Re: [rfc] nopl should not be output on -mtune=i686

[Jakub Jelinek <jakub at redhat dot com>]

On Tue, Feb 08, 2011 at 08:01:17PM +0100, Jan Kratochvil wrote:
> On Tue, 08 Feb 2011 18:23:35 +0100, H.J. Lu wrote:
> > On Tue, Feb 8, 2011 at 9:10 AM, Jan Kratochvil
> > <jan.kratochvil@redhat.com> wrote:
> > > Current binutils HEAD:
> > > -march | -mtune ?| nopl used? ?| after the attached patch: nopl used?
> > > ?- ? ?| ? - ? ? | ? ?no ? ? ? | no
> > > ?i686 ?| -/i686 ?| ? ?no ? ? ? | no
> > > ?- ? ?| ? i686 ?| ? yes = BUG | no
> > > ?core2 | -/core2 | ? yes ? ? ? | yes
> > > ?- ? ?| ? core2 | ? yes = BUG | no
> > >
> > > => Currently suppressing -march now produces more advanced code output, this
> > > ? does not seem correct to me.
> > 
> > By default, x86 assembler assumes that the target processor accepts
> > any instructions.  You can restrict ISA sets by -march and .arch directive.
> 
> Aha, in such case the system build should use some specific -march anyway and
> not just to disable `nopl'.

Not very easily, because lots of packages will contain SSE/SSE2/.../AVX etc.
insns in inline asm etc. and use it conditionally based on used CPU (or with target
attribute switching among functions).  So IMHO requiring that -march= is passed to
gas whenever -mtune= is used doesn't look like a good idea.

	Jakub