[llvm] [IR] Add new CreateVectorInterleave interface and constant fold (PR #150931)

[David Sherwood via llvm-commits]

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@@ -189,6 +189,24 @@ class LLVM_ABI TargetFolder final : public IRBuilderFolder {
     return nullptr;
   }
 
+  Value *FoldVectorInterleave(ArrayRef<Value *> Ops) const override {
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david-arm wrote:

I can't use the pre-existing `FoldBinaryIntrinsic` or `FoldUnaryIntrinsic` functions either because the number of operands is variable, although I'm happy to add a `FoldUnaryIntrinsic`.

https://github.com/llvm/llvm-project/pull/150931