[llvm] Remove unused standard header inclusion: <iterator>, <utility>, <type_traits> (PR #167318)

[via llvm-commits]

serge-sans-paille wrote:

On Mon, Nov 10, 2025 at 12:06:20PM -0800, Kazu Hirata wrote:
> @kazutakahirata approved this pull request.
> 
> LGTM. Thanks!
> 
> Before you go, may I ask how you find these unused headers? Run IWYU and just
> takes a subset of its suggestions? I'm asking this because clang-tidy has
> misc-include-cleaner, but it does not remove things from header files.

I have a home-grown, stupid but surprisingly efficient script that performs the
following:

- hard code the list of « symbols » (types, globals, functions etc)
  officially exported by each header.

- grep (...) for those symbols in each source file that includes a particular
  header

- if a source file includes a header but does not reference any symbol, then
  that header can be removed. If it was carrying a transitive dependency, then
  this might break compilation and I fix it manually.

This approach brings some false negative but very few false positive (could be
possible if some symbol name is built by the preprocessor though).

I generally manually review the changes to make sure everything is good.


https://github.com/llvm/llvm-project/pull/167318