[llvm] [ConstantFolding] Add folding for [de]interleave2, insert and extract (PR #141301)

[Luke Lau via llvm-commits]

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@@ -3734,6 +3738,77 @@ static Constant *ConstantFoldFixedVectorCall(
     }
     return nullptr;
   }
+  case Intrinsic::vector_extract: {
+    auto *Vec = dyn_cast<Constant>(Operands[0]);
+    auto *Idx = dyn_cast<ConstantInt>(Operands[1]);
+    if (!Vec || !Idx)
+      return nullptr;
+
+    unsigned NumElements = FVTy->getNumElements();
+    unsigned VecNumElements =
+        cast<FixedVectorType>(Vec->getType())->getNumElements();
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lukel97 wrote:

You can extract a fixed vector from a scalable vector, do you need to check Vec is fixed too here?

https://github.com/llvm/llvm-project/pull/141301