Re: [PATCH] LTO: fallback to -flto=N if -flto=jobserver does not work.

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Apr 21, 2021 at 3:08 PM Martin Liška <mliska@suse.cz> wrote:
>
> When -flto=jobserver is used and we cannot detect job server, then we can
> still fallbackto -flto=N mode.
>
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>
> Ready to be installed?

I think this behavior needs to be documented - it falls back to a less
conservative (possibly system overloading) mode - which IMHO is
non-obvious and IMHO we shouldn't do.

Richard.

> Thanks,
> Martin
>
> gcc/ChangeLog:
>
>         * lto-wrapper.c (run_gcc): When -flto=jobserver is used, but the
>         makeserver cannot be detected, then use -flto=N fallback.
> ---
>  gcc/lto-wrapper.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
> index 03a5922f8ea..0b626d7c811 100644
> --- a/gcc/lto-wrapper.c
> +++ b/gcc/lto-wrapper.c
> @@ -1585,8 +1585,9 @@ run_gcc (unsigned argc, char *argv[])
>        if (jobserver && jobserver_error != NULL)
>         {
>           warning (0, jobserver_error);
> -         parallel = 0;
> +         /* Fall back to auto parallelism.  */
>           jobserver = 0;
> +         auto_parallel = 1;
>         }
>        else if (!jobserver && jobserver_error == NULL)
>         {
> --
> 2.31.1
>