[clang] [CIR] Upstream Vector support in elementTypeIfVector (PR #140125)

[Andy Kaylor via cfe-commits]

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@@ -54,10 +54,12 @@ namespace direct {
 namespace {
 /// If the given type is a vector type, return the vector's element type.
 /// Otherwise return the given type unchanged.
-// TODO(cir): Return the vector element type once we have support for vectors
-// instead of the identity type.
 mlir::Type elementTypeIfVector(mlir::Type type) {
-  assert(!cir::MissingFeatures::vectorType());
+  if (auto vecType = mlir::dyn_cast<cir::VectorType>(type))
+    return vecType.getElementType();
+
+  if (auto vecType = mlir::dyn_cast<mlir::VectorType>(type))
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andykaylor wrote:

I've looked at this twice now, and both times I thought these two `if` statements were identical. It took a third look to see that one is checking for `cir::VectorType` and the other is checking for `mlir::VectorType`. Maybe add a comment drawing attention to this fact?

https://github.com/llvm/llvm-project/pull/140125