Re: [PATCH] x86-64: Compile branred.c with -mprefer-vector-width=128 [BZ #24603]

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Jun 17, 2019 at 12:12 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Jeff Law:
>
> > ISTM that 8, 9, 10 would use the new flag.  11 would issue an error
> > which would trigger a reinvestigation roughly a year from now.
>
> Do you suggest to put in a #warning for GCC 11, so that people can
> configure with --disable-werror and still build with GCC 11?
>
> Given that GCC 11 will probably add other warnings that break the build,
> this proposal isn't entirely unreasonable (even though I generally
> dislike such time bombs).
>

Since there is no issue in source, this requires an artificial warning
purely based on GCC version.   We can place GCC version check in
configure script with explicit -mprefer-vector-width=128 support.

--enable-mprefer-vector-width:

1.  Default.  For GCC 8, 9, 10, use -mprefer-vector-width=128.
For GCC 11 and above, issue a configure error.
2.  Enabled.  No GCC version check, use -mprefer-vector-width=128.
3.  Disabled.  No GCC version check, don't use -mprefer-vector-width=128.

-- 
H.J.