklist, AA, AC, TLI, DT,
+ ExpensiveCombines, LI);
}
char InstructionCombiningPass::ID = 0;
@@ -3144,6 +3152,6 @@
initializeInstructionCombiningPassPass(*unwrap(R));
}
-FunctionPass *llvm::createInstructionCombiningPass() {
- return new InstructionCombiningPass();
+FunctionPass *llvm::createInstructionCombiningPass(bool ExpensiveCombines) {
+ return new InstructionCombiningPass(ExpensiveCombines);
}