[clang] [clang][CodeGen] Add query for a target's flat address space (PR #95728)

[Alex Voicu via cfe-commits]

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@@ -1764,6 +1764,13 @@ class TargetInfo : public TransferrableTargetInfo,
     return 0;
   }
 
+  /// \returns Target specific flat ptr address space; a flat ptr is a ptr that
+  /// can be casted to / from all other target address spaces. If the target
+  /// exposes no such address space / does not care, we return 0.
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AlexVlx wrote:

There's no such thing as LangAS::Generic, there's LangAS::Default. Default doesn't have to map to something that's actually useful, and it actually does not. There's no actual mechanism to get a flat pointer. And I have no idea what notion spreading you are talking about - this merely maintains the status quo, wherein everybody grabs an AS 0 pointer and hopes for the best. So I have no idea what you are talking about, if I'm honest.

https://github.com/llvm/llvm-project/pull/95728