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if two gep comparisons only differ by one index, compare that index directly. 

This allows us to better optimize begin() -> end() comparisons in common cases.

llvm-svn: 19542
This commit is contained in:
Chris Lattner 2005-01-14 00:20:05 +00:00
parent d35d210ea0
commit 4fa89827e2
1 changed files with 28 additions and 0 deletions
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28
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -2219,6 +2219,8 @@ Instruction *InstCombiner::FoldGEPSetCC(User *GEPLHS, Value *RHS,
if (AllZeros)
return FoldGEPSetCC(GEPRHS, GEPLHS->getOperand(0),
SetCondInst::getSwappedCondition(Cond), I);
// If the other GEP has all zero indices, recurse.
AllZeros = true;
for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i)
if (!isa<Constant>(GEPRHS->getOperand(i)) ||
@ -2229,6 +2231,32 @@ Instruction *InstCombiner::FoldGEPSetCC(User *GEPLHS, Value *RHS,
if (AllZeros)
return FoldGEPSetCC(GEPLHS, GEPRHS->getOperand(0), Cond, I);
if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands()) {
// If the GEPs only differ by one index, compare it.
unsigned NumDifferences = 0; // Keep track of # differences.
unsigned DiffOperand = 0; // The operand that differs.
for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i)
if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) {
if (GEPLHS->getOperand(i)->getType() !=
GEPRHS->getOperand(i)->getType()) {
// Irreconsilable differences.
NumDifferences = 2;
break;
} else {
if (NumDifferences++) break;
DiffOperand = i;
}
}
if (NumDifferences == 0) // SAME GEP?
return ReplaceInstUsesWith(I, // No comparison is needed here.
ConstantBool::get(Cond == Instruction::SetEQ));
else if (NumDifferences == 1) {
return new SetCondInst(Cond, GEPLHS->getOperand(DiffOperand),
GEPRHS->getOperand(DiffOperand));
}
}
// Only lower this if the setcc is the only user of the GEP or if we expect
// the result to fold to a constant!
if ((isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&