[Libre-soc-bugs] [Bug 1135] add FPSCR and Rounding classes to ieee754fpu

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1135

--- Comment #8 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Jacob Lifshay from comment #7)
> (In reply to Luke Kenneth Casson Leighton from comment #4)
> > * hold off the write to the regfile until it is known
> >   - if the exception has occurred (in which case "CANCEL WRITE" is raised)
> >   - if there is NO CHANCE of the exception occurring
> >     (in which case "DROP SHADOW" is raised)
> 
> I assumed that, i don't know how you got it into your head that I meant we
> should rip that out.

to clarify, this is the plan for much later, for now FPSCR will be
dependency-tracked like any other register.

> 
> according to my plan, fp ops will shadow until they know the sticky bits
> haven't been changed and no fp traps are needed, at which point they drop
> the shadow. if either of those are needed, then standard trap procedures are
> followed, except that setting sticky bits is more like a branch
> misprediction in that it just restarts the following insns instead of a trap
> where it changes MSR and goes to e.g. PC=0x700.

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