COND_EXPR lowering patch

[Zdenek Dvorak]

Hello,

>  >The main showstopper seems to be the tree-ssa-dce; after this change
>  >it cannot work in the current form (resp. it could, but since most
>  > of the interesting control flow will then be expressed by explicit
>  > gotos, it would be useless).
> Actually, as I've stated before, I believe the existing tree-ssa-dce
> should continue to work, even after you've lowered COND_EXPRs because
> we mark the parents of an incoming GOTO_EXPR as being necessary.

yes, it will work, but it will be completely useless.  Consider

if (a)
 {
 }
else
 {
 },

written as

if (a)
  goto _then;
else
  goto _else;

_then:
goto _end;

_else:
_end:

as the code works now all statements here including the condition
will be marked as useful.

Zdenek