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Transform -X/C to X/-C, implementing a README.txt entry.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78812 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-08-12 16:37:02 +00:00
parent fa94b948d9
commit 9ca9daad21
3 changed files with 28 additions and 10 deletions
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8
lib/Transforms/Scalar/InstructionCombining.cpp
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@@ -3077,6 +3077,14 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
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