[llvm] [IA] Recognize repeated masks which come from shuffle vectors (PR #150285)

[Luke Lau via llvm-commits]

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@@ -587,6 +587,26 @@ static Value *getMask(Value *WideMask, unsigned Factor,
     }
   }
 
+  if (auto *SVI = dyn_cast<ShuffleVectorInst>(WideMask)) {
+    // Check that the shuffle mask is: a) an interleave, b) all of the same
+    // set of the elements, and c) contained by the first source.  (c) could
+    // be relaxed if desired.
+    unsigned NumSrcElts =
+        cast<FixedVectorType>(SVI->getOperand(1)->getType())->getNumElements();
+    SmallVector<unsigned> StartIndexes;
+    if (ShuffleVectorInst::isInterleaveMask(SVI->getShuffleMask(), Factor,
+                                            NumSrcElts * 2, StartIndexes) &&
+        llvm::all_of(StartIndexes, [](unsigned Start) { return Start == 0; }) &&
+        llvm::all_of(SVI->getShuffleMask(),
+                     [&](int Idx) { return Idx < (int)NumSrcElts; })) {
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lukel97 wrote:

```suggestion
                     [&NumSrcElts](int Idx) { return Idx < (int)NumSrcElts; })) {
```

https://github.com/llvm/llvm-project/pull/150285