[clang] [clang][SYCL] Add sycl_external attribute and restrict emitting device code (PR #140282)

[Tom Honermann via cfe-commits]

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@@ -12937,6 +12937,10 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
   if (D->hasAttr<WeakRefAttr>())
     return false;
 
+  if (LangOpts.SYCLIsDevice && !D->hasAttr<SYCLKernelEntryPointAttr>() &&
+      !D->hasAttr<SYCLExternalAttr>())
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tahonermann wrote:

I mentioned global variables are just one example; we don't want to emit anything that follows the current point of check unless it is explicitly used. I understand the concern, but I think the code is right as is. I suggest we stay with the currently proposed change for now and revisit how to handle this better if a need for more fine-grained selections emerges. Note that DPC++ hasn't demonstrated such a need so far.

I do think adding a comment would be helpful though.

https://github.com/llvm/llvm-project/pull/140282