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/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);
}