Generalize this optimization to work on equality comparisons between any two
integers that are constant except for a single bit (the same n-th bit in each).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90646 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index d12ad81..2b4b66b 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8585,25 +8585,36 @@
if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
uint32_t BitWidth = ITy->getBitWidth();
- if (BitWidth > 1) {
- Value *LHS = ICI->getOperand(0);
- Value *RHS = ICI->getOperand(1);
+ Value *LHS = ICI->getOperand(0);
+ Value *RHS = ICI->getOperand(1);
- APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
- APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
- APInt TypeMask(APInt::getHighBitsSet(BitWidth, BitWidth-1));
- ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS);
- ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS);
+ APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
+ APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
+ APInt TypeMask(APInt::getAllOnesValue(BitWidth));
+ ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS);
+ ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS);
- if (KnownZeroLHS.countLeadingOnes() == BitWidth-1 &&
- KnownZeroRHS.countLeadingOnes() == BitWidth-1) {
+ if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) {
+ APInt KnownBits = KnownZeroLHS | KnownOneLHS;
+ APInt UnknownBit = ~KnownBits;
+ if (UnknownBit.countPopulation() == 1) {
if (!DoXform) return ICI;
- Value *Xor = Builder->CreateXor(LHS, RHS);
+ Value *Result = Builder->CreateXor(LHS, RHS);
+
+ // Mask off any bits that are set and won't be shifted away.
+ if (KnownOneLHS.uge(UnknownBit))
+ Result = Builder->CreateAnd(Result,
+ ConstantInt::get(ITy, UnknownBit));
+
+ // Shift the bit we're testing down to the lsb.
+ Result = Builder->CreateLShr(
+ Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros()));
+
if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
- Xor = Builder->CreateXor(Xor, ConstantInt::get(ITy, 1));
- Xor->takeName(ICI);
- return ReplaceInstUsesWith(CI, Xor);
+ Result = Builder->CreateXor(Result, ConstantInt::get(ITy, 1));
+ Result->takeName(ICI);
+ return ReplaceInstUsesWith(CI, Result);
}
}
}