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InstCombine: Stop two transforms dueling

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InstCombineMulDivRem has:
// Canonicalize (X+C1)*CI -> X*CI+C1*CI.

InstCombineAddSub has:
// W*X + Y*Z --> W * (X+Z)  iff W == Y

These two transforms could fight with each other if C1*CI would not fold
away to something simpler than a ConstantExpr mul.

The InstCombineMulDivRem transform only acted on ConstantInts until
r199602 when it was changed to operate on all Constants in order to
let it fire on ConstantVectors.

To fix this, make this transform more careful by checking to see if we
actually folded away C1*CI.

This fixes PR20079.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211258 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-06-19 07:14:33 +00:00
parent 179bb4e0ee
commit 6c2e8874b0
2 changed files with 18 additions and 2 deletions
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lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+5 -2
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@@ -203,8 +203,11 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
Value *X;
Constant *C1;
if (match(Op0, m_OneUse(m_Add(m_Value(X), m_Constant(C1))))) {
Value *Add = Builder->CreateMul(X, Op1);
return BinaryOperator::CreateAdd(Add, Builder->CreateMul(C1, Op1));
Value *Mul = Builder->CreateMul(C1, Op1);
// Only go forward with the transform if C1*CI simplifies to a tidier
// constant.
if (!match(Mul, m_Mul(m_Value(), m_Value())))
return BinaryOperator::CreateAdd(Builder->CreateMul(X, Op1), Mul);
}
}
}