[PATCH] D137899: [Docs] Add Documentation on BOLT Build Configs

[Aiden Grossman via Phabricator via llvm-commits]

aidengrossman added reviewers: beanz, sylvestre.ledru, Amir.
aidengrossman added a comment.

Adds info on using BOLT optimized builds and an example configuration using PGO, ThinLTO, and BOLT for a highly optimized build. Really compelling performance gains were demonstrated at the LLVM US Developer's Meeting, and I wanted to make replication more accessible through better documentation. It also seems like these details are also documented in `clang/cmake/caches/README.txt`. If there's interest for adding documentation there as well, I can open up another patch documenting some of this stuff in more detail (ie enumerating targets added by the BOLT caches as done in the other targets), but the CMake cache files are relatively simple.

These configs are mostly taken from the commit messages where they are implemented, with some slight modifications, particularly removing the `LLVM_ENABLE_LLD` flag in the fully optimized build config in case the user doesn't have LLD installed. I've left the other LLD flags on due to the significantly faster link time due to using LLD.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D137899/new/

https://reviews.llvm.org/D137899