[DAGCombiner][VP] Add DAGCombine for VP_MUL.

[jacquesguan]

Summary

This patch uses visitMUL to combine VP_MUL, shares most logic of MUL with VP_MUL.

[RKSimon]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22858

(style) Don't use auto unless the type is obvious (i.e. a cast<>)

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22858

Don't call isConstOrConstSplat(N1) twice

22860

What about mul by positive 1 or 0?

[jacquesguan]

Address comment.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22858

Done.

22860

Done.

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22861

If one of the true/false values of the VP_SELECT is undef can we ignore the mask and EVL and return the other operand? @simoll @frasercrmck

[simoll]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22861

I believe so. Also for vp ops other than select or merge, if the mask is undef, we can scratch the operation entirely. If evl is undef, we can cut short to unreachable.

[jacquesguan]

Address comment.

[jacquesguan]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22861

Done, thanks.

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22863

I think we should only use getSplatVector for scalable vectors. Fixed vectors should use getSplatBuildVector.

22863

You can just call DAG.getConstant(0, SDLoc(N), VT); It will do the right thing.

22874

DAG.getConstant(0, SDLoc(N), VT)

22882

Same comment as above.

[jacquesguan]

Address comment.

[jacquesguan]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

22863

Done.

22874

Done.

22882

Done.

[simoll]

@jacquesguan Thanks for working on VP optimizations! We just discussed on the VP syncup call where we want to go with this.
The thing is that this patch is essentially replicating the existing MUL DAGCombiner patterns for VP_MUL. Ideally, we would lift the existing DAGCombiner logic to work on both VP and non-VP SDNodes - automatically.

I've implemented something like this in NEC's open source LLVM stack:
https://github.com/sx-aurora-dev/llvm-project/blob/develop/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

The idea is to templatize the pattern-matching and rewriting code and instantiate that for each VP and non-VP. In essence, https://reviews.llvm.org/D92086 but on the SelectionDAG.

Would you be interested in working on a more general approach? Please contact me directly so we can get you on the VP Discord server or arrange a call to talk about this.

[jacquesguan]

reuse visitMUL to combine VP_MUL.

[jacquesguan]

fix comment.

[craig.topper]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

3887

IS -> Is

3893

What does it mean to support a VP op in FoldConstantArithmetic?

[jacquesguan]

Address comment.

[jacquesguan]

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

3893

I was thinking wrong. This TODO is removed now.

[jacquesguan]

ping.

[jacquesguan]

ping.

[jacquesguan]

ping.

[jacquesguan]

ping...

[craig.topper]

I'm concerned about the number of checks for IsVP. It looks like maybe this function will be hard to maintain in the future. Every new change will have to think about whether it works for VP. Most LLVM developers don't care about VP so may miss this detail.

[jacquesguan]

In D121187#4582381, @craig.topper wrote:

I'm concerned about the number of checks for IsVP. It looks like maybe this function will be hard to maintain in the future. Every new change will have to think about whether it works for VP. Most LLVM developers don't care about VP so may miss this detail.

Yes, it is a problem, and even we remove all IsVP in the function, a developper that wants to change this function should also think about whether the change works on VP version too. Actually I used a new function visitVP_MUL to implement the combination of VP_MUL at begining, and @simoll suggested to make the existed logic work on both no-vp and vp ops, so I switch to this way. Do you think which one is a better solution, reuse the visitMUL or create a new visitVP_MUL with some repeat code?

[jacquesguan]

ping

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

private:
     SDValue visitMLOAD(SDNode *N);
     SDValue visitMSTORE(SDNode *N);
     SDValue visitMGATHER(SDNode *N);
     SDValue visitMSCATTER(SDNode *N);
     SDValue visitFP_TO_FP16(SDNode *N);
     SDValue visitFP16_TO_FP(SDNode *N);
     SDValue visitVECREDUCE(SDNode *N);
     SDValue visitVPOp(SDNode *N);
+    SDValue visitVP_MUL(SDNode *N);
 
     SDValue visitFADDForFMACombine(SDNode *N);
     SDValue visitFSUBForFMACombine(SDNode *N);
     SDValue visitFMULForFMADistributiveCombine(SDNode *N);
 
     SDValue XformToShuffleWithZero(SDNode *N);
     bool reassociationCanBreakAddressingModePattern(unsigned Opc,
                                                     const SDLoc &DL, SDValue N0,
SDValue DAGCombiner::visitMULFIX(SDNode *N) {
 
   return SDValue();
 }
 
 SDValue DAGCombiner::visitMUL(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
   EVT VT = N0.getValueType();
 
   // fold (mul x, undef) -> 0
   if (N0.isUndef() || N1.isUndef())
     return DAG.getConstant(0, SDLoc(N), VT);
 
   // fold (mul c1, c2) -> c1*c2
   if (SDValue C = DAG.FoldConstantArithmetic(ISD::MUL, SDLoc(N), VT, {N0, N1}))
     return C;
 
   // canonicalize constant to RHS (vector doesn't have to splat)
   if (DAG.isConstantIntBuildVectorOrConstantInt(N0) &&
       !DAG.isConstantIntBuildVectorOrConstantInt(N1))
     return DAG.getNode(ISD::MUL, SDLoc(N), VT, N1, N0);
 
   bool N1IsConst = false;
if ((Opcode == ISD::VECREDUCE_OR &&
         (Opcode == ISD::VECREDUCE_AND &&
          (N0.getOperand(0).isUndef() || isAllOnesOrAllOnesSplat(Vec))))
       return DAG.getNode(Opcode, SDLoc(N), N->getValueType(0), Subvec);
   }
 
   return SDValue();
 }
 
+SDValue DAGCombiner::visitVP_MUL(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  SDValue Mask = N->getOperand(2);
+  SDValue EVL = N->getOperand(3);
+  EVT VT = N0.getValueType();
+
+  ConstantSDNode *ConstValue0 = isConstOrConstSplat(N0);
+  ConstantSDNode *ConstValue1 = isConstOrConstSplat(N1);
+
+  // canonicalize constant splat to RHS
+  if (ConstValue0 && !ConstValue1)
+    return DAG.getNode(ISD::VP_MUL, SDLoc(N), VT, N1, N0, Mask, EVL);
+
+  // fold vp_mul X, (splat 0), Mask, EVL -> splat 0
+  if (ConstValue1 && ConstValue1->isZero()) {
+    return DAG.getSplatVector(
+        VT, SDLoc(N),
+        DAG.getConstant(0, SDLoc(N), ConstValue1->getValueType(0)));
+  }
+
+  // fold vp_mul X, (splat 1), Mask, EVL -> X
+  if (ConstValue1 && ConstValue1->isOne())
+    return N0;
+
+  // fold vp_mul X, (splat -1), Mask, EVL -> vp_sub (splat 0), X, Mask, EVL
+  if (ConstValue1 && ConstValue1->isAllOnes()) {
+    SDValue ZeroSplat = DAG.getSplatVector(
+        VT, SDLoc(N),
+        DAG.getConstant(0, SDLoc(N), ConstValue1->getValueType(0)));
+    return DAG.getNode(ISD::VP_SUB, SDLoc(N), VT, ZeroSplat, N0, Mask, EVL);
+  }
+
+  // fold vp_mul X, (1 << C), Mask, EVL -> vp_shl X, C, Mask, EVL
+  if (ConstValue1 && ConstValue1->getAPIntValue().isPowerOf2()) {
+    SDValue Splat = DAG.getSplatVector(
+        VT, SDLoc(N),
+        DAG.getConstant(ConstValue1->getAPIntValue().countTrailingZeros(),
+                        SDLoc(N), ConstValue1->getValueType(0)));
+    return DAG.getNode(ISD::VP_SHL, SDLoc(N), VT, N0, Splat, Mask, EVL);
+  }
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitVPOp(SDNode *N) {
   // VP operations in which all vector elements are disabled - either by
   // determining that the mask is all false or that the EVL is 0 - can be
   // eliminated.
   bool AreAllEltsDisabled = false;
   if (auto EVLIdx = ISD::getVPExplicitVectorLengthIdx(N->getOpcode()))
     AreAllEltsDisabled |= isNullConstant(N->getOperand(*EVLIdx));
   if (auto MaskIdx = ISD::getVPMaskIdx(N->getOpcode()))
     AreAllEltsDisabled |=
         ISD::isConstantSplatVectorAllZeros(N->getOperand(*MaskIdx).getNode());
 
   // This is the only generic VP combine we support for now.
-  if (!AreAllEltsDisabled)
+  if (!AreAllEltsDisabled) {
+    switch (N->getOpcode()) {
+    case ISD::VP_MUL:
+      return visitVP_MUL(N);
+    // TODO: Support more VP op.
+    default:
+      break;
+    }
     return SDValue();
+  }
 
   // Binary operations can be replaced by UNDEF.
   if (ISD::isVPBinaryOp(N->getOpcode()))
     return DAG.getUNDEF(N->getValueType(0));
 
   // VP Memory operations can be replaced by either the chain (stores) or the
   // chain + undef (loads).
   if (const auto *MemSD = dyn_cast<MemSDNode>(N)) {

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-vmul-vp.ll

 ; RV64-NEXT:    ret
   %elt.head = insertelement <16 x i64> poison, i64 %b, i32 0
   %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
   %head = insertelement <16 x i1> poison, i1 true, i32 0
   %m = shufflevector <16 x i1> %head, <16 x i1> poison, <16 x i32> zeroinitializer
   %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
   ret <16 x i64> %v
 }
+
+define <16 x i64> @vmul_vx_1_v16i64(<16 x i64> %va, <16 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_1_v16i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vrsub.vi v8, v8, 0, v0.t
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 -1, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}
+
+define <16 x i64> @vmul_vx_1_v16i64_unmasked(<16 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_1_v16i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vrsub.vi v8, v8, 0
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 -1, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %head = insertelement <16 x i1> poison, i1 true, i32 0
+  %m = shufflevector <16 x i1> %head, <16 x i1> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}
+
+define <16 x i64> @vmul_vx_2_v16i64(<16 x i64> %va, <16 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_2_v16i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vsll.vi v8, v8, 6, v0.t
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 64, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}
+
+define <16 x i64> @vmul_vx_2_v16i64_unmasked(<16 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_2_v16i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vsll.vi v8, v8, 6
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 64, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %head = insertelement <16 x i1> poison, i1 true, i32 0
+  %m = shufflevector <16 x i1> %head, <16 x i1> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}
+
+define <16 x i64> @vmul_vx_3_v16i64(<16 x i64> %va, <16 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_3_v16i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 1, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}
+
+define <16 x i64> @vmul_vx_3_v16i64_unmasked(<16 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_3_v16i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 1, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %head = insertelement <16 x i1> poison, i1 true, i32 0
+  %m = shufflevector <16 x i1> %head, <16 x i1> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}
+
+define <16 x i64> @vmul_vx_4_v16i64(<16 x i64> %va, <16 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_4_v16i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetivli zero, 16, e64, m8, ta, mu
+; CHECK-NEXT:    vmv.v.i v8, 0
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 0, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}
+
+define <16 x i64> @vmul_vx_4_v16i64_unmasked(<16 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_4_v16i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetivli zero, 16, e64, m8, ta, mu
+; CHECK-NEXT:    vmv.v.i v8, 0
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <16 x i64> poison, i64 0, i32 0
+  %vb = shufflevector <16 x i64> %elt.head, <16 x i64> poison, <16 x i32> zeroinitializer
+  %head = insertelement <16 x i1> poison, i1 true, i32 0
+  %m = shufflevector <16 x i1> %head, <16 x i1> poison, <16 x i32> zeroinitializer
+  %v = call <16 x i64> @llvm.vp.mul.v16i64(<16 x i64> %va, <16 x i64> %vb, <16 x i1> %m, i32 %evl)
+  ret <16 x i64> %v
+}

llvm/test/CodeGen/RISCV/rvv/vmul-vp.ll

 ; RV64-NEXT:    ret
   %elt.head = insertelement <vscale x 8 x i64> poison, i64 %b, i32 0
   %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
   %head = insertelement <vscale x 8 x i1> poison, i1 true, i32 0
   %m = shufflevector <vscale x 8 x i1> %head, <vscale x 8 x i1> poison, <vscale x 8 x i32> zeroinitializer
   %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
   ret <vscale x 8 x i64> %v
 }
+
+define <vscale x 8 x i64> @vmul_vx_1_nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_1_nxv8i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vrsub.vi v8, v8, 0, v0.t
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 -1, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}
+
+define <vscale x 8 x i64> @vmul_vx_1_nxv8i64_unmasked(<vscale x 8 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_1_nxv8i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vrsub.vi v8, v8, 0
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 -1, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %head = insertelement <vscale x 8 x i1> poison, i1 true, i32 0
+  %m = shufflevector <vscale x 8 x i1> %head, <vscale x 8 x i1> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}
+
+define <vscale x 8 x i64> @vmul_vx_2_nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_2_nxv8i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vsll.vi v8, v8, 6, v0.t
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 64, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}
+
+define <vscale x 8 x i64> @vmul_vx_2_nxv8i64_unmasked(<vscale x 8 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_2_nxv8i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli zero, a0, e64, m8, ta, mu
+; CHECK-NEXT:    vsll.vi v8, v8, 6
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 64, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %head = insertelement <vscale x 8 x i1> poison, i1 true, i32 0
+  %m = shufflevector <vscale x 8 x i1> %head, <vscale x 8 x i1> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}
+
+define <vscale x 8 x i64> @vmul_vx_3_nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_3_nxv8i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 1, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}
+
+define <vscale x 8 x i64> @vmul_vx_3_nxv8i64_unmasked(<vscale x 8 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_3_nxv8i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 1, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %head = insertelement <vscale x 8 x i1> poison, i1 true, i32 0
+  %m = shufflevector <vscale x 8 x i1> %head, <vscale x 8 x i1> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}
+
+
+define <vscale x 8 x i64> @vmul_vx_4_nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i1> %m, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_4_nxv8i64:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli a0, zero, e64, m8, ta, mu
+; CHECK-NEXT:    vmv.v.i v8, 0
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 0, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}
+
+define <vscale x 8 x i64> @vmul_vx_4_nxv8i64_unmasked(<vscale x 8 x i64> %va, i32 zeroext %evl) {
+; CHECK-LABEL: vmul_vx_4_nxv8i64_unmasked:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli a0, zero, e64, m8, ta, mu
+; CHECK-NEXT:    vmv.v.i v8, 0
+; CHECK-NEXT:    ret
+  %elt.head = insertelement <vscale x 8 x i64> poison, i64 0, i32 0
+  %vb = shufflevector <vscale x 8 x i64> %elt.head, <vscale x 8 x i64> poison, <vscale x 8 x i32> zeroinitializer
+  %head = insertelement <vscale x 8 x i1> poison, i1 true, i32 0
+  %m = shufflevector <vscale x 8 x i1> %head, <vscale x 8 x i1> poison, <vscale x 8 x i32> zeroinitializer
+  %v = call <vscale x 8 x i64> @llvm.vp.mul.nxv8i64(<vscale x 8 x i64> %va, <vscale x 8 x i64> %vb, <vscale x 8 x i1> %m, i32 %evl)
+  ret <vscale x 8 x i64> %v
+}