diff options
Diffstat (limited to 'llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp')
-rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp index 4b1705ca69c..20d8a2785b8 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -2057,15 +2057,15 @@ Instruction *InstCombiner::foldICmpShrConstant(ICmpInst &Cmp, (!IsAShr && C.shl(ShAmtVal).lshr(ShAmtVal) == C)) && "Expected icmp+shr simplify did not occur."); - // If the bits shifted out are known zero, compare the unshifted value: + // Check if the bits shifted out are known to be zero. If so, we can compare + // against the unshifted value: // (X & 4) >> 1 == 2 --> (X & 4) == 4. Constant *ShiftedCmpRHS = ConstantInt::get(Shr->getType(), C << ShAmtVal); - if (Shr->isExact()) - return new ICmpInst(Pred, X, ShiftedCmpRHS); - if (Shr->hasOneUse()) { - // Canonicalize the shift into an 'and': - // icmp eq/ne (shr X, ShAmt), C --> icmp eq/ne (and X, HiMask), (C << ShAmt) + if (Shr->isExact()) + return new ICmpInst(Pred, X, ShiftedCmpRHS); + + // Otherwise strength reduce the shift into an 'and'. APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal)); Constant *Mask = ConstantInt::get(Shr->getType(), Val); Value *And = Builder.CreateAnd(X, Mask, Shr->getName() + ".mask"); |