Enable first scheduling pass for SH4

["Sanjiv Kumar Gupta, Noida" <sanjivg at noida dot hcltech dot com>]

> > > On Wed, Sep 03, 2003 at 01:56:26PM +0530, Sanjiv Kumar Gupta,
> > > Noida wrote:
> > > > The overall idea is to keep count of SImode and SFmode regs
> > > required by
> > > > already scheduled insns.
> > >
> > > I don't think this should at all be done via magic hooks in
> > > the sh backend.
> >
> > The heuristics are pretty target specific. Do you think,
> > I should change the generic scheduler for this?
> >
> I think Richard is right.  You could make it more general (register
> pressure calculation and reordering ready queue) because it could be
> profitable for other ports (like arm or sparc)  too.  Then the most of
> code could be in the scheduler itself.  And may be one hook 
> to switch on (off) the heuristic for ports which could have benefit from
this
> heuristic.  If there is no harm from this for all ports, the 
> hook could be removed.

The attached patch makes register pressure calculation for SFmode/SImodes
in generic scheduler. A new target hook is added to use the code. The 
hook lets a target define when insn movement needs to be throttled.
It can see the how many SImode/SFModes regs are in use in current schedule
and returns non-zero, in case, ready_queue is to be reordered based 
on register pressure.More modes might be added later if needed.
In case of SH, r0 needs special consideration. This is accomodated 
in sh_track_register_pressure.

I have tested this for sh. Also bootstraped/regtested on ia64.
Let me know if it helps other targets.

One more point, the change in gcc/flow.c is a workaround I mentioned
in 
 
Regards, 
--sanjiv.

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