From 5dcc41f5b3daf6ef7097f169767291ff9cd0dd0b Mon Sep 17 00:00:00 2001 From: Nick Lewycky Date: Thu, 10 Jul 2008 05:51:40 +0000 Subject: [PATCH] Fix overzealous optimization. Thanks to Duncan Sands for pointing out my error! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53393 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/InstructionCombining.cpp | 13 +++++++++---- .../InstCombine/2008-07-09-SubAndError.ll | 9 +++++++++ 2 files changed, 18 insertions(+), 4 deletions(-) create mode 100644 test/Transforms/InstCombine/2008-07-09-SubAndError.ll diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index c573f7f5312..e0e3f49be18 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -3462,16 +3462,21 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) { if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS, true, I)) return BinaryOperator::CreateAnd(V, AndRHS); - // (A - N) & AndRHS -> -N & AndRHS where A & AndRHS == 0 - if (Op0I->hasOneUse() && MaskedValueIsZero(Op0LHS, AndRHSMask)) { + // (A - N) & AndRHS -> -N & AndRHS iff A&AndRHS==0 and AndRHS + // has 1's for all bits that the subtraction with A might affect. + if (Op0I->hasOneUse()) { + uint32_t BitWidth = AndRHSMask.getBitWidth(); + uint32_t Zeros = AndRHSMask.countLeadingZeros(); + APInt Mask = APInt::getLowBitsSet(BitWidth, BitWidth - Zeros); + ConstantInt *A = dyn_cast(Op0LHS); - if (!A || !A->isZero()) { + if (!(A && A->isZero()) && // avoid infinite recursion. + MaskedValueIsZero(Op0LHS, Mask)) { Instruction *NewNeg = BinaryOperator::CreateNeg(Op0RHS); InsertNewInstBefore(NewNeg, I); return BinaryOperator::CreateAnd(NewNeg, AndRHS); } } - break; case Instruction::Shl: diff --git a/test/Transforms/InstCombine/2008-07-09-SubAndError.ll b/test/Transforms/InstCombine/2008-07-09-SubAndError.ll new file mode 100644 index 00000000000..c5b93586ba3 --- /dev/null +++ b/test/Transforms/InstCombine/2008-07-09-SubAndError.ll @@ -0,0 +1,9 @@ +; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep {sub i32 0} +; PR2330 + +define i32 @foo(i32 %a) nounwind { +entry: + %A = sub i32 5, %a + %B = and i32 %A, 2 + ret i32 %B +}