From a92687d6365f3bef67f23929c568262045f5b45b Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Thu, 31 Jul 2014 04:49:29 +0000 Subject: InstCombine: Correctly propagate NSW/NUW for x-(-A) -> x+A We can only propagate the nsw bits if both subtraction instructions are marked with the appropriate bit. N.B. We only propagate the nsw bit in InstCombine because the nuw case is already handled in InstSimplify. This fixes PR20189. llvm-svn: 214385 --- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) (limited to 'llvm/lib/Transforms') diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp index e80d6a9ee39..ed0e1c90888 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp @@ -1462,11 +1462,17 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) { if (Value *V = SimplifyUsingDistributiveLaws(I)) return ReplaceInstUsesWith(I, V); - // If this is a 'B = x-(-A)', change to B = x+A. This preserves NSW/NUW. + // If this is a 'B = x-(-A)', change to B = x+A. if (Value *V = dyn_castNegVal(Op1)) { BinaryOperator *Res = BinaryOperator::CreateAdd(Op0, V); - Res->setHasNoSignedWrap(I.hasNoSignedWrap()); - Res->setHasNoUnsignedWrap(I.hasNoUnsignedWrap()); + + if (const auto *BO = dyn_cast(Op1)) { + assert(BO->getOpcode() == Instruction::Sub && + "Expected a subtraction operator!"); + if (BO->hasNoSignedWrap() && I.hasNoSignedWrap()) + Res->setHasNoSignedWrap(true); + } + return Res; } -- cgit v1.2.3