[PATCH] add the -mrecip driver flag and process its options

[hfinkel at anl.gov]

In http://reviews.llvm.org/D8989#173978, @spatel wrote:

> In http://reviews.llvm.org/D8989#173974, @hfinkel wrote:
>
> > > > '!' is used as the prefix to indicate disabling (not '-' as you
> >
> > >  > have here).
> >
> > > 
> >
> > > Hmm...how does this ever work as advertised?
> >
> > > 
> >
> > >   $ gcc -O2 -ffast-math -mrecip=!sqrt recip.c
> >
> > >   bash: !sqrt: event not found
> >
> >
> > You need quotes.
>
>
> Right; I'm just questioning whether it's worth following gcc on this interface that requires quotes/escapes in common shells when we have an existing syntax that works without it.


Yes, it is worth it. There is no reason to force users to remember which compiler uses which minor syntactic differences. Users end up quoting lots of stuff, and turning off these reciprocal estimates in modes where they are otherwise on is likely to be rare, so I'm not particularly bothered by the quoting.

That having been said, I'm not enamored with GCC's syntax, plus, as you know, what GCC accepts is actually different depending on the target (x86 vs. PPC, etc.) I think we should either accept this logicak superset with the same syntax as GCC, or just break with GCC completely and use a different option name (maybe -mrecip-est=..., or something like that, which I think is clearer anyway).


http://reviews.llvm.org/D8989

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