Transform -X/C to X/-C, implementing a README.txt entry.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78812 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 669ef2d..b875420 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -3077,6 +3077,14 @@
RHS->getValue().exactLogBase2());
return BinaryOperator::CreateAShr(Op0, ShAmt, I.getName());
}
+
+ // -X/C --> X/-C provided the negation doesn't overflow.
+ if (SubOperator *Sub = dyn_cast<SubOperator>(Op0))
+ if (isa<Constant>(Sub->getOperand(0)) &&
+ cast<Constant>(Sub->getOperand(0))->isNullValue() &&
+ Sub->hasNoSignedOverflow())
+ return BinaryOperator::CreateSDiv(Sub->getOperand(1),
+ ConstantExpr::getNeg(RHS));
}
// If the sign bits of both operands are zero (i.e. we can prove they are