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[RISCV] Lower a shuffle which is nearly identity except one replicated element #135292

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Merged
merged 1 commit into from
Apr 11, 2025
Merged

[RISCV] Lower a shuffle which is nearly identity except one replicated element #135292

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44 changes: 44 additions & 0 deletions llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4726,6 +4726,47 @@ static SDValue getDeinterleaveShiftAndTrunc(const SDLoc &DL, MVT VT,
DAG.getVectorIdxConstant(0, DL));
}

/// Match a single source shuffle which is an identity except that some
/// particular element is repeated. This can be lowered as a masked
/// vrgather.vi/vx. Note that the two source form of this is handled
/// by the recursive splitting logic and doesn't need special handling.
static SDValue lowerVECTOR_SHUFFLEAsVRGatherVX(ShuffleVectorSDNode *SVN,
const RISCVSubtarget &Subtarget,
SelectionDAG &DAG) {

SDLoc DL(SVN);
MVT VT = SVN->getSimpleValueType(0);
SDValue V1 = SVN->getOperand(0);
assert(SVN->getOperand(1).isUndef());
ArrayRef<int> Mask = SVN->getMask();
const unsigned NumElts = VT.getVectorNumElements();
MVT XLenVT = Subtarget.getXLenVT();

std::optional<int> SplatIdx;
for (auto [I, M] : enumerate(Mask)) {
if (M == -1 || I == (unsigned)M)
continue;
if (SplatIdx && *SplatIdx != M)
return SDValue();
SplatIdx = M;
}

if (!SplatIdx)
return SDValue();

SmallVector<SDValue> MaskVals;
for (int MaskIndex : Mask) {
bool SelectMaskVal = MaskIndex == *SplatIdx;
MaskVals.push_back(DAG.getConstant(SelectMaskVal, DL, XLenVT));
}
assert(MaskVals.size() == NumElts && "Unexpected select-like shuffle");
MVT MaskVT = MVT::getVectorVT(MVT::i1, NumElts);
SDValue SelectMask = DAG.getBuildVector(MaskVT, DL, MaskVals);
SDValue Splat = DAG.getVectorShuffle(VT, DL, V1, DAG.getUNDEF(VT),
SmallVector<int>(NumElts, *SplatIdx));
return DAG.getNode(ISD::VSELECT, DL, VT, SelectMask, Splat, V1);
}

// Lower the following shuffle to vslidedown.
// a)
// t49: v8i8 = extract_subvector t13, Constant:i64<0>
Expand Down Expand Up @@ -5852,6 +5893,9 @@ static SDValue lowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG,
if (SDValue V = lowerVECTOR_SHUFFLEAsRotate(SVN, DAG, Subtarget))
return V;

if (SDValue V = lowerVECTOR_SHUFFLEAsVRGatherVX(SVN, Subtarget, DAG))
return V;

// Match a spread(4,8) which can be done via extend and shift. Spread(2)
// is fully covered in interleave(2) above, so it is ignored here.
if (VT.getScalarSizeInBits() < Subtarget.getELen()) {
Expand Down
33 changes: 16 additions & 17 deletions llvm/test/CodeGen/RISCV/rvv/fixed-vectors-shuffle-int.ll
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Expand Up @@ -1419,11 +1419,11 @@ define <8 x i32> @shuffle_v8i32_locally_repeating_neg(<8 x i32> %a) {
define <8 x i8> @identity_splat0(<8 x i8> %v) {
; CHECK-LABEL: identity_splat0:
; CHECK: # %bb.0:
; CHECK-NEXT: lui a0, %hi(.LCPI88_0)
; CHECK-NEXT: addi a0, a0, %lo(.LCPI88_0)
; CHECK-NEXT: vsetivli zero, 8, e8, mf2, ta, ma
; CHECK-NEXT: vle8.v v10, (a0)
; CHECK-NEXT: vrgather.vv v9, v8, v10
; CHECK-NEXT: li a0, 25
; CHECK-NEXT: vsetivli zero, 8, e8, mf2, ta, mu
; CHECK-NEXT: vmv.s.x v0, a0
; CHECK-NEXT: vmv1r.v v9, v8
; CHECK-NEXT: vrgather.vi v9, v8, 0, v0.t
; CHECK-NEXT: vmv1r.v v8, v9
; CHECK-NEXT: ret
%shuf = shufflevector <8 x i8> %v, <8 x i8> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 0, i32 0, i32 5, i32 6, i32 7>
Expand All @@ -1433,11 +1433,11 @@ define <8 x i8> @identity_splat0(<8 x i8> %v) {
define <8 x i8> @identity_splat2(<8 x i8> %v) {
; CHECK-LABEL: identity_splat2:
; CHECK: # %bb.0:
; CHECK-NEXT: lui a0, %hi(.LCPI89_0)
; CHECK-NEXT: addi a0, a0, %lo(.LCPI89_0)
; CHECK-NEXT: vsetivli zero, 8, e8, mf2, ta, ma
; CHECK-NEXT: vle8.v v10, (a0)
; CHECK-NEXT: vrgather.vv v9, v8, v10
; CHECK-NEXT: li a0, 28
; CHECK-NEXT: vsetivli zero, 8, e8, mf2, ta, mu
; CHECK-NEXT: vmv.s.x v0, a0
; CHECK-NEXT: vmv1r.v v9, v8
; CHECK-NEXT: vrgather.vi v9, v8, 2, v0.t
; CHECK-NEXT: vmv1r.v v8, v9
; CHECK-NEXT: ret
%shuf = shufflevector <8 x i8> %v, <8 x i8> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 2, i32 2, i32 5, i32 6, i32 7>
Expand All @@ -1448,14 +1448,13 @@ define <8 x i8> @identity_splat2(<8 x i8> %v) {
define <8 x i8> @vmerge_vxm(<8 x i8> %v, i8 %s) {
; CHECK-LABEL: vmerge_vxm:
; CHECK: # %bb.0:
; CHECK-NEXT: lui a1, %hi(.LCPI90_0)
; CHECK-NEXT: addi a1, a1, %lo(.LCPI90_0)
; CHECK-NEXT: vsetivli zero, 8, e8, mf2, ta, ma
; CHECK-NEXT: vle8.v v10, (a1)
; CHECK-NEXT: vsetvli zero, zero, e8, mf2, tu, ma
; CHECK-NEXT: li a1, 25
; CHECK-NEXT: vsetivli zero, 8, e8, m1, tu, ma
; CHECK-NEXT: vmv.s.x v8, a0
; CHECK-NEXT: vsetvli zero, zero, e8, mf2, ta, ma
; CHECK-NEXT: vrgather.vv v9, v8, v10
; CHECK-NEXT: vmv.s.x v0, a1
; CHECK-NEXT: vmv1r.v v9, v8
; CHECK-NEXT: vsetivli zero, 8, e8, mf2, ta, mu
; CHECK-NEXT: vrgather.vi v9, v8, 0, v0.t
; CHECK-NEXT: vmv1r.v v8, v9
; CHECK-NEXT: ret
%ins = insertelement <8 x i8> %v, i8 %s, i32 0
Expand Down