Re: [PATCH] ltmain.in: don't suppress output for PIC compilations

[Sam James]

Sam James <sam@gentoo.org> writes:

> I just hit this in a fascinating place.
>
> When working on xz, I set `-Werror=suggest-attribute=returns_nonnull`, and
> the build failed (as I expected it to), but with no visible error from
> the compiler.
>
> There's a mysterious '>/dev/null 2>&1' on the second line where
> liblzma_la-common.o is built without PIC.
>
> With -fPIC, IPA doesn't end up doing attribute discovery. Without it,
> it does. This behaviour is insane and we should patch it out.
>
> Bug: https://bugs.gentoo.org/135865
> Cc: glaubitz@physik.fu-berlin.de
> Signed-off-by: Sam James <sam@gentoo.org>
> ---
> Please consider this kind of a PoC for discussion. This came up on the
> GCC bug tracker the other day which prompted me to post it and get people's
> opinions. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55212#c158.

(Also, if we agree the idea is fine, I'll improve the commit message --
it was just written out of exasperation for a local patchset when I was
debugging something and going mad, sorry!)

>
> libtool assumes that the warning output with vs without -fPIC is going
> to be identical, hence the non-PIC build output should be completely 
> suppressed.
>
> I think this is a premature optimization at best, and it's caused real
> confusion to people. Can we drop it?
>
> If this looks OK, I can check more closely if I need to remove more
> bits.
>
>  build-aux/ltmain.in | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/build-aux/ltmain.in b/build-aux/ltmain.in
> index 63377541..48e89042 100644
> --- a/build-aux/ltmain.in
> +++ b/build-aux/ltmain.in
> @@ -1665,8 +1665,6 @@ compiler."
>       func_append command " -o $obj"
>        fi
>  
> -      # Suppress compiler output if we already did a PIC compilation.
> -      func_append command "$suppress_output"
>        func_show_eval_locale "$command" \
>          '$opt_dry_run || $RM $removelist; exit $EXIT_FAILURE'
>  
>
> base-commit: 22a7e547e9857fc94fe5bc7c921d9a4b49c09f8e