[llvm] [RISCV][GISEL] Legalize G_EXTRACT_SUBVECTOR (PR #109426)

Michael Maitland via llvm-commits llvm-commits at lists.llvm.org
Fri Sep 20 06:56:02 PDT 2024


https://github.com/michaelmaitland created https://github.com/llvm/llvm-project/pull/109426

This is heavily based on the SelectionDAG lowerEXTRACT_SUBVECTOR code.

>From 4771bee80792ae9b5e5d97da598d71a48237ecf8 Mon Sep 17 00:00:00 2001
From: Michael Maitland <michaeltmaitland at gmail.com>
Date: Mon, 16 Sep 2024 11:07:20 -0700
Subject: [PATCH] [RISCV][GISEL] Legalize G_EXTRACT_SUBVECTOR

---
 .../CodeGen/GlobalISel/GenericMachineInstrs.h |  11 +
 .../Target/RISCV/GISel/RISCVLegalizerInfo.cpp | 133 +++++++
 .../Target/RISCV/GISel/RISCVLegalizerInfo.h   |   1 +
 llvm/lib/Target/RISCV/RISCVInstrGISel.td      |  10 +
 .../rvv/legalize-extract-subvector.mir        | 339 ++++++++++++++++++
 5 files changed, 494 insertions(+)
 create mode 100644 llvm/test/CodeGen/RISCV/GlobalISel/legalizer/rvv/legalize-extract-subvector.mir

diff --git a/llvm/include/llvm/CodeGen/GlobalISel/GenericMachineInstrs.h b/llvm/include/llvm/CodeGen/GlobalISel/GenericMachineInstrs.h
index 132b7ec9aeef7c..d9f3f4ab3935d3 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/GenericMachineInstrs.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/GenericMachineInstrs.h
@@ -800,6 +800,17 @@ class GInsertVectorElement : public GenericMachineInstr {
   }
 };
 
+/// Represents an extract subvector.
+class GExtractSubvector : public GenericMachineInstr {
+public:
+  Register getSrcVec() const { return getOperand(1).getReg(); }
+  uint64_t getIndexImm() const { return getOperand(2).getImm(); }
+
+  static bool classof(const MachineInstr *MI) {
+    return MI->getOpcode() == TargetOpcode::G_EXTRACT_SUBVECTOR;
+  }
+};
+
 /// Represents a freeze.
 class GFreeze : public GenericMachineInstr {
 public:
diff --git a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
index 055193bcc2c8db..db53bc409392bd 100644
--- a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
+++ b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
@@ -597,6 +597,10 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
 
   SplatActions.clampScalar(1, sXLen, sXLen);
 
+  getActionDefinitionsBuilder(G_EXTRACT_SUBVECTOR)
+      .customIf(typeIsLegalBoolVec(0, BoolVecTys, ST))
+      .customIf(typeIsLegalIntOrFPVec(0, IntOrFPVecTys, ST));
+
   getLegacyLegalizerInfo().computeTables();
 }
 
@@ -931,6 +935,133 @@ bool RISCVLegalizerInfo::legalizeSplatVector(MachineInstr &MI,
   return true;
 }
 
+static LLT getLMUL1Ty(LLT VecTy) {
+  assert(VecTy.getElementType().getSizeInBits() <= 64 &&
+         "Unexpected vector LLT");
+  return LLT::scalable_vector(RISCV::RVVBitsPerBlock /
+                                  VecTy.getElementType().getSizeInBits(),
+                              VecTy.getElementType());
+}
+
+bool RISCVLegalizerInfo::legalizeExtractSubvector(MachineInstr &MI,
+                                                  MachineIRBuilder &MIB) const {
+  GExtractSubvector &ES = cast<GExtractSubvector>(MI);
+
+  MachineRegisterInfo &MRI = *MIB.getMRI();
+
+  Register Dst = ES.getReg(0);
+  Register Src = ES.getSrcVec();
+  uint64_t Idx = ES.getIndexImm();
+
+  // Only support vectors using custom legalization. We know the DstTy is a
+  // vector since we used that to decide whether to custom legalize or not.
+  LLT BigTy = MRI.getType(Src);
+  if (BigTy.isScalar())
+    return false;
+
+  LLT LitTy = MRI.getType(Dst);
+  Register Vec = Src;
+
+  // We don't have the ability to slide mask vectors down indexed by their i1
+  // elements; the smallest we can do is i8. Often we are able to bitcast to
+  // equivalent i8 vectors.
+  if (LitTy.getElementType() == LLT::scalar(1) && Idx != 0) {
+    auto BigTyMinElts = BigTy.getElementCount().getKnownMinValue();
+    auto LitTyMinElts = LitTy.getElementCount().getKnownMinValue();
+    if (BigTyMinElts >= 8 && LitTyMinElts >= 8) {
+      assert(Idx % 8 == 0 && "Invalid index");
+      assert(BigTyMinElts % 8 == 0 && LitTyMinElts % 8 == 0 &&
+             "Unexpected mask vector lowering");
+      Idx /= 8;
+      BigTy = LLT::vector(BigTy.getElementCount().divideCoefficientBy(8), 8);
+      LitTy = LLT::vector(LitTy.getElementCount().divideCoefficientBy(8), 8);
+      Vec = MIB.buildBitcast(BigTy, Vec).getReg(0);
+    } else {
+      // 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.
+      LLT ExtBigTy = BigTy.changeElementType(LLT::scalar(8));
+      LLT ExtLitTy = LitTy.changeElementType(LLT::scalar(8));
+      auto BigZExt = MIB.buildZExt(ExtBigTy, Vec);
+      auto ExtractZExt = MIB.buildExtractSubvector(ExtLitTy, BigZExt, Idx);
+      auto SplatZero = MIB.buildSplatVector(
+          ExtLitTy, MIB.buildConstant(ExtLitTy.getElementType(), 0));
+      MIB.buildICmp(CmpInst::Predicate::ICMP_NE, Dst, ExtractZExt, SplatZero);
+      MI.eraseFromParent();
+      return true;
+    }
+  }
+
+  // With an index of 0 this is a cast-like subvector, which can be performed
+  // with subregister operations.
+  if (Idx == 0)
+    return true;
+
+  // extract_subvector scales the index by vscale if the subvector is scalable,
+  // and decomposeSubvectorInsertExtractToSubRegs takes this into account.
+  const RISCVRegisterInfo *TRI = STI.getRegisterInfo();
+  MVT LitTyMVT = getMVTForLLT(LitTy);
+  unsigned SubRegIdx;
+  ElementCount RemIdx;
+  auto Decompose =
+      RISCVTargetLowering::decomposeSubvectorInsertExtractToSubRegs(
+          getMVTForLLT(BigTy), LitTyMVT, Idx, TRI);
+  SubRegIdx = Decompose.first;
+  RemIdx = ElementCount::getScalable(Decompose.second);
+
+  // If the Idx has been completely eliminated then this is a subvector extract
+  // which naturally aligns to a vector register. These can easily be handled
+  // using subregister manipulation.
+  // TODO: add tests
+  if (RemIdx.isZero())
+    return true;
+
+  // Else LitTy is M1 or smaller and may need to be slid down: if LitTy
+  // was > M1 then the index would need to be a multiple of VLMAX, and so would
+  // divide exactly.
+  assert(
+      RISCVVType::decodeVLMUL(RISCVTargetLowering::getLMUL(LitTyMVT)).second ||
+      RISCVTargetLowering::getLMUL(LitTyMVT) == RISCVII::VLMUL::LMUL_1);
+
+  // If the vector type is an LMUL-group type, extract a subvector equal to the
+  // nearest full vector register type.
+  LLT InterLitTy = BigTy;
+  if (TypeSize::isKnownGT(BigTy.getSizeInBits(),
+                          getLMUL1Ty(BigTy).getSizeInBits())) {
+    // If BigTy has an LMUL > 1, then LitTy should have a smaller LMUL, and
+    // we should have successfully decomposed the extract into a subregister.
+    assert(SubRegIdx != RISCV::NoSubRegister);
+    InterLitTy = getLMUL1Ty(BigTy);
+    // SDAG builds a TargetExtractSubreg. A Copy with SubReg specified on the
+    // source Register is the  equivalent.
+    Vec = MIB.buildInstr(TargetOpcode::COPY, {InterLitTy}, {})
+              .addReg(Vec, 0, SubRegIdx)
+              .getReg(0);
+  }
+
+  // Slide this vector register down by the desired number of elements in order
+  // to place the desired subvector starting at element 0.
+  const LLT XLenTy(STI.getXLenVT());
+  auto SlidedownAmt = MIB.buildVScale(XLenTy, RemIdx.getKnownMinValue());
+  auto [Mask, VL] = buildDefaultVLOps(LitTy, MIB, MRI);
+  uint64_t Policy = RISCVII::TAIL_AGNOSTIC | RISCVII::MASK_AGNOSTIC;
+  auto Slidedown = MIB.buildInstr(
+      RISCV::G_VSLIDEDOWN_VL, {InterLitTy},
+      {MIB.buildUndef(InterLitTy), Vec, SlidedownAmt, Mask, VL, Policy});
+
+  // Now the vector is in the right position, extract our final subvector. This
+  // should resolve to a COPY.
+  auto Extract = MIB.buildExtractSubvector(LitTy, Slidedown, 0);
+
+  // We might have bitcast from a mask type: cast back to the original type if
+  // required.
+  MIB.buildBitcast(Dst, Extract);
+
+  MI.eraseFromParent();
+  return true;
+}
+
 bool RISCVLegalizerInfo::legalizeCustom(
     LegalizerHelper &Helper, MachineInstr &MI,
     LostDebugLocObserver &LocObserver) const {
@@ -1001,6 +1132,8 @@ bool RISCVLegalizerInfo::legalizeCustom(
     return legalizeExt(MI, MIRBuilder);
   case TargetOpcode::G_SPLAT_VECTOR:
     return legalizeSplatVector(MI, MIRBuilder);
+  case TargetOpcode::G_EXTRACT_SUBVECTOR:
+    return legalizeExtractSubvector(MI, MIRBuilder);
   case TargetOpcode::G_LOAD:
   case TargetOpcode::G_STORE:
     return legalizeLoadStore(MI, Helper, MIRBuilder);
diff --git a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
index 2fc28615e7630d..d2afb175ae42bb 100644
--- a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
+++ b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h
@@ -46,6 +46,7 @@ class RISCVLegalizerInfo : public LegalizerInfo {
   bool legalizeVScale(MachineInstr &MI, MachineIRBuilder &MIB) const;
   bool legalizeExt(MachineInstr &MI, MachineIRBuilder &MIRBuilder) const;
   bool legalizeSplatVector(MachineInstr &MI, MachineIRBuilder &MIB) const;
+  bool legalizeExtractSubvector(MachineInstr &MI, MachineIRBuilder &MIB) const;
   bool legalizeLoadStore(MachineInstr &MI, LegalizerHelper &Helper,
                          MachineIRBuilder &MIB) const;
 };
diff --git a/llvm/lib/Target/RISCV/RISCVInstrGISel.td b/llvm/lib/Target/RISCV/RISCVInstrGISel.td
index ba40662c49c1df..b8641418aff747 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrGISel.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrGISel.td
@@ -57,3 +57,13 @@ def G_SPLAT_VECTOR_SPLIT_I64_VL : RISCVGenericInstruction {
   let InOperandList = (ins type0:$passthru, type1:$hi, type1:$lo, type2:$vl);
   let hasSideEffects = false;
 }
+
+// Pseudo equivalent to a RISCVISD::VSLIDEDOWN_VL
+def G_VSLIDEDOWN_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_VSLIDEDOWN_VL, riscv_slidedown_vl>;
+
diff --git a/llvm/test/CodeGen/RISCV/GlobalISel/legalizer/rvv/legalize-extract-subvector.mir b/llvm/test/CodeGen/RISCV/GlobalISel/legalizer/rvv/legalize-extract-subvector.mir
new file mode 100644
index 00000000000000..78a2f82632d96a
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/GlobalISel/legalizer/rvv/legalize-extract-subvector.mir
@@ -0,0 +1,339 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=riscv32 -mattr=+v -run-pass=legalizer %s -o - | FileCheck %s --check-prefixes=CHECK,RV32
+# RUN: llc -mtriple=riscv64 -mattr=+v -run-pass=legalizer %s -o - | FileCheck %s --check-prefixes=CHECK,RV64
+
+# Special handling for i1-element vectors with non-zero index
+---
+name:            extract_subvector_nxv4i1
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; RV32-LABEL: name: extract_subvector_nxv4i1
+    ; RV32: [[DEF:%[0-9]+]]:_(<vscale x 4 x s1>) = G_IMPLICIT_DEF
+    ; RV32-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV32-NEXT: [[SPLAT_VECTOR:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SPLAT_VECTOR [[C]](s32)
+    ; RV32-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; RV32-NEXT: [[SPLAT_VECTOR1:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SPLAT_VECTOR [[C1]](s32)
+    ; RV32-NEXT: [[SELECT:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SELECT [[DEF]](<vscale x 4 x s1>), [[SPLAT_VECTOR1]], [[SPLAT_VECTOR]]
+    ; RV32-NEXT: [[READ_VLENB:%[0-9]+]]:_(s32) = G_READ_VLENB
+    ; RV32-NEXT: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 2
+    ; RV32-NEXT: [[LSHR:%[0-9]+]]:_(s32) = G_LSHR [[READ_VLENB]], [[C2]](s32)
+    ; RV32-NEXT: [[VMSET_VL:%[0-9]+]]:_(<vscale x 2 x s1>) = G_VMSET_VL $x0
+    ; RV32-NEXT: [[DEF1:%[0-9]+]]:_(<vscale x 4 x s8>) = G_IMPLICIT_DEF
+    ; RV32-NEXT: [[VSLIDEDOWN_VL:%[0-9]+]]:_(<vscale x 4 x s8>) = G_VSLIDEDOWN_VL [[DEF1]], [[SELECT]], [[LSHR]](s32), [[VMSET_VL]](<vscale x 2 x s1>), $x0, 3
+    ; RV32-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 2 x s8>) = G_EXTRACT_SUBVECTOR [[VSLIDEDOWN_VL]](<vscale x 4 x s8>), 0
+    ; RV32-NEXT: [[BITCAST:%[0-9]+]]:_(<vscale x 2 x s8>) = G_BITCAST [[EXTRACT_SUBVECTOR]](<vscale x 2 x s8>)
+    ; RV32-NEXT: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV32-NEXT: [[SPLAT_VECTOR2:%[0-9]+]]:_(<vscale x 2 x s8>) = G_SPLAT_VECTOR [[C3]](s32)
+    ; RV32-NEXT: [[ICMP:%[0-9]+]]:_(<vscale x 2 x s1>) = G_ICMP intpred(ne), [[BITCAST]](<vscale x 2 x s8>), [[SPLAT_VECTOR2]]
+    ; RV32-NEXT: $v8 = COPY [[ICMP]](<vscale x 2 x s1>)
+    ; RV32-NEXT: PseudoRET implicit $v8
+    ;
+    ; RV64-LABEL: name: extract_subvector_nxv4i1
+    ; RV64: [[DEF:%[0-9]+]]:_(<vscale x 4 x s1>) = G_IMPLICIT_DEF
+    ; RV64-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV64-NEXT: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[C]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SPLAT_VECTOR [[ANYEXT]](s64)
+    ; RV64-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; RV64-NEXT: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[C1]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR1:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SPLAT_VECTOR [[ANYEXT1]](s64)
+    ; RV64-NEXT: [[SELECT:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SELECT [[DEF]](<vscale x 4 x s1>), [[SPLAT_VECTOR1]], [[SPLAT_VECTOR]]
+    ; RV64-NEXT: [[READ_VLENB:%[0-9]+]]:_(s64) = G_READ_VLENB
+    ; RV64-NEXT: [[C2:%[0-9]+]]:_(s64) = G_CONSTANT i64 2
+    ; RV64-NEXT: [[LSHR:%[0-9]+]]:_(s64) = G_LSHR [[READ_VLENB]], [[C2]](s64)
+    ; RV64-NEXT: [[VMSET_VL:%[0-9]+]]:_(<vscale x 2 x s1>) = G_VMSET_VL $x0
+    ; RV64-NEXT: [[DEF1:%[0-9]+]]:_(<vscale x 4 x s8>) = G_IMPLICIT_DEF
+    ; RV64-NEXT: [[VSLIDEDOWN_VL:%[0-9]+]]:_(<vscale x 4 x s8>) = G_VSLIDEDOWN_VL [[DEF1]], [[SELECT]], [[LSHR]](s64), [[VMSET_VL]](<vscale x 2 x s1>), $x0, 3
+    ; RV64-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 2 x s8>) = G_EXTRACT_SUBVECTOR [[VSLIDEDOWN_VL]](<vscale x 4 x s8>), 0
+    ; RV64-NEXT: [[BITCAST:%[0-9]+]]:_(<vscale x 2 x s8>) = G_BITCAST [[EXTRACT_SUBVECTOR]](<vscale x 2 x s8>)
+    ; RV64-NEXT: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV64-NEXT: [[ANYEXT2:%[0-9]+]]:_(s64) = G_ANYEXT [[C3]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR2:%[0-9]+]]:_(<vscale x 2 x s8>) = G_SPLAT_VECTOR [[ANYEXT2]](s64)
+    ; RV64-NEXT: [[ICMP:%[0-9]+]]:_(<vscale x 2 x s1>) = G_ICMP intpred(ne), [[BITCAST]](<vscale x 2 x s8>), [[SPLAT_VECTOR2]]
+    ; RV64-NEXT: $v8 = COPY [[ICMP]](<vscale x 2 x s1>)
+    ; RV64-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 4 x s1>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 2 x s1>) = G_EXTRACT_SUBVECTOR %0(<vscale x 4 x s1>), 2
+    $v8 = COPY %1(<vscale x 2 x s1>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv8i1
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; RV32-LABEL: name: extract_subvector_nxv8i1
+    ; RV32: [[DEF:%[0-9]+]]:_(<vscale x 8 x s1>) = G_IMPLICIT_DEF
+    ; RV32-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV32-NEXT: [[SPLAT_VECTOR:%[0-9]+]]:_(<vscale x 8 x s8>) = G_SPLAT_VECTOR [[C]](s32)
+    ; RV32-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; RV32-NEXT: [[SPLAT_VECTOR1:%[0-9]+]]:_(<vscale x 8 x s8>) = G_SPLAT_VECTOR [[C1]](s32)
+    ; RV32-NEXT: [[SELECT:%[0-9]+]]:_(<vscale x 8 x s8>) = G_SELECT [[DEF]](<vscale x 8 x s1>), [[SPLAT_VECTOR1]], [[SPLAT_VECTOR]]
+    ; RV32-NEXT: [[READ_VLENB:%[0-9]+]]:_(s32) = G_READ_VLENB
+    ; RV32-NEXT: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 2
+    ; RV32-NEXT: [[LSHR:%[0-9]+]]:_(s32) = G_LSHR [[READ_VLENB]], [[C2]](s32)
+    ; RV32-NEXT: [[VMSET_VL:%[0-9]+]]:_(<vscale x 2 x s1>) = G_VMSET_VL $x0
+    ; RV32-NEXT: [[DEF1:%[0-9]+]]:_(<vscale x 8 x s8>) = G_IMPLICIT_DEF
+    ; RV32-NEXT: [[VSLIDEDOWN_VL:%[0-9]+]]:_(<vscale x 8 x s8>) = G_VSLIDEDOWN_VL [[DEF1]], [[SELECT]], [[LSHR]](s32), [[VMSET_VL]](<vscale x 2 x s1>), $x0, 3
+    ; RV32-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 2 x s8>) = G_EXTRACT_SUBVECTOR [[VSLIDEDOWN_VL]](<vscale x 8 x s8>), 0
+    ; RV32-NEXT: [[BITCAST:%[0-9]+]]:_(<vscale x 2 x s8>) = G_BITCAST [[EXTRACT_SUBVECTOR]](<vscale x 2 x s8>)
+    ; RV32-NEXT: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV32-NEXT: [[SPLAT_VECTOR2:%[0-9]+]]:_(<vscale x 2 x s8>) = G_SPLAT_VECTOR [[C3]](s32)
+    ; RV32-NEXT: [[ICMP:%[0-9]+]]:_(<vscale x 2 x s1>) = G_ICMP intpred(ne), [[BITCAST]](<vscale x 2 x s8>), [[SPLAT_VECTOR2]]
+    ; RV32-NEXT: $v8 = COPY [[ICMP]](<vscale x 2 x s1>)
+    ; RV32-NEXT: PseudoRET implicit $v8
+    ;
+    ; RV64-LABEL: name: extract_subvector_nxv8i1
+    ; RV64: [[DEF:%[0-9]+]]:_(<vscale x 8 x s1>) = G_IMPLICIT_DEF
+    ; RV64-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV64-NEXT: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[C]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR:%[0-9]+]]:_(<vscale x 8 x s8>) = G_SPLAT_VECTOR [[ANYEXT]](s64)
+    ; RV64-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; RV64-NEXT: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[C1]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR1:%[0-9]+]]:_(<vscale x 8 x s8>) = G_SPLAT_VECTOR [[ANYEXT1]](s64)
+    ; RV64-NEXT: [[SELECT:%[0-9]+]]:_(<vscale x 8 x s8>) = G_SELECT [[DEF]](<vscale x 8 x s1>), [[SPLAT_VECTOR1]], [[SPLAT_VECTOR]]
+    ; RV64-NEXT: [[READ_VLENB:%[0-9]+]]:_(s64) = G_READ_VLENB
+    ; RV64-NEXT: [[C2:%[0-9]+]]:_(s64) = G_CONSTANT i64 2
+    ; RV64-NEXT: [[LSHR:%[0-9]+]]:_(s64) = G_LSHR [[READ_VLENB]], [[C2]](s64)
+    ; RV64-NEXT: [[VMSET_VL:%[0-9]+]]:_(<vscale x 2 x s1>) = G_VMSET_VL $x0
+    ; RV64-NEXT: [[DEF1:%[0-9]+]]:_(<vscale x 8 x s8>) = G_IMPLICIT_DEF
+    ; RV64-NEXT: [[VSLIDEDOWN_VL:%[0-9]+]]:_(<vscale x 8 x s8>) = G_VSLIDEDOWN_VL [[DEF1]], [[SELECT]], [[LSHR]](s64), [[VMSET_VL]](<vscale x 2 x s1>), $x0, 3
+    ; RV64-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 2 x s8>) = G_EXTRACT_SUBVECTOR [[VSLIDEDOWN_VL]](<vscale x 8 x s8>), 0
+    ; RV64-NEXT: [[BITCAST:%[0-9]+]]:_(<vscale x 2 x s8>) = G_BITCAST [[EXTRACT_SUBVECTOR]](<vscale x 2 x s8>)
+    ; RV64-NEXT: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV64-NEXT: [[ANYEXT2:%[0-9]+]]:_(s64) = G_ANYEXT [[C3]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR2:%[0-9]+]]:_(<vscale x 2 x s8>) = G_SPLAT_VECTOR [[ANYEXT2]](s64)
+    ; RV64-NEXT: [[ICMP:%[0-9]+]]:_(<vscale x 2 x s1>) = G_ICMP intpred(ne), [[BITCAST]](<vscale x 2 x s8>), [[SPLAT_VECTOR2]]
+    ; RV64-NEXT: $v8 = COPY [[ICMP]](<vscale x 2 x s1>)
+    ; RV64-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 8 x s1>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 2 x s1>) = G_EXTRACT_SUBVECTOR %0(<vscale x 8 x s1>), 2
+    $v8 = COPY %1(<vscale x 2 x s1>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv64i1
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; RV32-LABEL: name: extract_subvector_nxv64i1
+    ; RV32: [[DEF:%[0-9]+]]:_(<vscale x 64 x s1>) = G_IMPLICIT_DEF
+    ; RV32-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV32-NEXT: [[SPLAT_VECTOR:%[0-9]+]]:_(<vscale x 64 x s8>) = G_SPLAT_VECTOR [[C]](s32)
+    ; RV32-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; RV32-NEXT: [[SPLAT_VECTOR1:%[0-9]+]]:_(<vscale x 64 x s8>) = G_SPLAT_VECTOR [[C1]](s32)
+    ; RV32-NEXT: [[SELECT:%[0-9]+]]:_(<vscale x 64 x s8>) = G_SELECT [[DEF]](<vscale x 64 x s1>), [[SPLAT_VECTOR1]], [[SPLAT_VECTOR]]
+    ; RV32-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 4 x s8>) = G_EXTRACT_SUBVECTOR [[SELECT]](<vscale x 64 x s8>), 16
+    ; RV32-NEXT: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV32-NEXT: [[SPLAT_VECTOR2:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SPLAT_VECTOR [[C2]](s32)
+    ; RV32-NEXT: [[ICMP:%[0-9]+]]:_(<vscale x 4 x s1>) = G_ICMP intpred(ne), [[EXTRACT_SUBVECTOR]](<vscale x 4 x s8>), [[SPLAT_VECTOR2]]
+    ; RV32-NEXT: $v8 = COPY [[ICMP]](<vscale x 4 x s1>)
+    ; RV32-NEXT: PseudoRET implicit $v8
+    ;
+    ; RV64-LABEL: name: extract_subvector_nxv64i1
+    ; RV64: [[DEF:%[0-9]+]]:_(<vscale x 64 x s1>) = G_IMPLICIT_DEF
+    ; RV64-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV64-NEXT: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[C]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR:%[0-9]+]]:_(<vscale x 64 x s8>) = G_SPLAT_VECTOR [[ANYEXT]](s64)
+    ; RV64-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; RV64-NEXT: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[C1]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR1:%[0-9]+]]:_(<vscale x 64 x s8>) = G_SPLAT_VECTOR [[ANYEXT1]](s64)
+    ; RV64-NEXT: [[SELECT:%[0-9]+]]:_(<vscale x 64 x s8>) = G_SELECT [[DEF]](<vscale x 64 x s1>), [[SPLAT_VECTOR1]], [[SPLAT_VECTOR]]
+    ; RV64-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 4 x s8>) = G_EXTRACT_SUBVECTOR [[SELECT]](<vscale x 64 x s8>), 16
+    ; RV64-NEXT: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; RV64-NEXT: [[ANYEXT2:%[0-9]+]]:_(s64) = G_ANYEXT [[C2]](s32)
+    ; RV64-NEXT: [[SPLAT_VECTOR2:%[0-9]+]]:_(<vscale x 4 x s8>) = G_SPLAT_VECTOR [[ANYEXT2]](s64)
+    ; RV64-NEXT: [[ICMP:%[0-9]+]]:_(<vscale x 4 x s1>) = G_ICMP intpred(ne), [[EXTRACT_SUBVECTOR]](<vscale x 4 x s8>), [[SPLAT_VECTOR2]]
+    ; RV64-NEXT: $v8 = COPY [[ICMP]](<vscale x 4 x s1>)
+    ; RV64-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 64 x s1>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 4 x s1>) = G_EXTRACT_SUBVECTOR %0(<vscale x 64 x s1>), 16
+    $v8 = COPY %1(<vscale x 4 x s1>)
+    PseudoRET implicit $v8
+...
+
+# i1-element vectors with zero index
+---
+name:            extract_subvector_nxv4i1_zero
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv4i1_zero
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 4 x s1>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 1 x s1>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 4 x s1>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 1 x s1>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 4 x s1>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 1 x s1>) = G_EXTRACT_SUBVECTOR %0(<vscale x 4 x s1>), 0
+    $v8 = COPY %1(<vscale x 1 x s1>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv8i1_zero
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv8i1_zero
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 8 x s1>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 4 x s1>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 8 x s1>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 4 x s1>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 8 x s1>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 4 x s1>) = G_EXTRACT_SUBVECTOR %0(<vscale x 8 x s1>), 0
+    $v8 = COPY %1(<vscale x 4 x s1>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv64i1_zero
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv64i1_zero
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 64 x s1>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 32 x s1>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 64 x s1>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 32 x s1>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 64 x s1>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 32 x s1>) = G_EXTRACT_SUBVECTOR %0(<vscale x 64 x s1>), 0
+    $v8 = COPY %1(<vscale x 32 x s1>)
+    PseudoRET implicit $v8
+...
+
+# Extract with zero index
+---
+name:            extract_subvector_nxv2i8_zero
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv2i8_zero
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 2 x s8>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 1 x s8>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 2 x s8>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 1 x s8>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 2 x s8>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 1 x s8>) = G_EXTRACT_SUBVECTOR %0(<vscale x 2 x s8>), 0
+    $v8 = COPY %1(<vscale x 1 x s8>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv4i16_zero
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv4i16_zero
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 4 x s16>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 2 x s16>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 4 x s16>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 2 x s16>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 4 x s16>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 2 x s16>) = G_EXTRACT_SUBVECTOR %0(<vscale x 4 x s16>), 0
+    $v8 = COPY %1(<vscale x 2 x s16>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv8i32_zero
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv8i32_zero
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 8 x s32>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 4 x s32>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 8 x s32>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 4 x s32>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 8 x s32>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 4 x s32>) = G_EXTRACT_SUBVECTOR %0(<vscale x 8 x s32>), 0
+    $v8 = COPY %1(<vscale x 4 x s32>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv8i64_zero
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv8i64_zero
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 8 x s64>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 4 x s64>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 8 x s64>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 4 x s64>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 8 x s64>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 4 x s64>) = G_EXTRACT_SUBVECTOR %0(<vscale x 8 x s64>), 0
+    $v8 = COPY %1(<vscale x 4 x s64>)
+    PseudoRET implicit $v8
+...
+
+# Extract with non-zero index
+---
+name:            extract_subvector_nxv2i8
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv2i8
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 2 x s8>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 1 x s8>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 2 x s8>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 1 x s8>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 2 x s8>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 1 x s8>) = G_EXTRACT_SUBVECTOR %0(<vscale x 2 x s8>), 0
+    $v8 = COPY %1(<vscale x 1 x s8>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv4i16
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv4i16
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 4 x s16>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 1 x s16>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 4 x s16>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 1 x s16>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 4 x s16>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 1 x s16>) = G_EXTRACT_SUBVECTOR %0(<vscale x 4 x s16>), 0
+    $v8 = COPY %1(<vscale x 1 x s16>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv8i32
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv8i32
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 8 x s32>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 4 x s32>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 8 x s32>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 4 x s32>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 8 x s32>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 4 x s32>) = G_EXTRACT_SUBVECTOR %0(<vscale x 8 x s32>), 0
+    $v8 = COPY %1(<vscale x 4 x s32>)
+    PseudoRET implicit $v8
+...
+---
+name:            extract_subvector_nxv8i64
+legalized:       false
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: extract_subvector_nxv8i64
+    ; CHECK: [[DEF:%[0-9]+]]:_(<vscale x 8 x s64>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[EXTRACT_SUBVECTOR:%[0-9]+]]:_(<vscale x 2 x s64>) = G_EXTRACT_SUBVECTOR [[DEF]](<vscale x 8 x s64>), 0
+    ; CHECK-NEXT: $v8 = COPY [[EXTRACT_SUBVECTOR]](<vscale x 2 x s64>)
+    ; CHECK-NEXT: PseudoRET implicit $v8
+    %0:_(<vscale x 8 x s64>) = G_IMPLICIT_DEF
+    %1:_(<vscale x 2 x s64>) = G_EXTRACT_SUBVECTOR %0(<vscale x 8 x s64>), 0
+    $v8 = COPY %1(<vscale x 2 x s64>)
+    PseudoRET implicit $v8
+...
+



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