[Bug target/80782] Configure options to use llvm/clang assembler on Mac

[Bug target/80782] Configure options to use llvm/clang assembler on Mac

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80782

--- Comment #15 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Iain Sandoe from comment #12)
> please could you be more specific about exactly what's not working?
>  - i.e if you're on an older version of the OS.
>  - version of Xcode.

So I'm assuming that this is the part that this is still in WAITING for?

[Bug target/80782] Configure options to use llvm/clang assembler on Mac

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80782

--- Comment #16 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #15)
> (In reply to Iain Sandoe from comment #12)
> > please could you be more specific about exactly what's not working?
> >  - i.e if you're on an older version of the OS.
> >  - version of Xcode.
> 
> So I'm assuming that this is the part that this is still in WAITING for?

I guess so...

cctools 'as' already automatically calls 'clang -cc1as' where the system
supports it and GCC's configuration process detects that this is in force
(where it matters to assembler options).

... so we are already using this on the platform versions for which Apple
defaults to using the LLVM back end (i.e. clang -cc1as) for the assembler.

For some versions of Xcode (before this became the default) it would be
possible modify the configure to add the '-q' flag to force the use of 'clang
-cc1as' instead of the GAS-1.38 based assembler - however, at that point we
would clearly be making it possible to generate instructions that the OS
toolchain was not expecting, so not sure of how useful it would be.

from the original description:

> As a result, GCC generates code that fails to assemble when using optimisation for >any CPU that has support for AVX or newer intrinsics. A pity and often annoying >because the failure can happen only late during a build process.

We should not be trying to generate such instructions on systems that do not
support them - so this implies some different issue is in play.