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

[Craig Topper via llvm-commits]

================
@@ -3998,20 +3998,28 @@ ConstantFoldStructCall(StringRef Name, Intrinsic::ID IntrinsicID,
     if (!Vec)
       return nullptr;
 
-    unsigned NumElements =
-        cast<VectorType>(Vec->getType())->getElementCount().getKnownMinValue() /
-        2;
+    auto VecTy = cast<VectorType>(Vec->getType());
----------------
topperc wrote:

`auto *VecTy`. Don't hide pointerness with `auto`

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