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Add a small transform: transform -(X<<Y) to (-X<<Y) when the shift has a single

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use and X is free to negate.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94941 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman
2010-01-31 02:30:23 +00:00
parent 894c1af05f
commit 694488f477
2 changed files with 15 additions and 0 deletions
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7
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@@ -676,6 +676,13 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
return BinaryOperator::CreateSDiv(Op1I->getOperand(0),
ConstantExpr::getNeg(DivRHS));
// 0 - (C << X) -> (-C << X)
if (Op1I->getOpcode() == Instruction::Shl)
if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0))
if (CSI->isZero())
if (Value *ShlLHSNeg = dyn_castNegVal(Op1I->getOperand(0)))
return BinaryOperator::CreateShl(ShlLHSNeg, Op1I->getOperand(1));
// X - X*C --> X * (1-C)
ConstantInt *C2 = 0;
if (dyn_castFoldableMul(Op1I, C2) == Op0) {