[tree-ssa] COND_EXPR lowering preview

[Zdenek Dvorak]

Hello,

> > I don't see the value in having it separate.  All that does is force 
> > another walk over the statements, which seems awful wasteful.  I'd
> > prefer to see this lowering happen during gimplification.
> > 
> We are going to be doing separate lowering pass with EH.  We can
> piggyback all the lowering code in there.
> 
> The reason I tend to prefer this is more stylistic than anything else. 
> The only example I had in mind was code analysis.  The purist in me
> would like to have a clean separation between GIMPLE as an IL and the
> lowering of GIMPLE to benefit our scalar optimizers.  Since we are
> already going to do a separate lowering pass, we could do it there.
> 
> But, as I said before, I'm not that opposed to doing it in the
> gimplifier.  I don't have a strong technical reason now, so I'm happy
> with what the majority thinks it's best.

from "amount of work" point of view, I would slightly prefer a separate
pass too.  With cond_exprs I have somehow managed to place it into
gimplification (although even this was more complicated than I thought),
but for switch_expr lowering, this imho would be quite cumbersome.

Zdenek