Re: [tree-ssa] cfg_remove_useless_stmts

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> > > Can't this be told to tree-ssa-dom.c CSE instead of doing it so late?  Or
> > > are we doing it on both sides? 
> > 
> > The problem is that this fixes up things that are created by un-ssa
> > pass.  Concretely consider
> > 
> > if (s == 0)
> >   s = 1;
> > 
> > This becomes
> > 
> > if (s_1 == 0)
> >   s_2 = 1
> > s_3 = phi (s_2, s_1)
> > 
> > Constant propagation creates
> > 
> > if (s_1 == 0)
> >   ;
> > s_3 = phi (1, 0)
> > 
> > Un-ssa makes
> > 
> > if (s == 0)
> >   s = 1;
> > else
> >  s = 0;
> > 
> > from it.
> 
> I see... no direct ideas how to deal it more generally then.
> > > THis can be executed only for COND_EXPRs where both arms get nullified,
> > > right? This should be cared of by cfg_cleanup unless something is wrong
> > > with it.
> > 
> > Yes it could; no it is not, since cfg_cleanup is not run after un-ssa.
> 
> It would be nice to unify these two somehow.  I will try to look into it
> later.  Some of the issues should be dealt with if we get rid of GOTOs
> completely that should not take that long anyway.

indeed; with the patch to do it I am currently testing all the goto
removal stuff goes away.

Zdenek