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[SystemZ] Extend memcmp support to all constant lengths

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This uses the infrastructure added for memcpy and memmove in r189331.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189458 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Richard Sandiford
2013-08-28 09:01:51 +00:00
parent ead2d5a4be
commit 47e7096094
4 changed files with 192 additions and 34 deletions
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35
lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
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@ -141,6 +141,28 @@ EmitTargetCodeForMemset(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
return SDValue();
}
// Use CLC to compare [Src1, Src1 + Size) with [Src2, Src2 + Size),
// deciding whether to use a loop or straight-line code.
static SDValue emitCLC(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
SDValue Src1, SDValue Src2, uint64_t Size) {
SDVTList VTs = DAG.getVTList(MVT::Other, MVT::Glue);
EVT PtrVT = Src1.getValueType();
// A two-CLC sequence is a clear win over a loop, not least because it
// needs only one branch. A three-CLC sequence needs the same number
// of branches as a loop (i.e. 2), but is shorter. That brings us to
// lengths greater than 768 bytes. It seems relatively likely that
// a difference will be found within the first 768 bytes, so we just
// optimize for the smallest number of branch instructions, in order
// to avoid polluting the prediction buffer too much. A loop only ever
// needs 2 branches, whereas a straight-line sequence would need 3 or more.
if (Size > 3 * 256)
return DAG.getNode(SystemZISD::CLC_LOOP, DL, VTs, Chain, Src1, Src2,
DAG.getConstant(Size, PtrVT),
DAG.getConstant(Size / 256, PtrVT));
return DAG.getNode(SystemZISD::CLC, DL, VTs, Chain, Src1, Src2,
DAG.getConstant(Size, PtrVT));
}
// Convert the current CC value into an integer that is 0 if CC == 0,
// less than zero if CC == 1 and greater than zero if CC >= 2.
// The sequence starts with IPM, which puts CC into bits 29 and 28
@ -159,17 +181,12 @@ EmitTargetCodeForMemcmp(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
SDValue Src1, SDValue Src2, SDValue Size,
MachinePointerInfo Op1PtrInfo,
MachinePointerInfo Op2PtrInfo) const {
EVT PtrVT = Src1.getValueType();
if (ConstantSDNode *CSize = dyn_cast<ConstantSDNode>(Size)) {
uint64_t Bytes = CSize->getZExtValue();
if (Bytes >= 1 && Bytes <= 0x100) {
// A single CLC.
SDVTList VTs = DAG.getVTList(MVT::Other, MVT::Glue);
Chain = DAG.getNode(SystemZISD::CLC, DL, VTs, Chain,
Src1, Src2, Size, DAG.getConstant(0, PtrVT));
SDValue Glue = Chain.getValue(1);
return std::make_pair(addIPMSequence(DL, Glue, DAG), Chain);
}
assert(Bytes > 0 && "Caller should have handled 0-size case");
Chain = emitCLC(DAG, DL, Chain, Src1, Src2, Bytes);
SDValue Glue = Chain.getValue(1);
return std::make_pair(addIPMSequence(DL, Glue, DAG), Chain);
}
return std::make_pair(SDValue(), SDValue());
}