[llvm] [InferAddressSpaces] Add a TTI hook for address space joins (PR #225161)

[Alex MacLean via llvm-commits]

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@@ -565,6 +565,11 @@ class TargetTransformInfo {
   /// optimize away.
   LLVM_ABI unsigned getFlatAddressSpace() const;
 
+  /// Return the most specific common address space containing AS1 and AS2.
+  /// Pointers from either input space must be convertible to the result with
+  /// addrspacecast.
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AlexMaclean wrote:

Yes, I've updated the comment to include this.

https://github.com/llvm/llvm-project/pull/225161