Reduce x - y to -y when we know the 'x' part will get masked off anyways.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53271 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index f8ad98c..675f7ec 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -3461,6 +3461,17 @@
// ((A ^ N) - B) & AndRHS -> (A - B) & AndRHS iff N&AndRHS == 0
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)) {
+ ConstantInt *A = dyn_cast<ConstantInt>(Op0LHS);
+ if (!A || !A->isZero()) {
+ Instruction *NewNeg = BinaryOperator::CreateNeg(Op0RHS);
+ InsertNewInstBefore(NewNeg, I);
+ return BinaryOperator::CreateAnd(NewNeg, AndRHS);
+ }
+ }
+
break;
}
@@ -3780,7 +3791,7 @@
}
}
}
-
+
return Changed ? &I : 0;
}