[clang] [clang][HIP] Normalize __cdecl on abstract function types to the device default CC on amdgcnspirv (PR #210882)

[via cfe-commits]

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@@ -8349,6 +8349,19 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state, ParsedAttr &attr,
     return true;
 
   const FunctionType *fn = unwrapped.get();
+
+  // On amdgcnspirv, __cdecl on an abstract function type has no device-side
+  // equivalent, so normalize it to the device default CC to match an
+  // unadorned function type. Skip named decls and variadic types.
+  if (CC == CC_C && S.getLangOpts().CUDAIsDevice &&
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schittir wrote:

Could the thiscall virtual-override case from https://github.com/llvm/llvm-project/pull/210882#discussion_r3620440336 get a test too? 

https://github.com/llvm/llvm-project/pull/210882