[llvm] [IA][RISCV] Add support for vp.load/vp.store with shufflevector (PR #135445)

[Craig Topper via llvm-commits]

================
@@ -644,13 +740,25 @@ static Value *getMask(Value *WideMask, unsigned Factor) {
     }
   }
 
-  if (match(WideMask, m_AllOnes())) {
-    // Scale the vector length of all-ones mask.
-    ElementCount OrigEC =
-        cast<VectorType>(WideMask->getType())->getElementCount();
-    assert(OrigEC.getKnownMinValue() % Factor == 0);
-    return ConstantVector::getSplat(OrigEC.divideCoefficientBy(Factor),
-                                    cast<Constant>(WideMask)->getSplatValue());
+  if (auto *ConstMask = dyn_cast<Constant>(WideMask)) {
+    if (auto *Splat = ConstMask->getSplatValue()) {
+      // All-ones or all-zeros mask.
+      return ConstantVector::getSplat(LeafValueEC, Splat);
+    } else 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 *Ref = ConstMask->getAggregateElement(alignDown(Idx, Factor));
----------------
topperc wrote:

You could avoid the `alignDown` by using `LeafMask`. Something like.

```
Constant *C = ConstMask->getAggregateElement(Idx);
if (LeafMask[Idx / Factor] && LeafMask[Idx / Factor] != C)
  return nullptr;
LeafMask[Idx / Factor] = C;
```

https://github.com/llvm/llvm-project/pull/135445