Re: Enable SSA at -O0

[Paolo Bonzini <bonzini at gnu dot org>]

Jan Hubicka wrote:
> > > +  /* We need to coalesce all names originating same SSA_NAME_VAR
> > > +     so debug info remains undisturbed.  */
> > > +  if (!optimize)
> > Would it make sense to do this at optimize <= 1?
>
> I don't know. Variable splitting is quite standard technique in register
> allocation.

But, if you mean flag_web, we don't do it unless -funroll-loops or 
-fpeel-loops, on the ground that the splitting we get from out-of-SSA 
should be enough.  So, enabling this kind of coalescing at -O1 would 
indeed prevent the compiler from doing splitting.

> I am not sure how serious we are about debug info quality
> difference in between -O1 and -O2

Some people (especially the AdaCore guys) have been constantly begging 
for better (usable, at least) -O1 debug info, and FWIW I second that.

Paolo