[RISCV][GISEL] Legalize G_INSERT_SUBVECTOR

This code is heavily based on the SelectionDAG lowerINSERT_SUBVECTOR code.

Author: michaelmaitland

llvm/include/llvm/CodeGen/GlobalISel/GenericMachineInstrs.h

@@ -811,6 +811,18 @@ class GExtractSubvector : public GenericMachineInstr {
   }
 };
 
+/// Represents a insert subvector.
+class GInsertSubvector : public GenericMachineInstr {
+public:
+  Register getBigVec() const { return getOperand(1).getReg(); }
+  Register getSubVec() const { return getOperand(2).getReg(); }
+  uint64_t getIndexImm() const { return getOperand(3).getImm(); }
+
+  static bool classof(const MachineInstr *MI) {
+    return MI->getOpcode() == TargetOpcode::G_INSERT_SUBVECTOR;
+  }
+};
+
 /// Represents a freeze.
 class GFreeze : public GenericMachineInstr {
 public:

llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h

@@ -380,6 +380,8 @@ class LegalizerHelper {
                                      LLT CastTy);
   LegalizeResult bitcastExtractSubvector(MachineInstr &MI, unsigned TypeIdx,
                                          LLT CastTy);
+  LegalizeResult bitcastInsertSubvector(MachineInstr &MI, unsigned TypeIdx,
+                                        LLT CastTy);
 
   LegalizeResult lowerConstant(MachineInstr &MI);
   LegalizeResult lowerFConstant(MachineInstr &MI);

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -3725,6 +3725,77 @@ LegalizerHelper::bitcastExtractSubvector(MachineInstr &MI, unsigned TypeIdx,
   return Legalized;
 }
 
+/// This attempts to bitcast G_INSERT_SUBVECTOR to CastTy.
+///
+///  <vscale x 16 x i1> = G_INSERT_SUBVECTOR <vscale x 16 x i1>,
+///                                          <vscale x 8 x i1>,
+///                                          N
+///
+/// ===>
+///
+///  <vscale x 2 x i8> = G_BITCAST <vscale x 16 x i1>
+///  <vscale x 1 x i8> = G_BITCAST <vscale x 8 x i1>
+///  <vscale x 2 x i8> = G_INSERT_SUBVECTOR <vscale x 2 x i8>,
+///                                         <vscale x 1 x i8>, N / 8
+///  <vscale x 16 x i1> = G_BITCAST <vscale x 2 x i8>
+LegalizerHelper::LegalizeResult
+LegalizerHelper::bitcastInsertSubvector(MachineInstr &MI, unsigned TypeIdx,
+                                        LLT CastTy) {
+  auto ES = cast<GInsertSubvector>(&MI);
+
+  if (!CastTy.isVector())
+    return UnableToLegalize;
+
+  if (TypeIdx != 0)
+    return UnableToLegalize;
+
+  Register Dst = ES->getReg(0);
+  Register BigVec = ES->getBigVec();
+  Register SubVec = ES->getSubVec();
+  uint64_t Idx = ES->getIndexImm();
+
+  MachineRegisterInfo &MRI = *MIRBuilder.getMRI();
+
+  LLT DstTy = MRI.getType(Dst);
+  LLT BigVecTy = MRI.getType(BigVec);
+  LLT SubVecTy = MRI.getType(SubVec);
+
+  if (DstTy == CastTy)
+    return Legalized;
+
+  if (DstTy.getSizeInBits() != CastTy.getSizeInBits())
+    return UnableToLegalize;
+
+  ElementCount DstTyEC = DstTy.getElementCount();
+  ElementCount BigVecTyEC = BigVecTy.getElementCount();
+  ElementCount SubVecTyEC = SubVecTy.getElementCount();
+  auto DstTyMinElts = DstTyEC.getKnownMinValue();
+  auto BigVecTyMinElts = BigVecTyEC.getKnownMinValue();
+  auto SubVecTyMinElts = SubVecTyEC.getKnownMinValue();
+
+  unsigned CastEltSize = CastTy.getElementType().getSizeInBits();
+  unsigned DstEltSize = DstTy.getElementType().getSizeInBits();
+  if (CastEltSize < DstEltSize)
+    return UnableToLegalize;
+
+  auto AdjustAmt = CastEltSize / DstEltSize;
+  if (Idx % AdjustAmt != 0 || DstTyMinElts % AdjustAmt != 0 ||
+      BigVecTyMinElts % AdjustAmt != 0 || SubVecTyMinElts % AdjustAmt != 0)
+    return UnableToLegalize;
+
+  Idx /= AdjustAmt;
+  BigVecTy = LLT::vector(BigVecTyEC.divideCoefficientBy(AdjustAmt), AdjustAmt);
+  SubVecTy = LLT::vector(SubVecTyEC.divideCoefficientBy(AdjustAmt), AdjustAmt);
+  auto CastBigVec = MIRBuilder.buildBitcast(BigVecTy, BigVec);
+  auto CastSubVec = MIRBuilder.buildBitcast(SubVecTy, SubVec);
+  auto PromotedIS =
+      MIRBuilder.buildInsertSubvector(CastTy, CastBigVec, CastSubVec, Idx);
+  MIRBuilder.buildBitcast(Dst, PromotedIS);
+
+  ES->eraseFromParent();
+  return Legalized;
+}
+
 LegalizerHelper::LegalizeResult LegalizerHelper::lowerLoad(GAnyLoad &LoadMI) {
   // Lower to a memory-width G_LOAD and a G_SEXT/G_ZEXT/G_ANYEXT
   Register DstReg = LoadMI.getDstReg();
@@ -4033,6 +4104,8 @@ LegalizerHelper::bitcast(MachineInstr &MI, unsigned TypeIdx, LLT CastTy) {
     return bitcastConcatVector(MI, TypeIdx, CastTy);
   case TargetOpcode::G_EXTRACT_SUBVECTOR:
     return bitcastExtractSubvector(MI, TypeIdx, CastTy);
+  case TargetOpcode::G_INSERT_SUBVECTOR:
+    return bitcastInsertSubvector(MI, TypeIdx, CastTy);
   default:
     return UnableToLegalize;
   }

llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp

@@ -615,6 +615,13 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
           all(typeIsLegalIntOrFPVec(0, IntOrFPVecTys, ST),
               typeIsLegalIntOrFPVec(1, IntOrFPVecTys, ST))));
 
+
+  getActionDefinitionsBuilder(G_INSERT_SUBVECTOR)
+      .customIf(all(typeIsLegalBoolVec(0, BoolVecTys, ST),
+                    typeIsLegalBoolVec(1, BoolVecTys, ST)))
+      .customIf(all(typeIsLegalIntOrFPVec(0, IntOrFPVecTys, ST),
+                    typeIsLegalIntOrFPVec(1, IntOrFPVecTys, ST)));
+
   getLegacyLegalizerInfo().computeTables();
 }
 
@@ -833,10 +840,8 @@ static MachineInstrBuilder buildAllOnesMask(LLT VecTy, const SrcOp &VL,
 
 /// Gets the two common "VL" operands: an all-ones mask and the vector length.
 /// VecTy is a scalable vector type.
-static std::pair<MachineInstrBuilder, MachineInstrBuilder>
-buildDefaultVLOps(const DstOp &Dst, MachineIRBuilder &MIB,
-                  MachineRegisterInfo &MRI) {
-  LLT VecTy = Dst.getLLTTy(MRI);
+static std::pair<MachineInstrBuilder, Register>
+buildDefaultVLOps(LLT VecTy, MachineIRBuilder &MIB, MachineRegisterInfo &MRI) {
   assert(VecTy.isScalableVector() && "Expecting scalable container type");
   const RISCVSubtarget &STI = MIB.getMF().getSubtarget<RISCVSubtarget>();
   LLT XLenTy(STI.getXLenVT());
@@ -890,7 +895,7 @@ bool RISCVLegalizerInfo::legalizeSplatVector(MachineInstr &MI,
   // Handle case of s64 element vectors on rv32
   if (XLenTy.getSizeInBits() == 32 &&
       VecTy.getElementType().getSizeInBits() == 64) {
-    auto [_, VL] = buildDefaultVLOps(Dst, MIB, MRI);
+    auto [_, VL] = buildDefaultVLOps(MRI.getType(Dst), MIB, MRI);
     buildSplatSplitS64WithVL(Dst, MIB.buildUndef(VecTy), SplatVal, VL, MIB,
                              MRI);
     MI.eraseFromParent();
@@ -1025,6 +1030,142 @@ bool RISCVLegalizerInfo::legalizeExtractSubvector(MachineInstr &MI,
   return true;
 }
 
+bool RISCVLegalizerInfo::legalizeInsertSubvector(MachineInstr &MI,
+                                                 LegalizerHelper &Helper,
+                                                 MachineIRBuilder &MIB) const {
+  GInsertSubvector &IS = cast<GInsertSubvector>(MI);
+
+  MachineRegisterInfo &MRI = *MIB.getMRI();
+
+  Register Dst = IS.getReg(0);
+  Register BigVec = IS.getBigVec();
+  Register LitVec = IS.getSubVec();
+  uint64_t Idx = IS.getIndexImm();
+
+  LLT BigTy = MRI.getType(BigVec);
+  LLT LitTy = MRI.getType(LitVec);
+
+  if (Idx == 0 ||
+      MRI.getVRegDef(BigVec)->getOpcode() == TargetOpcode::G_IMPLICIT_DEF)
+    return true;
+
+  // We don't have the ability to slide mask vectors up indexed by their i1
+  // elements; the smallest we can do is i8. Often we are able to bitcast to
+  // equivalent i8 vectors. Otherwise, we can must zeroextend to equivalent i8
+  // vectors and truncate down after the insert.
+  if (LitTy.getElementType() == LLT::scalar(1)) {
+    auto BigTyMinElts = BigTy.getElementCount().getKnownMinValue();
+    auto LitTyMinElts = LitTy.getElementCount().getKnownMinValue();
+    if (BigTyMinElts >= 8 && LitTyMinElts >= 8)
+      return Helper.bitcast(
+          IS, 0,
+          LLT::vector(BigTy.getElementCount().divideCoefficientBy(8), 8));
+
+    // We can't slide this mask vector up indexed by its i1 elements.
+    // This poses a problem when we wish to insert a scalable vector which
+    // can't be re-expressed as a larger type. Just choose the slow path and
+    // extend to a larger type, then truncate back down.
+    BigTy = BigTy.changeElementType(LLT::scalar(8));
+    LitTy = LitTy.changeElementType(LLT::scalar(8));
+    auto BigZExt = MIB.buildZExt(BigTy, BigVec);
+    auto LitZExt = MIB.buildZExt(LitTy, LitVec);
+    auto Insert = MIB.buildInsertSubvector(BigTy, BigZExt, LitZExt, Idx);
+    auto SplatZero = MIB.buildSplatVector(
+        BigTy, MIB.buildConstant(BigTy.getElementType(), 0));
+    MIB.buildICmp(CmpInst::Predicate::ICMP_NE, Dst, Insert, SplatZero);
+    MI.eraseFromParent();
+    return true;
+  }
+
+  const RISCVRegisterInfo *TRI = STI.getRegisterInfo();
+  unsigned SubRegIdx, RemIdx;
+  std::tie(SubRegIdx, RemIdx) =
+      RISCVTargetLowering::decomposeSubvectorInsertExtractToSubRegs(
+          getMVTForLLT(BigTy), getMVTForLLT(LitTy), Idx, TRI);
+
+  TypeSize VecRegSize = TypeSize::getScalable(RISCV::RVVBitsPerBlock);
+  assert(isPowerOf2_64(
+      STI.expandVScale(LitTy.getSizeInBits()).getKnownMinValue()));
+  bool ExactlyVecRegSized =
+      STI.expandVScale(LitTy.getSizeInBits())
+          .isKnownMultipleOf(STI.expandVScale(VecRegSize));
+
+  // If the Idx has been completely eliminated and this subvector's size is a
+  // vector register or a multiple thereof, or the surrounding elements are
+  // undef, then this is a subvector insert which naturally aligns to a vector
+  // register. These can easily be handled using subregister manipulation.
+  if (RemIdx == 0 &&
+      (ExactlyVecRegSized ||
+       MRI.getVRegDef(BigVec)->getOpcode() == TargetOpcode::G_IMPLICIT_DEF))
+    return true;
+
+  // If the subvector is smaller than a vector register, then the insertion
+  // must preserve the undisturbed elements of the register. We do this by
+  // lowering to an EXTRACT_SUBVECTOR grabbing the nearest LMUL=1 vector type
+  // (which resolves to a subregister copy), performing a VSLIDEUP to place the
+  // subvector within the vector register, and an INSERT_SUBVECTOR of that
+  // LMUL=1 type back into the larger vector (resolving to another subregister
+  // operation). See below for how our VSLIDEUP works. We go via a LMUL=1 type
+  // to avoid allocating a large register group to hold our subvector.
+
+  // VSLIDEUP works by leaving elements 0<i<OFFSET undisturbed, elements
+  // OFFSET<=i<VL set to the "subvector" and vl<=i<VLMAX set to the tail policy
+  // (in our case undisturbed). This means we can set up a subvector insertion
+  // where OFFSET is the insertion offset, and the VL is the OFFSET plus the
+  // size of the subvector.
+  const LLT XLenTy(STI.getXLenVT());
+  LLT InterLitTy = BigTy;
+  Register AlignedExtract = BigVec;
+  unsigned AlignedIdx = Idx - RemIdx;
+  if (TypeSize::isKnownGT(BigTy.getSizeInBits(),
+                          getLMUL1Ty(BigTy).getSizeInBits())) {
+    InterLitTy = getLMUL1Ty(BigTy);
+    // Extract a subvector equal to the nearest full vector register type. This
+    // should resolve to a G_EXTRACT on a subreg.
+    AlignedExtract =
+        MIB.buildExtractSubvector(InterLitTy, BigVec, AlignedIdx).getReg(0);
+  }
+
+  auto Insert = MIB.buildInsertSubvector(InterLitTy, MIB.buildUndef(InterLitTy),
+                                         LitVec, 0);
+
+  auto [Mask, _] = buildDefaultVLOps(BigTy, MIB, MRI);
+  auto VL = MIB.buildVScale(XLenTy, LitTy.getElementCount().getKnownMinValue());
+
+  // Use tail agnostic policy if we're inserting over InterLitTy's tail.
+  ElementCount EndIndex =
+      ElementCount::getScalable(RemIdx) + LitTy.getElementCount();
+  uint64_t Policy = RISCVII::TAIL_UNDISTURBED_MASK_UNDISTURBED;
+  if (STI.expandVScale(EndIndex) ==
+      STI.expandVScale(InterLitTy.getElementCount()))
+    Policy = RISCVII::TAIL_AGNOSTIC;
+
+  // If we're inserting into the lowest elements, use a tail undisturbed
+  // vmv.v.v.
+  MachineInstrBuilder Inserted;
+  if (RemIdx == 0) {
+    Inserted = MIB.buildInstr(RISCV::G_VMV_V_V_VL, {InterLitTy},
+                              {AlignedExtract, Insert, VL});
+  } else {
+    auto SlideupAmt = MIB.buildVScale(XLenTy, RemIdx);
+    // Construct the vector length corresponding to RemIdx + length(LitTy).
+    VL = MIB.buildAdd(XLenTy, SlideupAmt, VL);
+    Inserted =
+        MIB.buildInstr(RISCV::G_VSLIDEUP_VL, {InterLitTy},
+                       {AlignedExtract, Insert, SlideupAmt, Mask, VL, Policy});
+  }
+
+  // If required, insert this subvector back into the correct vector register.
+  // This should resolve to an INSERT_SUBREG instruction.
+  if (TypeSize::isKnownGT(BigTy.getSizeInBits(), InterLitTy.getSizeInBits()))
+    MIB.buildInsertSubvector(Dst, BigVec, LitVec, AlignedIdx);
+  else
+    Inserted->getOperand(0).setReg(Dst);
+
+  MI.eraseFromParent();
+  return true;
+}
+
 bool RISCVLegalizerInfo::legalizeCustom(
     LegalizerHelper &Helper, MachineInstr &MI,
     LostDebugLocObserver &LocObserver) const {
@@ -1092,6 +1233,8 @@ bool RISCVLegalizerInfo::legalizeCustom(
     return legalizeSplatVector(MI, MIRBuilder);
   case TargetOpcode::G_EXTRACT_SUBVECTOR:
     return legalizeExtractSubvector(MI, MIRBuilder);
+  case TargetOpcode::G_INSERT_SUBVECTOR:
+    return legalizeInsertSubvector(MI, Helper, MIRBuilder);
   case TargetOpcode::G_LOAD:
   case TargetOpcode::G_STORE:
     return legalizeLoadStore(MI, Helper, MIRBuilder);

llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h

@@ -47,6 +47,8 @@ class RISCVLegalizerInfo : public LegalizerInfo {
   bool legalizeExt(MachineInstr &MI, MachineIRBuilder &MIRBuilder) const;
   bool legalizeSplatVector(MachineInstr &MI, MachineIRBuilder &MIB) const;
   bool legalizeExtractSubvector(MachineInstr &MI, MachineIRBuilder &MIB) const;
+  bool legalizeInsertSubvector(MachineInstr &MI, LegalizerHelper &Helper,
+                               MachineIRBuilder &MIB) const;
   bool legalizeLoadStore(MachineInstr &MI, LegalizerHelper &Helper,
                          MachineIRBuilder &MIB) const;
 };

llvm/lib/Target/RISCV/RISCVInstrGISel.td

@@ -67,3 +67,20 @@ def G_VSLIDEDOWN_VL : RISCVGenericInstruction {
 }
 def : GINodeEquiv<G_VSLIDEDOWN_VL, riscv_slidedown_vl>;
 
+// Pseudo equivalent to a RISCVISD::VMV_V_V_VL
+def G_VMV_V_V_VL : RISCVGenericInstruction {
+  let OutOperandList = (outs type0:$dst);
+  let InOperandList = (ins type0:$vec, type2:$vl);
+  let hasSideEffects = false;
+}
+def : GINodeEquiv<G_VMV_V_V_VL, riscv_vmv_v_v_vl>;
+
+// Pseudo equivalent to a RISCVISD::VSLIDEUP_VL
+def G_VSLIDEUP_VL : RISCVGenericInstruction {
+  let OutOperandList = (outs type0:$dst);
+  let InOperandList = (ins type0:$merge, type0:$vec, type1:$idx, type2:$mask,
+                       type3:$vl, type4:$policy);
+  let hasSideEffects = false;
+}
+def : GINodeEquiv<G_VSLIDEUP_VL, riscv_slideup_vl>;
+