diff options
Diffstat (limited to 'contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp')
-rw-r--r-- | contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp index 535a7736454c..4a459ec6c550 100644 --- a/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp +++ b/contrib/llvm-project/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp @@ -1966,12 +1966,14 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) { return BinaryOperator::CreateAdd(X, ConstantExpr::getSub(C, C2)); } - // If there's no chance any bit will need to borrow from an adjacent bit: - // sub C, X --> xor X, C const APInt *Op0C; - if (match(Op0, m_APInt(Op0C)) && - (~computeKnownBits(Op1, 0, &I).Zero).isSubsetOf(*Op0C)) - return BinaryOperator::CreateXor(Op1, Op0); + if (match(Op0, m_APInt(Op0C)) && Op0C->isMask()) { + // Turn this into a xor if LHS is 2^n-1 and the remaining bits are known + // zero. + KnownBits RHSKnown = computeKnownBits(Op1, 0, &I); + if ((*Op0C | RHSKnown.Zero).isAllOnes()) + return BinaryOperator::CreateXor(Op1, Op0); + } { Value *Y; |