[llvm] Add EVT::changeVectorElementCount and MVT:changeVectorElementCount (PR #182266)

[Chaitanya Koparkar via llvm-commits]

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@@ -108,6 +108,18 @@ namespace llvm {
       return getVectorVT(Context, EltVT, getVectorElementCount());
     }
 
+    /// Return a VT for a vector type whose attributes match ourselves
+    /// with the exception of the element count that is chosen by the caller.
+    EVT changeVectorElementCount(LLVMContext &Context, ElementCount EC) const {
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ckoparkar wrote:

Oh yeah, good point. The underlying type doesn't change here so the Context should be available in the extended type when it's required. I'll fix this in a follow up.

https://github.com/llvm/llvm-project/pull/182266