condition codes, haifa-sched and virtual-stack-vars

[Greg McGary]

law@redhat.com writes:

>  > >         if (REG_P (src)
>  > >             && REGNO (src) >= FIRST_PSEUDO_REGISTER

Oops.  I meant FIRST_VIRTUAL_REGISTER here (it's the same constant though).

>  > >             && REGNO (src) <= LAST_VIRTUAL_REGISTER)
>  > 
>  > I'd take the last condition out.  Consider, for example, that you have
>  > a very large stack frame, such that a pseudo ends up having to be
>  > replaced with (plus (reg SP) (const_int VERY_LARGE_NUMBER))?  Reload
>  > may end up using a scratch register to construct this address, and it
>  > will need an add to do that.  Better be safe and consider any pseudo
>  > reloading risky.
> 
> I had pondered similar solutions, but rejected them as imparing 
> optimization in too many ways.  Some optimizers are more effective
> when moves are "simple".

I also wanted to keep them simple.  I am choosing to live dangerously
and confine this hack to bare virtual regs only.  The target is an
embedded processor without MMU whose entire stack buffers are nowhere
near the 64 Kbyte range of immediate offsets.  Now that I think about
it, your idea about reworking conditional branches to keep the test
and branch together then splitting after reload feels like the cleaner
solution.

Greg