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LoadStoreVectorizer: improvements: better pointer analysis

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If OpB has an ADD NSW/NUW, we can use that to prove that adding 1
to OpA won't wrap if OpA + 1 == OpB.

Patch by Fiona Glaser

llvm-svn: 274324
This commit is contained in:
Matt Arsenault 2016-07-01 02:16:24 +00:00
parent 672f531e85
commit 8fd475f7bc
1 changed files with 26 additions and 5 deletions
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31
lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
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@ -286,20 +286,41 @@ bool Vectorizer::isConsecutiveAccess(Value *A, Value *B) {
if (!isa<SExtInst>(OpA) && !isa<ZExtInst>(OpA))
return false;
bool Signed = isa<SExtInst>(OpA);
OpA = dyn_cast<Instruction>(OpA->getOperand(0));
OpB = dyn_cast<Instruction>(OpB->getOperand(0));
if (!OpA || !OpB || OpA->getType() != OpB->getType())
return false;
// Now we need to prove that adding 1 to OpA won't overflow.
bool Safe = false;
// First attempt: if OpB is an add with NSW/NUW, and OpB is 1 added to OpA,
// we're okay.
if (OpB->getOpcode() == Instruction::Add &&
isa<ConstantInt>(OpB->getOperand(1)) &&
cast<ConstantInt>(OpB->getOperand(1))->getSExtValue() > 0) {
if (Signed)
Safe = cast<BinaryOperator>(OpB)->hasNoSignedWrap();
else
Safe = cast<BinaryOperator>(OpB)->hasNoUnsignedWrap();
}
unsigned BitWidth = OpA->getType()->getScalarSizeInBits();
APInt KnownZero = APInt(BitWidth, 0);
APInt KnownOne = APInt(BitWidth, 0);
computeKnownBits(OpA, KnownZero, KnownOne, DL, 0, nullptr, OpA, &DT);
// Second attempt:
// If any bits are known to be zero other than the sign bit in OpA, we can
// add 1 to it while guaranteeing no overflow of any sort.
KnownZero &= ~APInt::getHighBitsSet(BitWidth, 1);
if (KnownZero == 0)
if (!Safe) {
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(OpA, KnownZero, KnownOne, DL, 0, nullptr, OpA, &DT);
KnownZero &= ~APInt::getHighBitsSet(BitWidth, 1);
if (KnownZero != 0)
Safe = true;
}
if (!Safe)
return false;
const SCEV *OffsetSCEVA = SE.getSCEV(OpA);