[clang] [Clang] define memory scopes as a builtin enum (PR #185408)

[Sameer Sahasrabuddhe via cfe-commits]

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@@ -874,12 +874,12 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   Builder.defineMacro("__ATOMIC_SEQ_CST", "5");
 
   // Define macros for the clang atomic scopes.
-  Builder.defineMacro("__MEMORY_SCOPE_SYSTEM", "0");
-  Builder.defineMacro("__MEMORY_SCOPE_DEVICE", "1");
-  Builder.defineMacro("__MEMORY_SCOPE_WRKGRP", "2");
-  Builder.defineMacro("__MEMORY_SCOPE_WVFRNT", "3");
-  Builder.defineMacro("__MEMORY_SCOPE_SINGLE", "4");
-  Builder.defineMacro("__MEMORY_SCOPE_CLUSTR", "5");
+  Builder.defineMacro("__MEMORY_SCOPE_SYSTEM", "__memory_scope_system");
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ssahasra wrote:

> Should the same be done for the orderings? 

Orderings are defined by the C11 and C++11 standards, and everyone else just follows the same numbering, so there is no issue there.

> Also is there a reason these were implemented with defineMacro, instead of requiring you to include a builtin header of some sort?

I think #72280 was merely following the pattern set by the orderings. It could have been a header, but having it in the preprocessor means that the Clang scoped extension of the GNU atomics "just works".

https://github.com/llvm/llvm-project/pull/185408