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

[Alex MacLean via llvm-commits]

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@@ -146,6 +146,10 @@ class LLVM_ABI TargetTransformInfoImplBase {
 
   virtual unsigned getFlatAddressSpace() const { return -1; }
 
+  virtual unsigned getAddressSpaceJoin(unsigned AS1, unsigned AS2) const {
+    return AS1 == AS2 ? AS1 : getFlatAddressSpace();
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AlexMaclean wrote:

Agreed, I've moved this case to InferAS and added an assert here.

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