diff --git a/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp b/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
--- a/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
@@ -3240,6 +3240,63 @@
   ReplaceNode(N, N3);
 }
 
+// NOTE: We cannot use EXTRACT_SUBREG in all cases because the fixed length
+// vector types larger than NEON don't have a matching SubRegIndex.
+static SDNode *extractSubReg(SelectionDAG *DAG, EVT VT, SDValue V) {
+  assert(V.getValueType().isScalableVector() &&
+         V.getValueType().getSizeInBits().getKnownMinSize() ==
+             AArch64::SVEBitsPerBlock &&
+         "Expected to extract from a packed scalable vector!");
+  assert(VT.isFixedLengthVector() &&
+         "Expected to extract a fixed length vector!");
+
+  SDLoc DL(V);
+  switch (VT.getSizeInBits()) {
+  case 64: {
+    auto SubReg = DAG->getTargetConstant(AArch64::dsub, DL, MVT::i32);
+    return DAG->getMachineNode(TargetOpcode::EXTRACT_SUBREG, DL, VT, V, SubReg);
+  }
+  case 128: {
+    auto SubReg = DAG->getTargetConstant(AArch64::zsub, DL, MVT::i32);
+    return DAG->getMachineNode(TargetOpcode::EXTRACT_SUBREG, DL, VT, V, SubReg);
+  }
+  default: {
+    auto RC = DAG->getTargetConstant(AArch64::ZPRRegClassID, DL, MVT::i64);
+    return DAG->getMachineNode(TargetOpcode::COPY_TO_REGCLASS, DL, VT, V, RC);
+  }
+  }
+}
+
+// NOTE: We cannot use INSERT_SUBREG in all cases because the fixed length
+// vector types larger than NEON don't have a matching SubRegIndex.
+static SDNode *insertSubReg(SelectionDAG *DAG, EVT VT, SDValue V) {
+  assert(VT.isScalableVector() &&
+         VT.getSizeInBits().getKnownMinSize() == AArch64::SVEBitsPerBlock &&
+         "Expected to insert into a packed scalable vector!");
+  assert(V.getValueType().isFixedLengthVector() &&
+         "Expected to insert a fixed length vector!");
+
+  SDLoc DL(V);
+  switch (V.getValueType().getSizeInBits()) {
+  case 64: {
+    auto SubReg = DAG->getTargetConstant(AArch64::dsub, DL, MVT::i32);
+    auto Container = DAG->getMachineNode(TargetOpcode::IMPLICIT_DEF, DL, VT);
+    return DAG->getMachineNode(TargetOpcode::INSERT_SUBREG, DL, VT,
+                               SDValue(Container, 0), V, SubReg);
+  }
+  case 128: {
+    auto SubReg = DAG->getTargetConstant(AArch64::zsub, DL, MVT::i32);
+    auto Container = DAG->getMachineNode(TargetOpcode::IMPLICIT_DEF, DL, VT);
+    return DAG->getMachineNode(TargetOpcode::INSERT_SUBREG, DL, VT,
+                               SDValue(Container, 0), V, SubReg);
+  }
+  default: {
+    auto RC = DAG->getTargetConstant(AArch64::ZPRRegClassID, DL, MVT::i64);
+    return DAG->getMachineNode(TargetOpcode::COPY_TO_REGCLASS, DL, VT, V, RC);
+  }
+  }
+}
+
 void AArch64DAGToDAGISel::Select(SDNode *Node) {
   // If we have a custom node, we already have selected!
   if (Node->isMachineOpcode()) {
@@ -3313,6 +3370,52 @@
       return;
     break;
 
+  case ISD::EXTRACT_SUBVECTOR: {
+    // Bail when not a "cast" like extract_subvector.
+    if (cast<ConstantSDNode>(Node->getOperand(1))->getZExtValue() != 0)
+      break;
+
+    // Bail when normal isel can do the job.
+    EVT InVT = Node->getOperand(0).getValueType();
+    if (VT.isScalableVector() || InVT.isFixedLengthVector())
+      break;
+
+    // NOTE: We can only get here when doing fixed length SVE code generation.
+    // We do manual selection because the types involved are not linked to real
+    // registers (despite being legal) and must be coerced into SVE registers.
+    //
+    // NOTE: If the above changes, be aware that selection will still not work
+    // because the td definition of extract_vector does not support extracting
+    // a fixed length vector from a scalable vector.
+
+    ReplaceNode(Node, extractSubReg(CurDAG, VT, Node->getOperand(0)));
+    return;
+  }
+
+  case ISD::INSERT_SUBVECTOR: {
+    // Bail when not a "cast" like insert_subvector.
+    if (cast<ConstantSDNode>(Node->getOperand(2))->getZExtValue() != 0)
+      break;
+    if (!Node->getOperand(0).isUndef())
+      break;
+
+    // Bail when normal isel should do the job.
+    EVT InVT = Node->getOperand(1).getValueType();
+    if (VT.isFixedLengthVector() || InVT.isScalableVector())
+      break;
+
+    // NOTE: We can only get here when doing fixed length SVE code generation.
+    // We do manual selection because the types involved are not linked to real
+    // registers (despite being legal) and must be coerced into SVE registers.
+    //
+    // NOTE: If the above changes, be aware that selection will still not work
+    // because the td definition of insert_vector does not support inserting a
+    // fixed length vector into a scalable vector.
+
+    ReplaceNode(Node, insertSubReg(CurDAG, VT, Node->getOperand(1)));
+    return;
+  }
+
   case ISD::Constant: {
     // Materialize zero constants as copies from WZR/XZR.  This allows
     // the coalescer to propagate these into other instructions.
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.h b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.h
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.h
@@ -846,6 +846,7 @@
   SDValue LowerToPredicatedOp(SDValue Op, SelectionDAG &DAG,
                               unsigned NewOp) const;
   SDValue LowerEXTRACT_SUBVECTOR(SDValue Op, SelectionDAG &DAG) const;
+  SDValue LowerINSERT_SUBVECTOR(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerVectorSRA_SRL_SHL(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerShiftLeftParts(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerShiftRightParts(SDValue Op, SelectionDAG &DAG) const;
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -116,6 +116,18 @@
 /// Value type used for condition codes.
 static const MVT MVT_CC = MVT::i32;
 
+/// Returns true if VT's elements occupy the lowest bit positions of its
+/// associated register class without any intervening space.
+///
+/// For example, nxv2f16, nxv4f16 and nxv8f16 are legal types that belong to the
+/// same register class, but only nxv8f16 can be treated as a packed vector.
+static inline bool isPackedVectorType(EVT VT, SelectionDAG &DAG) {
+  assert(VT.isVector() && DAG.getTargetLoweringInfo().isTypeLegal(VT) &&
+         "Expected legal vector type!");
+  return VT.isFixedLengthVector() ||
+         VT.getSizeInBits().getKnownMinSize() == AArch64::SVEBitsPerBlock;
+}
+
 AArch64TargetLowering::AArch64TargetLowering(const TargetMachine &TM,
                                              const AArch64Subtarget &STI)
     : TargetLowering(TM), Subtarget(&STI) {
@@ -906,6 +918,7 @@
     // D68877 for more details.
     for (MVT VT : MVT::integer_scalable_vector_valuetypes()) {
       if (isTypeLegal(VT)) {
+        setOperationAction(ISD::INSERT_SUBVECTOR, VT, Custom);
         setOperationAction(ISD::SPLAT_VECTOR, VT, Custom);
         setOperationAction(ISD::SELECT, VT, Custom);
         setOperationAction(ISD::SDIV, VT, Custom);
@@ -919,16 +932,18 @@
         setOperationAction(ISD::SRA, VT, Custom);
         if (VT.getScalarType() == MVT::i1)
           setOperationAction(ISD::SETCC, VT, Custom);
-      } else {
-        for (auto VT : { MVT::nxv8i8, MVT::nxv4i16, MVT::nxv2i32 })
-          setOperationAction(ISD::EXTRACT_SUBVECTOR, VT, Custom);
       }
     }
+
+    for (auto VT : {MVT::nxv8i8, MVT::nxv4i16, MVT::nxv2i32})
+      setOperationAction(ISD::EXTRACT_SUBVECTOR, VT, Custom);
+
     setOperationAction(ISD::INTRINSIC_WO_CHAIN, MVT::i8, Custom);
     setOperationAction(ISD::INTRINSIC_WO_CHAIN, MVT::i16, Custom);
 
     for (MVT VT : MVT::fp_scalable_vector_valuetypes()) {
       if (isTypeLegal(VT)) {
+        setOperationAction(ISD::INSERT_SUBVECTOR, VT, Custom);
         setOperationAction(ISD::SPLAT_VECTOR, VT, Custom);
         setOperationAction(ISD::SELECT, VT, Custom);
       }
@@ -1035,9 +1050,7 @@
   for (unsigned Op = 0; Op < ISD::BUILTIN_OP_END; ++Op)
     setOperationAction(Op, VT, Expand);
 
-  // EXTRACT_SUBVECTOR/INSERT_SUBVECTOR are used to "cast" between scalable
-  // and fixed length vector types, although with the current level of support
-  // only the former is exercised.
+  // We use EXTRACT_SUBVECTOR to "cast" a scalable vector to a fixed length one.
   setOperationAction(ISD::EXTRACT_SUBVECTOR, VT, Custom);
 
   // Lower fixed length vector operations to scalable equivalents.
@@ -3457,6 +3470,8 @@
     return LowerSPLAT_VECTOR(Op, DAG);
   case ISD::EXTRACT_SUBVECTOR:
     return LowerEXTRACT_SUBVECTOR(Op, DAG);
+  case ISD::INSERT_SUBVECTOR:
+    return LowerINSERT_SUBVECTOR(Op, DAG);
   case ISD::SDIV:
     return LowerToPredicatedOp(Op, DAG, AArch64ISD::SDIV_PRED);
   case ISD::UDIV:
@@ -8665,29 +8680,47 @@
 
 SDValue AArch64TargetLowering::LowerEXTRACT_SUBVECTOR(SDValue Op,
                                                       SelectionDAG &DAG) const {
-  assert(!Op.getValueType().isScalableVector() &&
-         "Unexpected scalable type for custom lowering EXTRACT_SUBVECTOR");
+  assert(Op.getValueType().isFixedLengthVector() &&
+         "Only cases that extract a fixed length vector are supported!");
 
-  EVT VT = Op.getOperand(0).getValueType();
-  SDLoc dl(Op);
-  // Just in case...
-  if (!VT.isVector())
-    return SDValue();
+  EVT InVT = Op.getOperand(0).getValueType();
+  unsigned Idx = cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
+  unsigned Size = Op.getValueSizeInBits();
 
-  ConstantSDNode *Cst = dyn_cast<ConstantSDNode>(Op.getOperand(1));
-  if (!Cst)
-    return SDValue();
-  unsigned Val = Cst->getZExtValue();
+  if (InVT.isScalableVector()) {
+    // This will be matched by custom code during ISelDAGToDAG.
+    if (Idx == 0 && isPackedVectorType(InVT, DAG))
+      return Op;
 
-  unsigned Size = Op.getValueSizeInBits();
+    return SDValue();
+  }
 
   // This will get lowered to an appropriate EXTRACT_SUBREG in ISel.
-  if (Val == 0)
+  if (Idx == 0 && InVT.getSizeInBits() <= 128)
     return Op;
 
   // If this is extracting the upper 64-bits of a 128-bit vector, we match
   // that directly.
-  if (Size == 64 && Val * VT.getScalarSizeInBits() == 64)
+  if (Size == 64 && Idx * InVT.getScalarSizeInBits() == 64)
+    return Op;
+
+  return SDValue();
+}
+
+SDValue AArch64TargetLowering::LowerINSERT_SUBVECTOR(SDValue Op,
+                                                     SelectionDAG &DAG) const {
+  assert(Op.getValueType().isScalableVector() &&
+         "Only expect to lower inserts into scalable vectors!");
+
+  EVT InVT = Op.getOperand(1).getValueType();
+  unsigned Idx = cast<ConstantSDNode>(Op.getOperand(2))->getZExtValue();
+
+  // We don't have any patterns for scalable vector yet.
+  if (InVT.isScalableVector() || !useSVEForFixedLengthVectorVT(InVT))
+    return SDValue();
+
+  // This will be matched by custom code during ISelDAGToDAG.
+  if (Idx == 0 && isPackedVectorType(InVT, DAG) && Op.getOperand(0).isUndef())
     return Op;
 
   return SDValue();
diff --git a/llvm/test/CodeGen/AArch64/sve-fixed-length-subvector.ll b/llvm/test/CodeGen/AArch64/sve-fixed-length-subvector.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/sve-fixed-length-subvector.ll
@@ -0,0 +1,88 @@
+; RUN: llc -aarch64-sve-vector-bits-min=128  -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefix=NO_SVE
+; RUN: llc -aarch64-sve-vector-bits-min=256  -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK
+; RUN: llc -aarch64-sve-vector-bits-min=384  -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK
+; RUN: llc -aarch64-sve-vector-bits-min=512  -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512
+; RUN: llc -aarch64-sve-vector-bits-min=640  -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512
+; RUN: llc -aarch64-sve-vector-bits-min=768  -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512
+; RUN: llc -aarch64-sve-vector-bits-min=896  -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512
+; RUN: llc -aarch64-sve-vector-bits-min=1024 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=1152 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=1280 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=1408 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=1536 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=1664 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=1792 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=1920 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
+; RUN: llc -aarch64-sve-vector-bits-min=2048 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024,VBITS_GE_2048
+
+; Test we can code generater patterns of the form:
+;   fixed_length_vector = ISD::EXTRACT_SUBVECTOR scalable_vector, 0
+;   scalable_vector = ISD::INSERT_SUBVECTOR scalable_vector, fixed_length_vector, 0
+;
+; NOTE: Currently shufflevector does not support scalable vectors so it cannot
+; be used to model the above operations.  Instead these tests rely on knowing
+; how fixed length operation are lowered to scalable ones, with multiple blocks
+; ensuring insert/extract sequences are not folded away.
+
+target triple = "aarch64-unknown-linux-gnu"
+
+; Don't use SVE when its registers are no bigger than NEON.
+; NO_SVE-NOT: ptrue
+
+define void @subvector_v8i32(<8 x i32> *%in, <8 x i32>* %out) #0 {
+; CHECK-LABEL: subvector_v8i32:
+; CHECK: ptrue [[PG:p[0-9]+]].s, vl8
+; CHECK: ld1w { [[DATA:z[0-9]+.s]] }, [[PG]]/z, [x0]
+; CHECK: st1w { [[DATA]] }, [[PG]], [x1]
+; CHECK: ret
+  %a = load <8 x i32>, <8 x i32>* %in
+  br label %bb1
+
+bb1:
+  store <8 x i32> %a, <8 x i32>* %out
+  ret void
+}
+
+define void @subvector_v16i32(<16 x i32> *%in, <16 x i32>* %out) #0 {
+; CHECK-LABEL: subvector_v16i32:
+; VBITS_GE_512: ptrue [[PG:p[0-9]+]].s, vl16
+; VBITS_GE_512: ld1w { [[DATA:z[0-9]+.s]] }, [[PG]]/z, [x0]
+; VBITS_GE_512: st1w { [[DATA]] }, [[PG]], [x1]
+; CHECKT: ret
+  %a = load <16 x i32>, <16 x i32>* %in
+  br label %bb1
+
+bb1:
+  store <16 x i32> %a, <16 x i32>* %out
+  ret void
+}
+
+define void @subvector_v32i32(<32 x i32> *%in, <32 x i32>* %out) #0 {
+; CHECK-LABEL: subvector_v32i32:
+; VBITS_GE_1024: ptrue [[PG:p[0-9]+]].s, vl32
+; VBITS_GE_1024: ld1w { [[DATA:z[0-9]+.s]] }, [[PG]]/z, [x0]
+; VBITS_GE_1024: st1w { [[DATA]] }, [[PG]], [x1]
+; CHECK: ret
+  %a = load <32 x i32>, <32 x i32>* %in
+  br label %bb1
+
+bb1:
+  store <32 x i32> %a, <32 x i32>* %out
+  ret void
+}
+
+define void @subvector_v64i32(<64 x i32> *%in, <64 x i32>* %out) #0 {
+; CHECK-LABEL: subvector_v64i32:
+; VBITS_GE_2048: ptrue [[PG:p[0-9]+]].s, vl64
+; VBITS_GE_2048: ld1w { [[DATA:z[0-9]+.s]] }, [[PG]]/z, [x0]
+; VBITS_GE_2048: st1w { [[DATA]] }, [[PG]], [x1]
+; CHECK: ret
+  %a = load <64 x i32>, <64 x i32>* %in
+  br label %bb1
+
+bb1:
+  store <64 x i32> %a, <64 x i32>* %out
+  ret void
+}
+
+attributes #0 = { "target-features"="+sve" }