Re: Moving statements from one BB to other BB.

[Diego Novillo <dnovillo at google dot com>]

On 4/15/08 1:34 PM, Zdenek Dvorak wrote:
> Hi,
>
> > >  > To clarify what Richard means, your assertion that "you have updated
> > >  > SSA information" is false.
> > >  > If you had updated the SSA information, the error would not occur :).
> > >  >
> > >  > How exactly are you updating the ssa information?
> > >  >
> > >  > The general way to update SSA for this case would be:
> > >  >
> > >  > For each statement you have moved:
> > >  >   Call update_stmt (t);
> > >  >
> > >  > Then call update_ssa (TODO_update_ssa) (or instead use
> > >  > rewrite_into_loop_closed_ssa if this is a loop pass).
> > >  >
> > >  > If you do not call update_stmt in this case, update_ssa won't actually
> > >  > do anything.
> > >
> > >  actually, it will not do anything even if he calls update_stmt, as the
> > >  statements that he is moving are already in ssa form, so update_stmt
> > >  will not mark anything for renaming.
> > You are partially right (and right where it matters, that it won't fix
> > the problem)
> > That said, update_stmt on ssa form statements will at least reset the
> > vuse/vdef back to original variables for renaming.
>
> I don't think so; as long as you do not introduce new vops (which you
> should not by just moving the statements), update_stmt is a no-op on
> vops too (unless something has changed since the last time I needed
> this),

Right.  Moving statements in SSA form needs to introduce name->name 
mappings (eg, as is done during loop unrolling).


Diego.