[lld] [CGData] LLD for MachO (PR #90166)

[Kyungwoo Lee via llvm-commits]

kyulee-com wrote:

> `-fprofile-generate` supports modifiers like `%p, %h, %m, %t, and %c` to allow generating raw profile filenames based on the run instance. This is especially useful when we want to dump a bunch of raw profiles to a directory.
> 
> https://clang.llvm.org/docs/UsersManual.html#profiling-with-instrumentation
> 
> Do you think we should support something similar given that we can pass a directory to the clang frontend flag in #90304? If we build several binaries, we still want to disambiguate the `.cgdata` files, even if we want to dump them in the same directory. Maybe `%n` could expand to the binary name and `%b` could expand to some build number, which could be anywhere in the path. I'm also not sure if it's better to implement this in Clang or LLVM.

Thank you for the suggestion! I largely copied the Clang flags from IRPGO. Unlike IRPGO, which needs to handle many raw profile data files emitted by runtimes, here we deal with a single codegen data file at build time, similar to how a linker handles a single executable file. Therefore, I think the build system can easily configure this additional flag with the correct path for different binaries. So, I don't think there is a need to support a directory path or these modifiers for simplicity. I'm considering simplifying the Clang flag to avoid this confusion. What do you think?

https://github.com/llvm/llvm-project/pull/90166