diff options
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp index 0d56ce5ebe8..ac94cdb93b0 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -1074,18 +1074,22 @@ Instruction *InstCombiner::FoldICmpCstShrCst(ICmpInst &I, Value *Op, Value *A, if (AP1 == AP2) return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType())); - // Get the distance between the highest bit that's set. int Shift; - // Both the constants are negative, take their positive to calculate log. if (IsAShr && AP1.isNegative()) - // Get the ones' complement of AP2 and AP1 when computing the distance. - Shift = (~AP2).logBase2() - (~AP1).logBase2(); + Shift = AP1.countLeadingOnes() - AP2.countLeadingOnes(); else - Shift = AP2.logBase2() - AP1.logBase2(); + Shift = AP1.countLeadingZeros() - AP2.countLeadingZeros(); if (Shift > 0) { - if (IsAShr ? AP1 == AP2.ashr(Shift) : AP1 == AP2.lshr(Shift)) + if (IsAShr && AP1 == AP2.ashr(Shift)) { + // There are multiple solutions if we are comparing against -1 and the LHS + // of the ashr is not a power of two.. + if (AP1.isAllOnesValue() && !AP2.isPowerOf2()) + return getICmp(I.ICMP_UGE, A, ConstantInt::get(A->getType(), Shift)); return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift)); + } else if (AP1 == AP2.lshr(Shift)) { + return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift)); + } } // Shifting const2 will never be equal to const1. return getConstant(false); |
