Reorganizing -flto and -fwhopr command line options

[Richard Guenther]

On Wed, 6 Oct 2010, Jan Hubicka wrote:

> > On Wed, 6 Oct 2010, Andi Kleen wrote:
> > 
> > > Jan Hubicka <hubicka@ucw.cz> writes:
> > > 
> > > > Hi,
> > > > on a second tought, I wold suggest
> > > >  -flto
> > > >    stay what it is, that is non-streaming single process
> > > >  -flto=1
> > > >    same as -flto
> > > >  -flto=n
> > > >    same as -fwhopr=n
> > > >  -flto=jobserv
> > > >    same as -fwhopr=jobserv
> > > 
> > > Maybe it's possible again to auto detect =jobserver, then
> > > the special option could be removed.
> > > 
> > > I was thinking of defaulting to it when the environment
> > > variables are set and the fds they are pointing to are open.
> > 
> > Yes, I think that in the end a plain -flto should autodetect
> > as much as possible, and -flto=xyz should allow to override
> > autodetection.
> Yes, I like that idea too.
> One thing to keep in mind is that -flto produce different code than -fwhopr
> and has different set of bugs.  So if we get auto detection too far, we might run into
> problems of reproducing user's PRs.

We should perform autodetection in the driver so that -v will report
what was autodetected by explicitly passing -flto=xyz.  And we can
always ask the user to reproduce with -flto=xyz (of course LTO bugs
will be very difficult to reduce with a dynamic partitioning if the
bug depends on a specific paritioning ...)

Richard.