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[TargetLowering] Improve expansion of FSHL/FSHR by non-zero amount

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Use a simpler code sequence when the shift amount is known not to be
zero modulo the bit width.

Nothing much uses this until D77152 changes the translation of fshl and
fshr intrinsics.

Differential Revision: https://reviews.llvm.org/D82540
This commit is contained in:
Jay Foad 2020-05-29 10:57:42 +01:00
parent 5fecaffff0
commit 4e57aaab54
1 changed files with 43 additions and 23 deletions
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66
lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -6117,6 +6117,14 @@ bool TargetLowering::expandMUL(SDNode *N, SDValue &Lo, SDValue &Hi, EVT HiLoVT,
return Ok;
}
// Check that (every element of) Z is undef or not an exact multiple of BW.
static bool isNonZeroModBitWidth(SDValue Z, unsigned BW) {
return ISD::matchUnaryPredicate(
Z,
[=](ConstantSDNode *C) { return !C || C->getAPIntValue().urem(BW) != 0; },
true);
}
bool TargetLowering::expandFunnelShift(SDNode *Node, SDValue &Result,
SelectionDAG &DAG) const {
EVT VT = Node->getValueType(0);
@ -6127,40 +6135,52 @@ bool TargetLowering::expandFunnelShift(SDNode *Node, SDValue &Result,
!isOperationLegalOrCustomOrPromote(ISD::OR, VT)))
return false;
// fshl: X << (Z % BW) | Y >> 1 >> (BW - 1 - (Z % BW))
// fshr: X << 1 << (BW - 1 - (Z % BW)) | Y >> (Z % BW)
SDValue X = Node->getOperand(0);
SDValue Y = Node->getOperand(1);
SDValue Z = Node->getOperand(2);
unsigned EltSizeInBits = VT.getScalarSizeInBits();
unsigned BW = VT.getScalarSizeInBits();
bool IsFSHL = Node->getOpcode() == ISD::FSHL;
SDLoc DL(SDValue(Node, 0));
EVT ShVT = Z.getValueType();
SDValue Mask = DAG.getConstant(EltSizeInBits - 1, DL, ShVT);
SDValue ShAmt, InvShAmt;
if (isPowerOf2_32(EltSizeInBits)) {
// Z % BW -> Z & (BW - 1)
ShAmt = DAG.getNode(ISD::AND, DL, ShVT, Z, Mask);
// (BW - 1) - (Z % BW) -> ~Z & (BW - 1)
InvShAmt = DAG.getNode(ISD::AND, DL, ShVT, DAG.getNOT(DL, Z, ShVT), Mask);
} else {
SDValue BitWidthC = DAG.getConstant(EltSizeInBits, DL, ShVT);
ShAmt = DAG.getNode(ISD::UREM, DL, ShVT, Z, BitWidthC);
InvShAmt = DAG.getNode(ISD::SUB, DL, ShVT, Mask, ShAmt);
}
SDValue One = DAG.getConstant(1, DL, ShVT);
SDValue ShX, ShY;
if (IsFSHL) {
ShX = DAG.getNode(ISD::SHL, DL, VT, X, ShAmt);
SDValue ShY1 = DAG.getNode(ISD::SRL, DL, VT, Y, One);
ShY = DAG.getNode(ISD::SRL, DL, VT, ShY1, InvShAmt);
SDValue ShAmt, InvShAmt;
if (isNonZeroModBitWidth(Z, BW)) {
// fshl: X << C | Y >> (BW - C)
// fshr: X << (BW - C) | Y >> C
// where C = Z % BW is not zero
SDValue BitWidthC = DAG.getConstant(BW, DL, ShVT);
ShAmt = DAG.getNode(ISD::UREM, DL, ShVT, Z, BitWidthC);
InvShAmt = DAG.getNode(ISD::SUB, DL, ShVT, BitWidthC, ShAmt);
ShX = DAG.getNode(ISD::SHL, DL, VT, X, IsFSHL ? ShAmt : InvShAmt);
ShY = DAG.getNode(ISD::SRL, DL, VT, Y, IsFSHL ? InvShAmt : ShAmt);
} else {
SDValue ShX1 = DAG.getNode(ISD::SHL, DL, VT, X, One);
ShX = DAG.getNode(ISD::SHL, DL, VT, ShX1, InvShAmt);
ShY = DAG.getNode(ISD::SRL, DL, VT, Y, ShAmt);
// fshl: X << (Z % BW) | Y >> 1 >> (BW - 1 - (Z % BW))
// fshr: X << 1 << (BW - 1 - (Z % BW)) | Y >> (Z % BW)
SDValue Mask = DAG.getConstant(BW - 1, DL, ShVT);
if (isPowerOf2_32(BW)) {
// Z % BW -> Z & (BW - 1)
ShAmt = DAG.getNode(ISD::AND, DL, ShVT, Z, Mask);
// (BW - 1) - (Z % BW) -> ~Z & (BW - 1)
InvShAmt = DAG.getNode(ISD::AND, DL, ShVT, DAG.getNOT(DL, Z, ShVT), Mask);
} else {
SDValue BitWidthC = DAG.getConstant(BW, DL, ShVT);
ShAmt = DAG.getNode(ISD::UREM, DL, ShVT, Z, BitWidthC);
InvShAmt = DAG.getNode(ISD::SUB, DL, ShVT, Mask, ShAmt);
}
SDValue One = DAG.getConstant(1, DL, ShVT);
if (IsFSHL) {
ShX = DAG.getNode(ISD::SHL, DL, VT, X, ShAmt);
SDValue ShY1 = DAG.getNode(ISD::SRL, DL, VT, Y, One);
ShY = DAG.getNode(ISD::SRL, DL, VT, ShY1, InvShAmt);
} else {
SDValue ShX1 = DAG.getNode(ISD::SHL, DL, VT, X, One);
ShX = DAG.getNode(ISD::SHL, DL, VT, ShX1, InvShAmt);
ShY = DAG.getNode(ISD::SRL, DL, VT, Y, ShAmt);
}
}
Result = DAG.getNode(ISD::OR, DL, VT, ShX, ShY);
return true;