[clang] [Clang][AMDGPU] Stop defaulting to `one-as` for all atomic scopes (PR #120095)

[Dhruva Chakrabarti via cfe-commits]

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@@ -537,7 +537,11 @@ AMDGPUTargetCodeGenInfo::getLLVMSyncScopeID(const LangOptions &LangOpts,
     break;
   }
 
-  if (Ordering != llvm::AtomicOrdering::SequentiallyConsistent) {
+  // OpenCL assumes by default that atomic scopes are per-address space for
+  // non-sequentially consistent operations.
+  if (Scope >= SyncScope::OpenCLWorkGroup &&
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dhruvachak wrote:

Can you explain which scopes will generate the one-as versions with this change? I don't know which ones are in that range: agent, workgroup, wavefront, singlethread are the possible candidates. 

I also don't understand why the one-as should be generated for a specific range of scopes. How do we know that will not lead to mis-compilation?

https://github.com/llvm/llvm-project/pull/120095