[llvm] [RISCV][TTI] Enable masked interleave vectorization (PR #150074)

[Mel Chen via llvm-commits]

================
@@ -979,12 +979,14 @@ InstructionCost RISCVTTIImpl::getInterleavedMemoryOpCost(
     Align Alignment, unsigned AddressSpace, TTI::TargetCostKind CostKind,
     bool UseMaskForCond, bool UseMaskForGaps) const {
 
-  // The interleaved memory access pass will lower interleaved memory ops (i.e
-  // a load and store followed by a specific shuffle) to vlseg/vsseg
-  // intrinsics.
-  if (!UseMaskForCond && !UseMaskForGaps &&
+  auto *VTy = cast<VectorType>(VecTy);
+
+  // The interleaved memory access pass will lower (de)interleave ops combined
+  // with an adjacent appropriate memory to vlseg/vsseg intrinsics.  We
+  // currently only support masking for the scalable path. vlseg/vsseg only
+  // support masking per-iteration (i.e. condition), not per-segment (i.e. gap).
+  if ((VTy->isScalableTy() || !UseMaskForCond) && !UseMaskForGaps &&
----------------
Mel-Chen wrote:

For fixed-length VF, shuffles are used instead of interleave intrinsics.
However, I believe getMask in the InterleavedAccessPass should already handle shuffle mask:
```
  static Value *getMask(Value *WideMask, unsigned Factor,
                        ElementCount LeafValueEC) {
    if (auto *IMI = dyn_cast<IntrinsicInst>(WideMask)) {
    ...
          if (LeafValueEC.isFixed()) {
        unsigned LeafMaskLen = LeafValueEC.getFixedValue();
        SmallVector<Constant *, 8> LeafMask(LeafMaskLen, nullptr);
        // If this is a fixed-length constant mask, each lane / leaf has to
        // use the same mask. This is done by checking if every group with Factor
        // number of elements in the interleaved mask has homogeneous values.
        for (unsigned Idx = 0U; Idx < LeafMaskLen * Factor; ++Idx) {
          Constant *C = ConstMask->getAggregateElement(Idx);
          if (LeafMask[Idx / Factor] && LeafMask[Idx / Factor] != C)
            return nullptr;
          LeafMask[Idx / Factor] = C;
        }

        return ConstantVector::get(LeafMask);
      }
    }

    return nullptr;
  }
```
Fixed-length should be supported.
Therefore, I think doing it as shown in #149981 should be good enough, right?
```suggestion
  if (!UseMaskForGaps && Factor <= TLI->getMaxSupportedInterleaveFactor())
```



https://github.com/llvm/llvm-project/pull/150074