[clang] [clang-tools-extra] [Clang] Use TargetInfo when deciding if an address space is compatible (PR #115777)

[Matt Arsenault via cfe-commits]

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@@ -111,6 +111,18 @@ class LLVM_LIBRARY_VISIBILITY AMDGPUTargetInfo final : public TargetInfo {
     return getPointerWidthV(AddrSpace);
   }
 
+  virtual bool isAddressSpaceSupersetOf(LangAS A, LangAS B) const override {
+    // The flat address space AS(0) is a superset of all the other address
+    // spaces used by the backend target.
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arsenm wrote:

Should reject it, it's not flat addressable. We don't have a magic aperture constant for it and the addrspacecast codegen will fail

https://github.com/llvm/llvm-project/pull/115777