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[InstCombine] simplify logic for swapMayExposeCSEOpportunities; NFCI 

llvm-svn: 324122
This commit is contained in:
Sanjay Patel 2018-02-02 19:08:12 +00:00
parent 78c9ac4dc5
commit 1ea8697cdf
1 changed files with 9 additions and 23 deletions
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32
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -3897,31 +3897,17 @@ static bool swapMayExposeCSEOpportunities(const Value *Op0, const Value *Op1) {
// FIXME: we may want to go through inttoptrs or bitcasts.
if (Op0->getType()->isPointerTy())
return false;
// Count all uses of both Op0 and Op1 in a subtract.
// Each time Op0 is the first operand, count -1: swapping is bad, the
// subtract has already the same layout as the compare.
// Each time Op0 is the second operand, count +1: swapping is good, the
// subtract has a different layout as the compare.
// At the end, if the benefit is greater than 0, Op0 should come second to
// expose more CSE opportunities.
int GlobalSwapBenefits = 0;
// If a subtract already has the same operands as a compare, swapping would be
// bad. If a subtract has the same operands as a compare but in reverse order,
// then swapping is good.
int GoodToSwap = 0;
for (const User *U : Op0->users()) {
const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(U);
if (!BinOp || BinOp->getOpcode() != Instruction::Sub)
continue;
// If Op0 is the first argument, this is not beneficial to swap the
// arguments.
int LocalSwapBenefits = -1;
unsigned Op1Idx = 1;
if (BinOp->getOperand(Op1Idx) == Op0) {
Op1Idx = 0;
LocalSwapBenefits = 1;
}
if (BinOp->getOperand(Op1Idx) != Op1)
continue;
GlobalSwapBenefits += LocalSwapBenefits;
if (match(U, m_Sub(m_Specific(Op1), m_Specific(Op0))))
GoodToSwap++;
else if (match(U, m_Sub(m_Specific(Op0), m_Specific(Op1))))
GoodToSwap--;
}
return GlobalSwapBenefits > 0;
return GoodToSwap > 0;
}
/// \brief Check that one use is in the same block as the definition and all