Partial training option for PGO

[pascua28]

GCC introduced the -fprofile-partial-training flag which instructs the compiler not to optimize the cold paths for size. With this flag, the cold paths' optimization level will remain the same while optimizing the hot paths even more.

[sunnyflunk]

There is already -fno-profile-sample-accurate which I think is the equivalent behavior.

https://releases.llvm.org/16.0.0/tools/clang/docs/ClangCommandLineReference.html#cmdoption-clang-fprofile-sample-accurate

[HeXis-YS]

Looks like -fno-profile-sample-accurate only works for sample profiles.
For instrumentation profile, you may want to try this.
Specifying --sparse=true when merging profdata removes functions records with 0 execution count, so that these functions can be optimized without profile.