[RISCV] Stop isInterleaveShuffle from producing illegal extract_subvectors.

[craig.topper]

Summary

The definition for ISD::EXTRACT_SUBVECTOR says the index must be
aligned to the known minimum elements of the extracted type. We mostly
got away with this but it turns out there are places that depend on this.

For example, this code in getNode for ISD::EXTRACT_SUBVECTOR

// EXTRACT_SUBVECTOR of CONCAT_VECTOR can be simplified if the pieces of
// the concat have the same type as the extract.
if (N1.getOpcode() == ISD::CONCAT_VECTORS && N1.getNumOperands() > 0 &&
    VT == N1.getOperand(0).getValueType()) {
  unsigned Factor = VT.getVectorMinNumElements();
  return N1.getOperand(N2C->getZExtValue() / Factor);
}

This depends on N2C->getZExtValue() being evenly divisible by Factor.

[craig.topper]

Fix typo in comment

[luke]

LGTM

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

static bool isInterleaveShuffle(ArrayRef<int> Mask, MVT VT, int &EvenSrc,
   // One source should be low half of first vector.
   if (EvenSrc != 0 && OddSrc != 0)
     return false;
 
   // Subvectors will be subtracted from either at the start of the two input
   // vectors, or at the start and middle of the first vector if it's an unary
   // interleave.
   // In both cases, HalfNumElts will be extracted.
-  // So make sure that EvenSrc/OddSrc are within range.
+  // We need to ensure that the extract indices are 0 or HalfNumElts otherwise
+  // we'll create an illegal extract_subvector.
+  // FIXME: We could support other values using a slidedown first.
   int HalfNumElts = NumElts / 2;
-  return (((EvenSrc % NumElts) + HalfNumElts) <= NumElts) &&
-         (((OddSrc % NumElts) + HalfNumElts) <= NumElts);
+  return ((EvenSrc % HalfNumElts) == 0) && ((OddSrc % HalfNumElts) == 0);
 }
 
 /// Match shuffles that concatenate two vectors, rotate the concatenation,
 /// and then extract the original number of elements from the rotated result.
 /// This is equivalent to vector.splice or X86's PALIGNR instruction. The
 /// returned rotation amount is for a rotate right, where elements move from
 /// higher elements to lower elements. \p LoSrc indicates the first source
 /// vector of the rotate or -1 for undef. \p HiSrc indicates the second vector

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-int-interleave.ll

; V512-NEXT:    ret
   %a = shufflevector <4 x i32> %x, <4 x i32> %y, <4 x i32> <i32 0, i32 6, i32 1, i32 7>
   ret <4 x i32> %a
 }
 
 ; %y should be slid down by 1
 define <4 x i32> @interleave_v4i32_offset_1(<4 x i32> %x, <4 x i32> %y) {
 ; V128-LABEL: interleave_v4i32_offset_1:
 ; V128:       # %bb.0:
-; V128-NEXT:    vsetivli zero, 2, e32, m1, ta, ma
-; V128-NEXT:    vslidedown.vi v10, v9, 1
-; V128-NEXT:    vsetivli zero, 2, e32, mf2, ta, ma
-; V128-NEXT:    vwaddu.vv v9, v8, v10
-; V128-NEXT:    li a0, -1
-; V128-NEXT:    vwmaccu.vx v9, a0, v10
-; V128-NEXT:    vmv1r.v v8, v9
+; V128-NEXT:    vsetivli zero, 4, e32, m1, ta, mu
+; V128-NEXT:    vid.v v10
+; V128-NEXT:    vsrl.vi v11, v10, 1
+; V128-NEXT:    vrgather.vv v10, v8, v11
+; V128-NEXT:    li a0, 10
+; V128-NEXT:    vmv.s.x v0, a0
+; V128-NEXT:    vadd.vi v8, v11, 1
+; V128-NEXT:    vrgather.vv v10, v9, v8, v0.t
+; V128-NEXT:    vmv.v.v v8, v10
 ; V128-NEXT:    ret
 ;
 ; V512-LABEL: interleave_v4i32_offset_1:
 ; V512:       # %bb.0:
-; V512-NEXT:    vsetivli zero, 2, e32, mf2, ta, ma
-; V512-NEXT:    vslidedown.vi v10, v9, 1
-; V512-NEXT:    vwaddu.vv v9, v8, v10
-; V512-NEXT:    li a0, -1
-; V512-NEXT:    vwmaccu.vx v9, a0, v10
-; V512-NEXT:    vmv1r.v v8, v9
+; V512-NEXT:    vsetivli zero, 4, e32, mf2, ta, mu
+; V512-NEXT:    vid.v v10
+; V512-NEXT:    vsrl.vi v11, v10, 1
+; V512-NEXT:    vrgather.vv v10, v8, v11
+; V512-NEXT:    li a0, 10
+; V512-NEXT:    vmv.s.x v0, a0
+; V512-NEXT:    vadd.vi v8, v11, 1
+; V512-NEXT:    vrgather.vv v10, v9, v8, v0.t
+; V512-NEXT:    vmv1r.v v8, v10
 ; V512-NEXT:    ret
   %a = shufflevector <4 x i32> %x, <4 x i32> %y, <4 x i32> <i32 0, i32 5, i32 1, i32 6>
   ret <4 x i32> %a
 }
 
 define <16 x i8> @interleave_v8i8(<8 x i8> %x, <8 x i8> %y) {
 ; V128-LABEL: interleave_v8i8:
 ; V128:       # %bb.0:
; V512-NEXT:    ret
   ret <8 x i32> %a
 }
 
 ; This interleaves the first 2 elements of a vector in opposite order. With
 ; undefs for the remaining elements. We use to miscompile this.
 define <4 x i8> @unary_interleave_10uu_v4i8(<4 x i8> %x) {
 ; V128-LABEL: unary_interleave_10uu_v4i8:
 ; V128:       # %bb.0:
-; V128-NEXT:    vsetivli zero, 2, e8, mf4, ta, ma
-; V128-NEXT:    vslidedown.vi v10, v8, 1
-; V128-NEXT:    vsetivli zero, 2, e8, mf8, ta, ma
-; V128-NEXT:    vwaddu.vv v9, v10, v8
-; V128-NEXT:    li a0, -1
-; V128-NEXT:    vwmaccu.vx v9, a0, v8
+; V128-NEXT:    vsetivli zero, 4, e8, mf4, ta, ma
+; V128-NEXT:    vid.v v9
+; V128-NEXT:    vrsub.vi v10, v9, 1
+; V128-NEXT:    vrgather.vv v9, v8, v10
 ; V128-NEXT:    vmv1r.v v8, v9
 ; V128-NEXT:    ret
 ;
 ; V512-LABEL: unary_interleave_10uu_v4i8:
 ; V512:       # %bb.0:
-; V512-NEXT:    vsetivli zero, 2, e8, mf8, ta, ma
-; V512-NEXT:    vslidedown.vi v10, v8, 1
-; V512-NEXT:    vwaddu.vv v9, v10, v8
-; V512-NEXT:    li a0, -1
-; V512-NEXT:    vwmaccu.vx v9, a0, v8
+; V512-NEXT:    vsetivli zero, 4, e8, mf8, ta, ma
+; V512-NEXT:    vid.v v9
+; V512-NEXT:    vrsub.vi v10, v9, 1
+; V512-NEXT:    vrgather.vv v9, v8, v10
 ; V512-NEXT:    vmv1r.v v8, v9
 ; V512-NEXT:    ret
   %a = shufflevector <4 x i8> %x, <4 x i8> poison, <4 x i32> <i32 1, i32 0, i32 undef, i32 undef>
   ret <4 x i8> %a
 }