[clang] [FMV][AArch64] Do not emit ifunc resolver on use. (PR #97761)

[Tomas Matheson via cfe-commits]

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@@ -59,15 +59,22 @@ int bar() {
   return m.goo(1) + foo(1) + foo();
 }
 
+// Example to demonstrate that at the point of use we haven't yet seen the default.
+// At that point a declaration for the unmangled symbol is emitted, which is later
+// replaced by the ifunc symbol (once we have seen the default definition).
+__attribute__((target_version("aes"))) void fmv(void) {}
+void caller(void) { fmv(); }
+__attribute__((target_version("default"))) void fmv(void) {}
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tmatheson-arm wrote:

I think we want to test the observable behaviour, not whatever is happening internally. The test doesn't actually check the internals anyway, besides that it doesn't crash. i.e. I would expect the comment to be something like:
> Test that an ifunc is generated and used when `default` is defined after the first use of the function

If we want to check the other case you mentioned, and `update_cc_test_checks.py` can't generate a test for it automatically, it should still be tested but it will have to be manually written.

https://github.com/llvm/llvm-project/pull/97761