[RISCV] Disable matchSplatAsGather for i1 vectors to prevent creating illegal nodes.

[craig.topper]

Summary

We were incorrectly creating a VRGATHER node with i1 vector type. We
could support this by promoting the mask to i8 and truncating it, but
for now I want to prevent the crash.

Fixes PR56007.

[craig.topper]

Use getVectorElementType() instead of getScalarType().

[reames]

LGTM

Minor comments:

• "promote to i1" - I think you meant i8.
• Is this a broader problem for other types? e.g. is this a missing legality check on the VGATHER node?

[craig.topper]

In D127681#3579256, @reames wrote:

LGTM

Minor comments:

• "promote to i1" - I think you meant i8.
• Is this a broader problem for other types? e.g. is this a missing legality check on the VGATHER node?

The DAG combine caller already checks isTypeLegal. It's also called by LowerBUILD_VECTOR which should only be called for legal types. I think any legal FP type or non-i1 int type should be ok for the VRGATHER.

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

 // and lower it as a VRGATHER_VX_VL from the source vector.
 static SDValue matchSplatAsGather(SDValue SplatVal, MVT VT, const SDLoc &DL,
                                   SelectionDAG &DAG,
                                   const RISCVSubtarget &Subtarget) {
   if (SplatVal.getOpcode() != ISD::EXTRACT_VECTOR_ELT)
     return SDValue();
   SDValue Vec = SplatVal.getOperand(0);
   // Only perform this optimization on vectors of the same size for simplicity.
-  if (Vec.getValueType() != VT)
+  // Don't perform this optimization for i1 vectors.
+  // FIXME: Support i1 vectors, maybe by promoting to i8?
+  if (Vec.getValueType() != VT || VT.getVectorElementType() == MVT::i1)
     return SDValue();
   SDValue Idx = SplatVal.getOperand(1);
   // The index must be a legal type.
   if (Idx.getValueType() != Subtarget.getXLenVT())
     return SDValue();
 
   MVT ContainerVT = VT;
   if (VT.isFixedLengthVector()) {

llvm/test/CodeGen/RISCV/rvv/vsplats-i1.ll

 ; CHECK-NEXT:    vsetvli a1, zero, e8, m2, ta, mu
 ; CHECK-NEXT:    vmv.v.x v8, a0
 ; CHECK-NEXT:    vmsne.vi v0, v8, 0
 ; CHECK-NEXT:    ret
   %head = insertelement <vscale x 16 x i1> poison, i1 %x, i32 0
   %splat = shufflevector <vscale x 16 x i1> %head, <vscale x 16 x i1> poison, <vscale x 16 x i32> zeroinitializer
   ret <vscale x 16 x i1> %splat
 }
+
+define <vscale x 4 x i1> @splat_idx_nxv4i32(<vscale x 4 x i1> %v, i64 %idx) {
+; CHECK-LABEL: splat_idx_nxv4i32:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetvli a1, zero, e8, mf2, ta, mu
+; CHECK-NEXT:    vmv.v.i v8, 0
+; CHECK-NEXT:    vmerge.vim v8, v8, 1, v0
+; CHECK-NEXT:    vsetivli zero, 1, e8, mf2, ta, mu
+; CHECK-NEXT:    vslidedown.vx v8, v8, a0
+; CHECK-NEXT:    vmv.x.s a0, v8
+; CHECK-NEXT:    andi a0, a0, 1
+; CHECK-NEXT:    vsetvli a1, zero, e8, mf2, ta, mu
+; CHECK-NEXT:    vmv.v.x v8, a0
+; CHECK-NEXT:    vmsne.vi v0, v8, 0
+; CHECK-NEXT:    ret
+  %x = extractelement <vscale x 4 x i1> %v, i64 %idx
+  %ins = insertelement <vscale x 4 x i1> poison, i1 %x, i32 0
+  %splat = shufflevector <vscale x 4 x i1> %ins, <vscale x 4 x i1> poison, <vscale x 4 x i32> zeroinitializer
+  ret <vscale x 4 x i1> %splat
+}
+