[clang] [compiler-rt] [libcxxabi] [llvm] Automatic removal of unused standard header (PR #192800)

[via cfe-commits]

serge-sans-paille wrote:

> Why? Please add a motivation to the PR description. For larger changes/long-term efforts/adding CI checks, an RFC would be good.

The goal would be to add a CI step that prevents future regression on that topic. Agreed for the RFC.

> From a compile-time perspective, standard headers are not the problem, because many expensive ones get pulled in almost everywhere through Support/ headers anyway. If anything, we should focus on reducing unneeded includes from LLVM headers, also by using forward declarations where possible. Just focusing on standard headers provides little value, IMO.

Based on that change I can confirm that the amount of preprocessed lines before / after the patch was only shrunk by 24_507 lines, which is mostly negligible compare to the 395_187_372 original ones (only compiling LLVM).

As such the only value of this PR would be to pave the way for automatic regression, if that's a path we want to follow.


https://github.com/llvm/llvm-project/pull/192800