[clang] [llvm] [AMDGPU] Add per-kernel kernarg preload count (PR #211059)

[Aaron Ballman via llvm-commits]

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@@ -2525,6 +2525,13 @@ def AMDGPUNumVGPR : InheritableAttr {
   let Subjects = SubjectList<[Function], ErrorDiag, "kernel functions">;
 }
 
+def AMDGPUKernargPreloadCount : InheritableAttr {
+  let Spellings = [Clang<"amdgpu_kernarg_preload_count", 0>];
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AaronBallman wrote:

These comments apply to other amdgpu attributes, so maybe worth addressing in a follow-up.

This means `__attribute__((amdgpu_kernarg_preload_count))` works in both C and C++, but `[[clang::amdgpu_kernarg_preload_count]]` only works in C++ and not C; is there a reason for that? (If the goal is to expose in C++ only, you can set the `LangOpts` for the attribute to do that. e.g., `let LangOpts = [CPlusPlus];`)

Also, should these be limited to just amdgpu targets or do these attributes do something outside of amd gpus? (I would have expected an "attribute ignored" diagnostic in cases where the attribute has no effect.)

https://github.com/llvm/llvm-project/pull/211059