[PATCH] D121992: [Clang] [Driver] Add option to set alternative toolchain path

Thu Mar 31 00:06:58 PDT 2022

MaskRay added a comment.

To add more why I think the current semantics may need more discussion before we quickly commit to such a driver option:

- interaction with --dyld-prefix: --sysroot does not affect the fallback --dyld-prefix. It seems even less appropriate for --overlay-platform-toolchain to affect the fallback --dyld-prefix.

If you intend to overlay ld.so, you'll necessarily overlay libc, then --sysroot seems just unneeded at all.

- interaction with --gcc-toolchain: I am a bit unclear we still want the tricky GCC installation detection after --overlay-platform-toolchain is specified. Do you propose that both will add include and library search paths?
- -B: in gcc, when -B prefix specifies a directory, GCC adds $prefix/include to the include search directory. Clang does not do this right now. I think adding it may be an alternative approach to introducing the new option.

The currently picked rules may be suitable for https://github.com/advancetoolchain/advance-toolchain, but could be arbitrary for many other use cases.
Have you considered putting some options into a configuration file <https://clang.llvm.org/docs/UsersManual.html#configuration-files> and using `--config`?

I understand that you probably have some short-term goal to make somethings done, but as I mentioned, there might be some process issue here.
This significant new feature very quickly landed without other driver folks possibly had a chance to chime in.
(FWIW I decided to subscribe all `clang/lib/Driver` patches since I care about this area.)
I very rarely do this but I think it is probably cleaner to revert this patch and discuss it more carefully. I am happy to help you achieve your goal. It's possible that we may still need a driver option.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D121992/new/

https://reviews.llvm.org/D121992