[SelectionDAG] Make WidenVecRes_EXTRACT_SUBVECTOR work for scalable vectors.

[sdesmalen]

Summary

The legalizer handles this by breaking up an EXTRACT_SUBVECTOR into
smaller parts, and combines those together, padding the result with
UNDEF vectors, e.g.

nxv6i64 extract_subvector(nxv12i64, 6)
<->
nxv8i64 concat(
  nxv2i64 extract_subvector(nxv16i64, 6)
  nxv2i64 extract_subvector(nxv16i64, 8)
  nxv2i64 extract_subvector(nxv16i64, 10)
  nxv2i64 undef)

[david-arm]

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

4108

Hi @sdesmalen, I think we're assuming here that IdxVal is always going to be a multiple of GCD, which may be true. However, I wonder if it's worth adding an assert for this to ensure we're always following the lang ref for EXTRACT_SUBVECTOR.

[sdesmalen]

Added assert for Idx.

[sdesmalen]

Rebased patch onto D110523 (which means the tests have changed)

[david-arm]

LGTM! The extract_nxv6f16_nxv12f16_6 test looks right now, thanks @sdesmalen! I haven't gone through the predicate tests because it's a nightmare, but since the fp16 tests look right I assume the algorithm is correct for predicates too.

[frasercrmck]

I'd be interested in seeing some RISCV tests to improve the coverage (but I won't block on it)

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

4117

Nit: is this message too general now? It implies we can't do anything, ever.

[sdesmalen]

In D110253#3023769, @frasercrmck wrote:

I'd be interested in seeing some RISCV tests to improve the coverage (but I won't block on it)

I'm happy to add a test, just wasn't entirely sure what types are legal for RVV. Would the same extract <vscale x 6 x half> from <vscale x 12 x half> be suitable?

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

4117

Ah that wasn't my intention, I meant it more as "the code as it is today doesn't know how to widen the result of extract_subvector for scalable vectors". I think the message is correct though, since LLVM doesn't know how to widen it and it avoids falling into the fixed-width code below.

[frasercrmck]

In D110253#3023789, @sdesmalen wrote:

In D110253#3023769, @frasercrmck wrote:

I'd be interested in seeing some RISCV tests to improve the coverage (but I won't block on it)

I'm happy to add a test, just wasn't entirely sure what types are legal for RVV. Would the same extract <vscale x 6 x half> from <vscale x 12 x half> be suitable?

Thanks, yeah that'd need widening. Broadly speaking all power-of-two element counts 1+ are either legal or will need splitting. Anything else will be widened. We don't have bfloat though.

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

4117

Hmm, from my perspective it's just that this method is WidenVecRes_EXTRACT_SUBVECTOR and this patch is enabling it to widen the result of extract_subvector for scalable vectors -- at least for those where the part doesn't also need widening. I agree there needs to be a fatal error here, just I thought that a user seeing this error may think something else is going on. I dunno, I may have missed the mark here.

[sdesmalen]

Added a similar test for RVV.

[frasercrmck]

LGTM, thanks for adding some RVV tests, @sdesmalen.

llvm/test/CodeGen/RISCV/rvv/extract-subvector.ll

486

I'm not sure this vslideup.vi is completely necessary but I think it's correct.

[sdesmalen]

Cheers for the review @frasercrmck and @david-arm!

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp

SDValue DAGTypeLegalizer::WidenVecRes_CONCAT_VECTORS(SDNode *N) {
   SDValue UndefVal = DAG.getUNDEF(EltVT);
   for (; Idx < WidenNumElts; ++Idx)
     Ops[Idx] = UndefVal;
   return DAG.getBuildVector(WidenVT, dl, Ops);
 }
 
 SDValue DAGTypeLegalizer::WidenVecRes_EXTRACT_SUBVECTOR(SDNode *N) {
   EVT      VT = N->getValueType(0);
+  EVT      EltVT = VT.getVectorElementType();
   EVT      WidenVT = TLI.getTypeToTransformTo(*DAG.getContext(), VT);
   SDValue  InOp = N->getOperand(0);
   SDValue  Idx  = N->getOperand(1);
   SDLoc dl(N);
 
-  if (getTypeAction(InOp.getValueType()) == TargetLowering::TypeWidenVector)
+  auto InOpTypeAction = getTypeAction(InOp.getValueType());
+  if (InOpTypeAction == TargetLowering::TypeWidenVector)
     InOp = GetWidenedVector(InOp);
 
   EVT InVT = InOp.getValueType();
 
   // Check if we can just return the input vector after widening.
   uint64_t IdxVal = cast<ConstantSDNode>(Idx)->getZExtValue();
   if (IdxVal == 0 && InVT == WidenVT)
     return InOp;
 
-  if (VT.isScalableVector())
-    report_fatal_error("Don't know how to widen the result of "
-                       "EXTRACT_SUBVECTOR for scalable vectors");
-
   // Check if we can extract from the vector.
-  unsigned WidenNumElts = WidenVT.getVectorNumElements();
-  unsigned InNumElts = InVT.getVectorNumElements();
+  unsigned WidenNumElts = WidenVT.getVectorMinNumElements();
+  unsigned InNumElts = InVT.getVectorMinNumElements();
   if (IdxVal % WidenNumElts == 0 && IdxVal + WidenNumElts < InNumElts)
     return DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, WidenVT, InOp, Idx);
 
+  if (VT.isScalableVector()) {
+    // Try to split the operation up into smaller extracts and concat the
+    // results together, e.g.
+    //    nxv6i64 extract_subvector(nxv12i64, 6)
+    // <->
+    //  nxv8i64 concat(
+    //    nxv2i64 extract_subvector(nxv16i64, 6)
+    //    nxv2i64 extract_subvector(nxv16i64, 8)
+    //    nxv2i64 extract_subvector(nxv16i64, 10)
+    //    undef)
+    unsigned VTNElts = VT.getVectorMinNumElements();
+    unsigned GCD = greatestCommonDivisor(VTNElts, WidenNumElts);
+    assert((IdxVal % GCD) == 0 && "Expected Idx to be a multiple of the broken "
+                                  "down type's element count");
+    EVT PartVT = EVT::getVectorVT(*DAG.getContext(), EltVT,
+                                  ElementCount::getScalable(GCD));
+    // Avoid recursion around e.g. nxv1i8.
+    if (getTypeAction(PartVT) != TargetLowering::TypeWidenVector) {
+      SmallVector<SDValue> Parts;
+      unsigned I = 0;
+      for (; I < VTNElts / GCD; ++I)
+        Parts.push_back(
+            DAG.getNode(ISD::EXTRACT_SUBVECTOR, dl, PartVT, InOp,
+                        DAG.getVectorIdxConstant(IdxVal + I * GCD, dl)));
+      for (; I < WidenNumElts / GCD; ++I)
+        Parts.push_back(DAG.getUNDEF(PartVT));
+
+      return DAG.getNode(ISD::CONCAT_VECTORS, dl, WidenVT, Parts);
+    }
+
+    report_fatal_error("Don't know how to widen the result of "
+                       "EXTRACT_SUBVECTOR for scalable vectors");
+  }
+
   // We could try widening the input to the right length but for now, extract
   // the original elements, fill the rest with undefs and build a vector.
   SmallVector<SDValue, 16> Ops(WidenNumElts);
-  EVT EltVT = VT.getVectorElementType();
   unsigned NumElts = VT.getVectorNumElements();
   unsigned i;
   for (i = 0; i < NumElts; ++i)
     Ops[i] = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, EltVT, InOp,
                          DAG.getVectorIdxConstant(IdxVal + i, dl));
 
   SDValue UndefVal = DAG.getUNDEF(EltVT);
   for (; i < WidenNumElts; ++i)

llvm/test/CodeGen/AArch64/sve-extract-scalable-vector.ll

 ; CHECK-NEXT:    ret
   %res = call <vscale x 8 x i1> @llvm.experimental.vector.extract.nxv8i1.nxv16i1(<vscale x 16 x i1> %in, i64 8)
   ret <vscale x 8 x i1> %res
 }
 
 declare <vscale x 8 x i1> @llvm.experimental.vector.extract.nxv8i1.nxv16i1(<vscale x 16 x i1>, i64)
 
 ;
+; Extract i1 vector that needs widening from one that needs widening.
+;
+define <vscale x 14 x i1> @extract_nxv14i1_nxv28i1_0(<vscale x 28 x i1> %in) {
+; CHECK-LABEL: extract_nxv14i1_nxv28i1_0:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
+  %res = call <vscale x 14 x i1> @llvm.experimental.vector.extract.nxv14i1.nxv28i1(<vscale x 28 x i1> %in, i64 0)
+  ret <vscale x 14 x i1> %res
+}
+
+define <vscale x 14 x i1> @extract_nxv14i1_nxv28i1_14(<vscale x 28 x i1> %in) {
+; CHECK-LABEL: extract_nxv14i1_nxv28i1_14:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    str x29, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-NEXT:    addvl sp, sp, #-1
+; CHECK-NEXT:    str p5, [sp, #6, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT:    str p4, [sp, #7, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT:    .cfi_escape 0x0f, 0x0c, 0x8f, 0x00, 0x11, 0x10, 0x22, 0x11, 0x08, 0x92, 0x2e, 0x00, 0x1e, 0x22 // sp + 16 + 8 * VG
+; CHECK-NEXT:    .cfi_offset w29, -16
+; CHECK-NEXT:    punpkhi p2.h, p1.b
+; CHECK-NEXT:    punpklo p1.h, p1.b
+; CHECK-NEXT:    punpkhi p0.h, p0.b
+; CHECK-NEXT:    punpklo p2.h, p2.b
+; CHECK-NEXT:    punpkhi p3.h, p1.b
+; CHECK-NEXT:    punpkhi p0.h, p0.b
+; CHECK-NEXT:    punpklo p1.h, p1.b
+; CHECK-NEXT:    punpkhi p4.h, p2.b
+; CHECK-NEXT:    punpklo p2.h, p2.b
+; CHECK-NEXT:    punpkhi p5.h, p3.b
+; CHECK-NEXT:    punpkhi p0.h, p0.b
+; CHECK-NEXT:    punpklo p3.h, p3.b
+; CHECK-NEXT:    uzp1 p2.s, p5.s, p2.s
+; CHECK-NEXT:    punpkhi p5.h, p1.b
+; CHECK-NEXT:    punpklo p1.h, p1.b
+; CHECK-NEXT:    uzp1 p4.s, p4.s, p0.s
+; CHECK-NEXT:    uzp1 p3.s, p5.s, p3.s
+; CHECK-NEXT:    uzp1 p0.s, p0.s, p1.s
+; CHECK-NEXT:    uzp1 p1.h, p2.h, p4.h
+; CHECK-NEXT:    ldr p5, [sp, #6, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT:    ldr p4, [sp, #7, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT:    uzp1 p0.h, p0.h, p3.h
+; CHECK-NEXT:    uzp1 p0.b, p0.b, p1.b
+; CHECK-NEXT:    addvl sp, sp, #1
+; CHECK-NEXT:    ldr x29, [sp], #16 // 8-byte Folded Reload
+; CHECK-NEXT:    ret
+  %res = call <vscale x 14 x i1> @llvm.experimental.vector.extract.nxv14i1.nxv28i1(<vscale x 28 x i1> %in, i64 14)
+  ret <vscale x 14 x i1> %res
+}
+
+declare <vscale x 14 x i1> @llvm.experimental.vector.extract.nxv14i1.nxv28i1(<vscale x 28 x i1>, i64)
+
+;
 ; Extract half i1 vector that needs promotion from one that needs splitting.
 ;
 define <vscale x 8 x i1> @extract_nxv8i1_nxv32i1_0(<vscale x 32 x i1> %in) {
 ; CHECK-LABEL: extract_nxv8i1_nxv32i1_0:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    punpklo p0.h, p0.b
 ; CHECK-NEXT:    ret
   %res = call <vscale x 8 x i1> @llvm.experimental.vector.extract.nxv8i1.nxv32i1(<vscale x 32 x i1> %in, i64 0)

 ; CHECK-NEXT:    ret
   %res = call <vscale x 8 x i8> @llvm.experimental.vector.extract.nxv8i8.nxv16i8(<vscale x 16 x i8> %in, i64 8)
   ret <vscale x 8 x i8> %res
 }
 
 declare <vscale x 8 x i8> @llvm.experimental.vector.extract.nxv8i8.nxv16i8(<vscale x 16 x i8>, i64)
 
 ;
+; Extract i8 vector that needs widening from one that needs widening.
+;
+define <vscale x 14 x i8> @extract_nxv14i8_nxv28i8_0(<vscale x 28 x i8> %in) {
+; CHECK-LABEL: extract_nxv14i8_nxv28i8_0:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
+  %res = call <vscale x 14 x i8> @llvm.experimental.vector.extract.nxv14i8.nxv28i8(<vscale x 28 x i8> %in, i64 0)
+  ret <vscale x 14 x i8> %res
+}
+
+define <vscale x 14 x i8> @extract_nxv14i8_nxv28i8_14(<vscale x 28 x i8> %in) {
+; CHECK-LABEL: extract_nxv14i8_nxv28i8_14:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    uunpkhi z0.h, z0.b
+; CHECK-NEXT:    uunpkhi z0.s, z0.h
+; CHECK-NEXT:    uunpkhi z0.d, z0.s
+; CHECK-NEXT:    uzp1 z0.s, z0.s, z0.s
+; CHECK-NEXT:    uzp1 z0.h, z0.h, z0.h
+; CHECK-NEXT:    uzp1 z0.b, z0.b, z0.b
+; CHECK-NEXT:    uunpklo z2.h, z1.b
+; CHECK-NEXT:    uunpklo z0.h, z0.b
+; CHECK-NEXT:    uunpklo z3.s, z2.h
+; CHECK-NEXT:    uunpklo z5.s, z0.h
+; CHECK-NEXT:    uunpklo z4.d, z3.s
+; CHECK-NEXT:    uunpklo z5.d, z5.s
+; CHECK-NEXT:    uzp1 z4.s, z5.s, z4.s
+; CHECK-NEXT:    uunpkhi z0.s, z0.h
+; CHECK-NEXT:    uzp1 z0.h, z4.h, z0.h
+; CHECK-NEXT:    uzp1 z0.b, z0.b, z0.b
+; CHECK-NEXT:    uunpklo z0.h, z0.b
+; CHECK-NEXT:    uunpkhi z4.s, z0.h
+; CHECK-NEXT:    uunpkhi z3.d, z3.s
+; CHECK-NEXT:    uunpkhi z4.d, z4.s
+; CHECK-NEXT:    uzp1 z3.s, z3.s, z4.s
+; CHECK-NEXT:    uunpklo z0.s, z0.h
+; CHECK-NEXT:    uzp1 z0.h, z0.h, z3.h
+; CHECK-NEXT:    uzp1 z0.b, z0.b, z0.b
+; CHECK-NEXT:    uunpklo z0.h, z0.b
+; CHECK-NEXT:    uunpkhi z2.s, z2.h
+; CHECK-NEXT:    uunpkhi z3.s, z0.h
+; CHECK-NEXT:    uunpklo z5.d, z2.s
+; CHECK-NEXT:    uunpklo z3.d, z3.s
+; CHECK-NEXT:    uunpklo z0.s, z0.h
+; CHECK-NEXT:    uzp1 z3.s, z3.s, z5.s
+; CHECK-NEXT:    uzp1 z0.h, z0.h, z3.h
+; CHECK-NEXT:    uzp1 z3.b, z0.b, z0.b
+; CHECK-NEXT:    uunpkhi z3.h, z3.b
+; CHECK-NEXT:    uunpklo z5.s, z3.h
+; CHECK-NEXT:    uunpkhi z2.d, z2.s
+; CHECK-NEXT:    uunpkhi z5.d, z5.s
+; CHECK-NEXT:    uunpkhi z3.s, z3.h
+; CHECK-NEXT:    uzp1 z2.s, z2.s, z5.s
+; CHECK-NEXT:    uzp1 z2.h, z2.h, z3.h
+; CHECK-NEXT:    uzp1 z2.b, z0.b, z2.b
+; CHECK-NEXT:    uunpkhi z1.h, z1.b
+; CHECK-NEXT:    uunpkhi z2.h, z2.b
+; CHECK-NEXT:    uunpklo z1.s, z1.h
+; CHECK-NEXT:    uunpklo z3.s, z2.h
+; CHECK-NEXT:    uunpklo z4.d, z1.s
+; CHECK-NEXT:    uunpklo z3.d, z3.s
+; CHECK-NEXT:    uunpkhi z2.s, z2.h
+; CHECK-NEXT:    uzp1 z3.s, z3.s, z4.s
+; CHECK-NEXT:    uzp1 z2.h, z3.h, z2.h
+; CHECK-NEXT:    uzp1 z2.b, z0.b, z2.b
+; CHECK-NEXT:    uunpkhi z2.h, z2.b
+; CHECK-NEXT:    uunpkhi z3.s, z2.h
+; CHECK-NEXT:    uunpkhi z1.d, z1.s
+; CHECK-NEXT:    uunpkhi z3.d, z3.s
+; CHECK-NEXT:    uunpklo z2.s, z2.h
+; CHECK-NEXT:    uzp1 z1.s, z1.s, z3.s
+; CHECK-NEXT:    uzp1 z1.h, z2.h, z1.h
+; CHECK-NEXT:    uzp1 z1.b, z0.b, z1.b
+; CHECK-NEXT:    uunpkhi z1.h, z1.b
+; CHECK-NEXT:    uunpkhi z2.s, z1.h
+; CHECK-NEXT:    uunpklo z2.d, z2.s
+; CHECK-NEXT:    uzp1 z2.s, z2.s, z0.s
+; CHECK-NEXT:    uunpklo z1.s, z1.h
+; CHECK-NEXT:    uzp1 z1.h, z1.h, z2.h
+; CHECK-NEXT:    uzp1 z0.b, z0.b, z1.b
+; CHECK-NEXT:    ret
+  %res = call <vscale x 14 x i8> @llvm.experimental.vector.extract.nxv14i8.nxv28i8(<vscale x 28 x i8> %in, i64 14)
+  ret <vscale x 14 x i8> %res
+}
+
+declare <vscale x 14 x i8> @llvm.experimental.vector.extract.nxv14i8.nxv28i8(<vscale x 28 x i8>, i64)
+
+;
 ; Extract 1/4th i8 vector that needs promotion from legal type.
 ;
 define <vscale x 4 x i8> @extract_nxv4i8_nxv16i8_0(<vscale x 16 x i8> %in) {
 ; CHECK-LABEL: extract_nxv4i8_nxv16i8_0:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    uunpklo z0.h, z0.b
 ; CHECK-NEXT:    uunpklo z0.s, z0.h
 ; CHECK-NEXT:    ret

 ; CHECK-NEXT:    ret
   %res = call <vscale x 4 x half> @llvm.experimental.vector.extract.nxv4f16.nxv8f16(<vscale x 8 x half> %in, i64 4)
   ret <vscale x 4 x half> %res
 }
 
 declare <vscale x 4 x half> @llvm.experimental.vector.extract.nxv4f16.nxv8f16(<vscale x 8 x half>, i64)
 
 ;
+; Extract f16 vector that needs widening from one that needs widening.
+;
+define <vscale x 6 x half> @extract_nxv6f16_nxv12f16_0(<vscale x 12 x half> %in) {
+; CHECK-LABEL: extract_nxv6f16_nxv12f16_0:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
+  %res = call <vscale x 6 x half> @llvm.experimental.vector.extract.nxv6f16.nxv12f16(<vscale x 12 x half> %in, i64 0)
+  ret <vscale x 6 x half> %res
+}
+
+define <vscale x 6 x half> @extract_nxv6f16_nxv12f16_6(<vscale x 12 x half> %in) {
+; CHECK-LABEL: extract_nxv6f16_nxv12f16_6:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    uunpklo z1.s, z1.h
+; CHECK-NEXT:    uunpkhi z0.s, z0.h
+; CHECK-NEXT:    uunpkhi z2.d, z1.s
+; CHECK-NEXT:    uunpklo z1.d, z1.s
+; CHECK-NEXT:    uunpkhi z0.d, z0.s
+; CHECK-NEXT:    uzp1 z2.s, z2.s, z0.s
+; CHECK-NEXT:    uzp1 z0.s, z0.s, z1.s
+; CHECK-NEXT:    uzp1 z0.h, z0.h, z2.h
+; CHECK-NEXT:    ret
+  %res = call <vscale x 6 x half> @llvm.experimental.vector.extract.nxv6f16.nxv12f16(<vscale x 12 x half> %in, i64 6)
+  ret <vscale x 6 x half> %res
+}
+
+declare <vscale x 6 x half> @llvm.experimental.vector.extract.nxv6f16.nxv12f16(<vscale x 12 x half>, i64)
+
+;
 ; Extract half f16 vector that needs promotion from one that needs splitting.
 ;
 define <vscale x 4 x half> @extract_nxv4f16_nxv16f16_0(<vscale x 16 x half> %in) {
 ; CHECK-LABEL: extract_nxv4f16_nxv16f16_0:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    uunpklo z0.s, z0.h
 ; CHECK-NEXT:    ret
   %res = call <vscale x 4 x half> @llvm.experimental.vector.extract.nxv4f16.nxv16f16(<vscale x 16 x half> %in, i64 0)

 ; CHECK-NEXT:    ret
   %res = call <vscale x 4 x bfloat> @llvm.experimental.vector.extract.nxv4bf16.nxv8bf16(<vscale x 8 x bfloat> %in, i64 4)
   ret <vscale x 4 x bfloat> %res
 }
 
 declare <vscale x 4 x bfloat> @llvm.experimental.vector.extract.nxv4bf16.nxv8bf16(<vscale x 8 x bfloat>, i64)
 
 ;
+; Extract bf16 vector that needs widening from one that needs widening.
+;
+define <vscale x 6 x bfloat> @extract_nxv6bf16_nxv12bf16_0(<vscale x 12 x bfloat> %in) {
+; CHECK-LABEL: extract_nxv6bf16_nxv12bf16_0:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    ret
+  %res = call <vscale x 6 x bfloat> @llvm.experimental.vector.extract.nxv6bf16.nxv12bf16(<vscale x 12 x bfloat> %in, i64 0)
+  ret <vscale x 6 x bfloat> %res
+}
+
+define <vscale x 6 x bfloat> @extract_nxv6bf16_nxv12bf16_6(<vscale x 12 x bfloat> %in) {
+; CHECK-LABEL: extract_nxv6bf16_nxv12bf16_6:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    uunpklo z1.s, z1.h
+; CHECK-NEXT:    uunpkhi z0.s, z0.h
+; CHECK-NEXT:    uunpkhi z2.d, z1.s
+; CHECK-NEXT:    uunpklo z1.d, z1.s
+; CHECK-NEXT:    uunpkhi z0.d, z0.s
+; CHECK-NEXT:    uzp1 z2.s, z2.s, z0.s
+; CHECK-NEXT:    uzp1 z0.s, z0.s, z1.s
+; CHECK-NEXT:    uzp1 z0.h, z0.h, z2.h
+; CHECK-NEXT:    ret
+  %res = call <vscale x 6 x bfloat> @llvm.experimental.vector.extract.nxv6bf16.nxv12bf16(<vscale x 12 x bfloat> %in, i64 6)
+  ret <vscale x 6 x bfloat> %res
+}
+
+declare <vscale x 6 x bfloat> @llvm.experimental.vector.extract.nxv6bf16.nxv12bf16(<vscale x 12 x bfloat>, i64)
+
+;
 ; Extract bf16 vector that needs promotion from one that needs widening.
 ;
 define <vscale x 2 x bfloat> @extract_nxv2bf16_nxv6bf16_0(<vscale x 6 x bfloat> %in) {
 ; CHECK-LABEL: extract_nxv2bf16_nxv6bf16_0:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    uunpklo z0.s, z0.h
 ; CHECK-NEXT:    uunpklo z0.d, z0.s
 ; CHECK-NEXT:    ret

llvm/test/CodeGen/RISCV/rvv/extract-subvector.ll

 ; CHECK-NEXT:    srli a0, a0, 2
 ; CHECK-NEXT:    vsetvli a1, zero, e8, mf2, ta, mu
 ; CHECK-NEXT:    vslidedown.vx v0, v0, a0
 ; CHECK-NEXT:    ret
   %c = call <vscale x 16 x i1> @llvm.experimental.vector.extract.nxv16i1(<vscale x 32 x i1> %x, i64 16)
   ret <vscale x 16 x i1> %c
 }
 
+;
+; Extract f16 vector that needs widening from one that needs widening.
+;
+define <vscale x 6 x half> @extract_nxv6f16_nxv12f16_0(<vscale x 12 x half> %in) {
+; CHECK-LABEL: extract_nxv6f16_nxv12f16_0:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    # kill: def $v8m2 killed $v8m2 killed $v8m4
+; CHECK-NEXT:    ret
+  %res = call <vscale x 6 x half> @llvm.experimental.vector.extract.nxv6f16.nxv12f16(<vscale x 12 x half> %in, i64 0)
+  ret <vscale x 6 x half> %res
+}
+
+define <vscale x 6 x half> @extract_nxv6f16_nxv12f16_6(<vscale x 12 x half> %in) {
+; CHECK-LABEL: extract_nxv6f16_nxv12f16_6:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    csrr a0, vlenb
+; CHECK-NEXT:    srli a0, a0, 2
+; CHECK-NEXT:    vsetvli a1, zero, e16, m1, ta, mu
+; CHECK-NEXT:    vslidedown.vx v25, v10, a0
+; CHECK-NEXT:    vslidedown.vx v26, v9, a0
+; CHECK-NEXT:    vsetvli zero, a0, e16, m1, tu, mu
+; CHECK-NEXT:    vslideup.vi v27, v25, 0
+; CHECK-NEXT:    add a1, a0, a0
+; CHECK-NEXT:    vsetvli zero, a1, e16, m1, tu, mu
+; CHECK-NEXT:    vslideup.vx v27, v25, a0
+; CHECK-NEXT:    vslideup.vx v26, v10, a0
+; CHECK-NEXT:    vmv2r.v v8, v26
+; CHECK-NEXT:    ret
+  %res = call <vscale x 6 x half> @llvm.experimental.vector.extract.nxv6f16.nxv12f16(<vscale x 12 x half> %in, i64 6)
+  ret <vscale x 6 x half> %res
+}
+
+declare <vscale x 6 x half> @llvm.experimental.vector.extract.nxv6f16.nxv12f16(<vscale x 12 x half>, i64)
+
 declare <vscale x 1 x i8> @llvm.experimental.vector.extract.nxv1i8.nxv4i8(<vscale x 4 x i8> %vec, i64 %idx)
 declare <vscale x 1 x i8> @llvm.experimental.vector.extract.nxv1i8.nxv8i8(<vscale x 8 x i8> %vec, i64 %idx)
 
 declare <vscale x 2 x i8> @llvm.experimental.vector.extract.nxv2i8.nxv32i8(<vscale x 32 x i8> %vec, i64 %idx)
 
 declare <vscale x 1 x i32> @llvm.experimental.vector.extract.nxv1i32.nxv2i32(<vscale x 2 x i32> %vec, i64 %idx)
 
 declare <vscale x 2 x i32> @llvm.experimental.vector.extract.nxv2i32.nxv8i32(<vscale x 8 x i32> %vec, i64 %idx)