Re: [vta, vta4.4] merged with trunk and 4.4 @149247, updated VTA patchset

[Richard Guenther <richard dot guenther at gmail dot com>]

On Sun, Jul 12, 2009 at 8:21 AM, Alexandre Oliva<aoliva@redhat.com> wrote:
> On Jul ?7, 2009, Richard Henderson <rth@redhat.com> wrote:
>
>> On 07/07/2009 01:17 PM, Alexandre Oliva wrote:
>>> On Jul ?7, 2009, Richard Guenther<richard.guenther@gmail.com> ?wrote:
>>>> Ok, so I retract the lazy updating theory (I thought it would get rid
>>>> of the move/remove functions). ?Doing lazy updating during checking
>>>> may introduce code generation differences with checking enabled/disabled
>>>> (you shouldn't be changing IL during checking really).
>
>> Definitely no code changes during verification.
>
> So... ?I found out that the verification failures had to do with an
> overconservative decision I'd made in maybe_replace_use_in_debug_stmt():
> to keep a non-current SSA_NAME in place if there wasn't a current
> definition yet.
>
> Turns out that decision was never correct. ?In some such cases, we must
> fallback to the default definition, if there is one. ?In others, we'd
> have had to create a new PHI node in order to have some SSA-valid name
> to refer to.
>
> Problem is, I haven't been able to figure out how to decide at that
> point whether to use a default value, if there is one, or drop the debug
> expression. ?ATM (in the patch I'll post soon) I'm only retaining
> default definitions when they were already there, but I'm pretty sure
> this drops debug info unnecessarily, and I'm a bit concerned it might
> not be right in other cases, although I can't think of any example.
> Suggestions?
>
>
> Anyhow... ?With this, I could do away with check_and_update_debug_stmt()
> &Co, so now all we have is propagate_*_into_debug_stmts(), called from
> release_ssa_name() and a few other places.
>
> No lazy updating, no invalid SSA, no changes during verification. ?Yay!

Great!  Thanks for continuing to look into these issues.

Richard.