[Bug target/53513] SH Target: Add support for fschg and fpchg insns

["chrbr at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53513

--- Comment #11 from chrbr at gcc dot gnu.org ---
(In reply to Oleg Endo from comment #10)
> (In reply to Kazumoto Kojima from comment #9)
> > Although it seems that (1)-(5) in #3 are interesting points, they
> > are almost optimizations.  
> 
> Yep.  Those are not necessary to get the functionality (of not using
> __fpscr_values).
> 
> > I guess that programs with frequent FP
> > mode switchings are simply rare in real world and would be a bit
> > special or even pathological in the first place.
> > I like the idea of mode switching without __fpscr_values even if it
> > requires more instructions on SH4.  Now SH4 is a fairy old core and
> > is not for heavy FP computations anyway.  I think that it won't impact
> > the real working set.
> > It looks to me that Christian's patch is the way to go.
> 
> Yep.  However, when the patch was proposed there were some objections
> regarding the modifications in lcm.c (if I'm not mistaken).  We could try
> again.

there were neither followup nor objections to the last version. I'll post
again, the time to cross-check with epiphany or x96. 

> 
> The reason why I brought up (1)-(5) in #3 was that if one of them is
> eventually implemented (e.g. reorder calculation insns) the changes to lcm.c
> might not be required and could be avoided.  Depending on the implementation
> of such optimization, the mode switch information might have to be
> obtained/maintained in a different way.  However, I at the moment I have no
> concrete ideas/plans.  If Christian's patch is accepted, that's cool, too.

Implementing in LCM can also be a base to expose the architectural mode
flipping extension with other ports (MMX was suggested I think)