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Necessary changes to codegen cttz efficiently on PowerPC

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1. Teach LegalizeDAG how to better legalize CTTZ if the target doesn't have
   CTPOP, but does have CTLZ
2. Teach PPC32 how to do sub x, const -> add x, -const for valid consts
3. Teach PPC32 how to do and (xor a, -1) b -> andc b, a
4. Teach PPC32 that ISD::CTLZ -> PPC::CNTLZW


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21880 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nate Begeman
2005-05-11 23:43:56 +00:00
parent a65640edd0
commit d7c4a4a6c0
2 changed files with 41 additions and 9 deletions
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16
lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
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@@ -1156,15 +1156,25 @@ SDOperand SelectionDAGLegalize::LegalizeOp(SDOperand Op) {
break;
}
case ISD::CTTZ: {
// for now, we use: { return popcount(~x & (x - 1)); }
// but see also http://www.hackersdelight.org/HDcode/ntz.cc
// for now, we use: { return popcount(~x & (x - 1)); }
// unless the target has ctlz but not ctpop, in which case we use:
// { return 32 - nlz(~x & (x-1)); }
// see also http://www.hackersdelight.org/HDcode/ntz.cc
MVT::ValueType VT = Tmp1.getValueType();
Tmp2 = DAG.getConstant(~0ULL, VT);
Tmp3 = DAG.getNode(ISD::AND, VT,
DAG.getNode(ISD::XOR, VT, Tmp1, Tmp2),
DAG.getNode(ISD::SUB, VT, Tmp1,
DAG.getConstant(1, VT)));
Result = LegalizeOp(DAG.getNode(ISD::CTPOP, VT, Tmp3));
// If ISD::CTLZ is legal and CTPOP isn't, then do that instead
if (TLI.getOperationAction(ISD::CTPOP, VT) != TargetLowering::Legal &&
TLI.getOperationAction(ISD::CTLZ, VT) == TargetLowering::Legal) {
Result = LegalizeOp(DAG.getNode(ISD::SUB, VT,
DAG.getConstant(getSizeInBits(VT), VT),
DAG.getNode(ISD::CTLZ, VT, Tmp3)));
} else {
Result = LegalizeOp(DAG.getNode(ISD::CTPOP, VT, Tmp3));
}
break;
}
default: