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When we're doing a compare of load-AND-constant to 0

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(e.g. a bitfield test) narrow the load as much as possible.
The has the potential to avoid unnecessary partial-word
load-after-store conflicts, which cause stalls on several targets.
Also a size win on x86 (testb vs testl).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@58825 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen 2008-11-07 01:28:02 +00:00
parent b7c6ebcb47
commit 89217a6f18
1 changed files with 46 additions and 0 deletions
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46
lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -1352,6 +1352,52 @@ TargetLowering::SimplifySetCC(MVT VT, SDValue N0, SDValue N1,
Zero, Cond);
}
}
// If the LHS is '(and load, const)', the RHS is 0,
// the test is for equality or unsigned, and all 1 bits of the const are
// in the same partial word, see if we can shorten the load.
if (DCI.isBeforeLegalize() &&
N0.getOpcode() == ISD::AND && C1 == 0 &&
isa<LoadSDNode>(N0.getOperand(0)) &&
N0.getOperand(0).getNode()->hasOneUse() &&
isa<ConstantSDNode>(N0.getOperand(1))) {
LoadSDNode *Lod = cast<LoadSDNode>(N0.getOperand(0));
uint64_t Mask = cast<ConstantSDNode>(N0.getOperand(1))->getZExtValue();
unsigned bestWidth = 0, bestOffset = 0;
if (!Lod->isVolatile()) {
unsigned origWidth = N0.getValueType().getSizeInBits();
for (unsigned width = origWidth / 2; width>=8; width /= 2) {
uint64_t newMask = (1ULL << width) - 1;
for (unsigned offset=0; offset<origWidth/width; offset++) {
if ((newMask & Mask)==Mask) {
bestOffset = (uint64_t)offset * (width/8);
bestWidth = width;
break;
}
newMask = newMask << width;
}
}
}
if (bestWidth) {
MVT newVT = MVT::getIntegerVT(bestWidth);
if (newVT.isRound()) {
uint64_t bestMask = Mask >> (bestOffset * 8);
MVT PtrType = Lod->getOperand(1).getValueType();
SDValue Ptr = Lod->getBasePtr();
if (bestOffset != 0)
Ptr = DAG.getNode(ISD::ADD, PtrType, Lod->getBasePtr(),
DAG.getConstant(bestOffset, PtrType));
unsigned NewAlign = MinAlign(Lod->getAlignment(), bestOffset);
SDValue NewLoad = DAG.getLoad(newVT, Lod->getChain(), Ptr,
Lod->getSrcValue(),
Lod->getSrcValueOffset() + bestOffset,
false, NewAlign);
return DAG.getSetCC(VT, DAG.getNode(ISD::AND, newVT, NewLoad,
DAG.getConstant(bestMask, newVT)),
DAG.getConstant(0LL, newVT), Cond);
}
}
}
// If the LHS is a ZERO_EXTEND, perform the comparison on the input.
if (N0.getOpcode() == ISD::ZERO_EXTEND) {