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Fix overzealous optimization. Thanks to Duncan Sands for pointing out my error! 

llvm-svn: 53393
This commit is contained in:
Nick Lewycky 2008-07-10 05:51:40 +00:00
parent cfba0fade8
commit 6193a564ab
2 changed files with 18 additions and 4 deletions
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13
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -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<ConstantInt>(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:

9
llvm/test/Transforms/InstCombine/2008-07-09-SubAndError.ll Normal file
View File

@ -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
}