[llvm] [llvm-profgen][SPGO] Support profiles with multiple concurrent processes (PR #169353)

[Wei Wang via llvm-commits]

apolloww wrote:

> Thanks for clarifying the PID filtering. I'm curious, what kind of specific use cases have you encountered where filtering by PID is necessary, rather than aggregating samples from all processes of a given binary?

>From the attached issue #164581, it seems the specific use case is when multiple instances of the same binary are executed in parallel (i.e. ./test 1 & ./test 2). Even though I don't see the difference in term of final profile result between this and running them in sequence, adding the extra PID information to the perf script is necessary to support such case.

https://github.com/llvm/llvm-project/pull/169353