[build, lto] Only accept -fuse-linker-plugin if linker supports -plugin (PR lto/46944)

[Richard Guenther]

On Fri, 18 Mar 2011, Rainer Orth wrote:

> Richard Guenther <richard.guenther@gmail.com> writes:
> 
> > It seemed to have disabled linker-plugin support for old binutils
> > with --with-plugin-ld=/usr/local/bin/gold, explicit -fuse-linker-plugin says
> > it is not supported.  The system linker does not have plugin support
> > (nor gold).  /usr/local has gold from binutils 2.20.50.xxx.  So it seems that
> >
> >     # Allow -fuse-linker-plugin to enable plugin support in GNU gold 2.20.
> >     elif test "$ld_is_gold" = yes -a "$ld_vers_major" -eq 2 -a
> > "$ld_vers_minor" -eq 20; then
> >       gcc_cv_lto_plugin=1
> >     fi
> >
> > only allows explicit -fuse-linker-plugin for recent gold but based on checking
> > the system linker version (instead of that of --with-plugin-ld).  I'd say
> > allow explicit -fuse-linker-plugin always if --with-plugin-ld is specified.
> 
> Agreed.  I'll have a look and refrain from installing on 4.6 until this
> is resolved.  I wasn't even aware of --with-plugin-ld, which isn't
> documented in install.texi ;-(  This stuff seems insanely complicated to
> me, though: which user is supposed to deal with such complications?

It's sort of historic ... with plugin support for GNU ld we can probably
drop this flag for 4.7 (eventually I'd even like to enforce the use
of the plugin all the time or disable LTO, just for the sake of reducing
the testing and bugreporting matrix ...).

I just noticed the above with the LTO setup of our SPEC testers
which are using somewhat old system tools.

Thanks,
Richard.