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
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index c573f7f..e0e3f49 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -3462,16 +3462,21 @@
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: