From a4a812feddfe542c2cfe13641d2cf012058e1c2d Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Thu, 31 Jul 2014 04:49:29 +0000 Subject: [PATCH] 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. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214385 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/InstCombine/InstCombineAddSub.cpp | 12 +++++++++--- test/Transforms/InstCombine/sub.ll | 9 +++++++++ 2 files changed, 18 insertions(+), 3 deletions(-) diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp index e80d6a9ee39..ed0e1c90888 100644 --- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp +++ b/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; } diff --git a/test/Transforms/InstCombine/sub.ll b/test/Transforms/InstCombine/sub.ll index 67b7c4996b0..114aff7efb8 100644 --- a/test/Transforms/InstCombine/sub.ll +++ b/test/Transforms/InstCombine/sub.ll @@ -464,3 +464,12 @@ define i32 @test38(i32 %A) { ; CHECK-NEXT: [[SEXT:%.*]] = sext i1 [[ICMP]] to i32 ; CHECK-NEXT: ret i32 [[SEXT]] } + +define i32 @test39(i32 %A, i32 %x) { + %B = sub i32 0, %A + %C = sub nsw i32 %x, %B + ret i32 %C +; CHECK-LABEL: @test39( +; CHECK: %C = add i32 %x, %A +; CHECK: ret i32 %C +} -- 2.34.1