Re: [PATCH] Tree-level fix for PR 69526

[Jeff Law <law@redhat.com>]

On 09/20/2016 06:31 AM, Robin Dapp wrote:
> Hi,
>
>> I meant to do sth like
>>
>> Index: tree-ssa-propagate.c
>> ===================================================================
>> --- tree-ssa-propagate.c        (revision 240133)
>> +++ tree-ssa-propagate.c        (working copy)
>> @@ -1105,10 +1105,10 @@ substitute_and_fold_dom_walker::before_d
>>        /* Replace real uses in the statement.  */
>>        did_replace |= replace_uses_in (stmt, get_value_fn);
>>
>> -      /* If we made a replacement, fold the statement.  */
>> -      if (did_replace)
>> +      /* Fold the statement.  */
>> +      if (fold_stmt (&i, follow_single_use_edges))
>>         {
>> -         fold_stmt (&i, follow_single_use_edges);
>> +         did_replace = true;
>>           stmt = gsi_stmt (i);
>>         }
>>
>> this would need compile-time cost evaluation (and avoid the tree-vrp.c
>> folding part
>> of your patch).
>
> Using this causes the simplifications to be performed in ccp1 instead of
> fwprop1. I noticed two tests failing that rely on propagation being
> performed in fwprop. Should these be adapted or rather the patch be changed?
ISTM this is an indication that something changed the IL without folding 
prior to ccp & forwprop.  That's not in and of itself bad, but may be 
worth investigating to see if whatever prior pass that made this change 
ought to be adjusted.

That investigation would likely guide you with what to do with the 
testcase.  If you find that the earlier pass should have folded, then 
you fix it and change the testcase to verify the earlier pass folded 
properly.  Else you change the testcase to verify ccp folds the statement.

I'm going to let Richi own the review on this.  Just thought I'd chime 
in on that one topic.
jeff