[clang] [PGO] Add a clang option -fprofile-continuous that enables PGO continuous mode (PR #124353)

[Petr Hosek via cfe-commits]

petrhosek wrote:

> I believe all comments have been addressed. friendly ping. @petrhosek any feedback please?

The high-level comment is that the continuous mode isn't PGO specific, it was actually originally developed primarily for coverage, although it can be used for PGO as well due to the fact that coverage and PGO share the instrumentation and runtime (with the limitation of value profiling not being supported).

I don't think this flag should imply that it's PGO specific by explicitly referring to PGO, rather everywhere in your change where you currently say "PGO", you should say "profiling" (or "instrumentation profiling") to imply that it can be used for both coverage and PGO.

TL;DR `s/PGO/instrumentation profiling/g`

https://github.com/llvm/llvm-project/pull/124353