[clang] [FMV] Emit the resolver along with the default version definition. (PR #84405)

[Alexandros Lamprineas via cfe-commits]

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@@ -84,9 +84,33 @@ int hoo(void) {
   return fp1() + fp2();
 }
 
+// This should generate one target version but no resolver.
+__attribute__((target_version("default"))) int unused_with_forward_default_decl(void);
+__attribute__((target_version("mops"))) int unused_with_forward_default_decl(void) { return 0; }
 
+// This should also generate one target version but no resolver.
+extern int unused_with_implicit_extern_forward_default_decl(void);
+__attribute__((target_version("dotprod")))
+int unused_with_implicit_extern_forward_default_decl(void) { return 0; }
 
+// This should also generate one target version but no resolver.
+__attribute__((target_version("aes"))) int unused_with_default_decl(void) { return 0; }
+__attribute__((target_version("default"))) int unused_with_default_decl(void);
 
+// This should generate two target versions and the resolver.
+__attribute__((target_version("sve"))) int unused_with_default_def(void) { return 0; }
+__attribute__((target_version("default"))) int unused_with_default_def(void) { return 1; }
+
+// This should also generate two target versions and the resolver.
+__attribute__((target_version("fp16"))) int unused_with_implicit_default_def(void) { return 0; }
+int unused_with_implicit_default_def(void) { return 1; }
+
+// This should also generate two target versions and the resolver.
+int unused_with_implicit_forward_default_def(void) { return 0; }
+__attribute__((target_version("lse"))) int unused_with_implicit_forward_default_def(void) { return 1; }
+
+// This should generate a normal function.
+__attribute__((target_version("rdm"))) int unused_without_default(void) { return 0; }
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labrinea wrote:

Anyway, I think this has to do with semantics so it's unrelated to this patch and deserves a separate review if pursued. A quick glance in `clang/lib/Sema/SemaDecl.cpp` suggests that in order to fix it we'd have to remove the early exit in `CheckMultiVersionFirstFunction()`. Let's keep it in mind. 

https://github.com/llvm/llvm-project/pull/84405