[llvm] [Instrumentation] Mark instrumented calls as implicit (PR #106447)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

> This needs to be tested against actual users of this API before it's merged. The example given in the docs (https://clang.llvm.org/docs/SanitizerCoverage.html)
> 
> ```c
> extern "C" void __sanitizer_cov_trace_pc_guard(uint32_t *guard) {
>   if (!*guard) return;  // Duplicate the guard check.
>   // If you set *guard to 0 this code will not be called again for this edge.
>   // Now you can get the PC and do whatever you want:
>   //   store it somewhere or symbolize it and print right away.
>   // The values of `*guard` are as you set them in
>   // __sanitizer_cov_trace_pc_guard_init and so you can make them consecutive
>   // and use them to dereference an array or a bit vector.
>   void *PC = __builtin_return_address(0);
>   char PcDescr[1024];
>   // This function is a part of the sanitizer run-time.
>   // To use it, link with AddressSanitizer or other sanitizer.
>   __sanitizer_symbolize_pc(PC, "%p %F %L", PcDescr, sizeof(PcDescr));
>   printf("guard: %p %x PC %s\n", guard, *guard, PcDescr);
> }
> ```
> 
> Seems very likely to break (__sanitizer_symbolize_pc will end up finding the line 0 location with the instrumentation sequence in #54873).


I wondering if https://clang.llvm.org/docs/SanitizerCoverage.html#id16 will still work?

https://github.com/llvm/llvm-project/pull/106447