Re: A bug in vrp_meet?

[Qing Zhao <qing.zhao@oracle.com>]

Richard,

thanks a lot for your suggested fix. 

I will try it.

Qing
> On Mar 4, 2019, at 5:45 AM, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Fri, Mar 1, 2019 at 10:02 PM Qing Zhao <qing.zhao@oracle.com> wrote:
>> 
>> 
>> On Mar 1, 2019, at 1:25 PM, Richard Biener <richard.guenther@gmail.com> wrote:
>> 
>> On March 1, 2019 6:49:20 PM GMT+01:00, Qing Zhao <qing.zhao@oracle.com> wrote:
>> 
>> Jeff,
>> 
>> thanks a lot for the reply.
>> 
>> this is really helpful.
>> 
>> I double checked the dumped intermediate file for pass “dom3", and
>> located the following for _152:
>> 
>> ****BEFORE the pass “dom3”, there is no _152, the corresponding Block
>> looks like:
>> 
>> <bb 4> [local count: 12992277]:
>> _98 = (int) ufcMSR_52(D);
>> k_105 = (sword) ufcMSR_52(D);
>> i_49 = _98 > 0 ? k_105 : 0;
>> 
>> ***During the pass “doms”,  _152 is generated as following:
>> 
>> Optimizing block #4
>> ….
>> Visiting statement:
>> i_49 = _98 > 0 ? k_105 : 0;
>> Meeting
>> [0, 65535]
>> and
>> [0, 0]
>> to
>> [0, 65535]
>> Intersecting
>> [0, 65535]
>> and
>> [0, 65535]
>> to
>> [0, 65535]
>> Optimizing statement i_49 = _98 > 0 ? k_105 : 0;
>> Replaced 'k_105' with variable '_98'
>> gimple_simplified to _152 = MAX_EXPR <_98, 0>;
>> i_49 = _152;
>> Folded to: i_49 = _152;
>> LKUP STMT i_49 = _152
>> ==== ASGN i_49 = _152
>> 
>> then bb 4 becomes:
>> 
>> <bb 4> [local count: 12992277]:
>> _98 = (int) ufcMSR_52(D);
>> k_105 = _98;
>> _152 = MAX_EXPR <_98, 0>;
>> i_49 = _152;
>> 
>> and all the i_49 are replaced with _152.
>> 
>> However, the value range info for _152 doesnot reflect the one for
>> i_49, it keeps as UNDEFINED.
>> 
>> is this the root problem?
>> 
>> 
>> It looks like DOM fails to visit stmts generated by simplification. Can you open a bug report with a testcase?
>> 
>> 
>> The problem is, It took me quite some time in order to come up with a small and independent testcase for this problem,
>> a little bit change made the error disappear.
>> 
>> do you have any suggestion on this?  or can you give me some hint on how to fix this in DOM?  then I can try the fix on my side?
> 
> I remember running into similar issues in the past where I tried to
> extract temporary nonnull ranges from divisions.
> I have there
> 
> @@ -1436,11 +1436,16 @@ dom_opt_dom_walker::before_dom_children
>   m_avail_exprs_stack->pop_to_marker ();
> 
>   edge taken_edge = NULL;
> -  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> -    {
> -      evrp_range_analyzer.record_ranges_from_stmt (gsi_stmt (gsi), false);
> -      taken_edge = this->optimize_stmt (bb, gsi);
> -    }
> +  gsi = gsi_start_bb (bb);
> +  if (!gsi_end_p (gsi))
> +    while (1)
> +      {
> +       evrp_range_analyzer.record_def_ranges_from_stmt (gsi_stmt (gsi), false);
> +       taken_edge = this->optimize_stmt (bb, &gsi);
> +       if (gsi_end_p (gsi))
> +         break;
> +       evrp_range_analyzer.record_use_ranges_from_stmt (gsi_stmt (gsi));
> +      }
> 
>   /* Now prepare to process dominated blocks.  */
>   record_edge_info (bb);
> 
> OTOH the issue in your case is that fold emits new stmts before gsi but the
> above loop will never look at them.  See tree-ssa-forwprop.c for code how
> to deal with this (setting a pass-local flag on stmts visited and walking back
> to unvisited, newly inserted ones).  The fold_stmt interface could in theory
> also be extended to insert new stmts on a sequence passed to it so the
> caller would be responsible for inserting them into the IL and could then
> more easily revisit them (but that's a bigger task).
> 
> So, does the following help?
> 
> Index: gcc/tree-ssa-dom.c
> ===================================================================
> --- gcc/tree-ssa-dom.c  (revision 269361)
> +++ gcc/tree-ssa-dom.c  (working copy)
> @@ -1482,8 +1482,25 @@ dom_opt_dom_walker::before_dom_children
>   edge taken_edge = NULL;
>   for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
>     {
> +      gimple_stmt_iterator pgsi = gsi;
> +      gsi_prev (&pgsi);
>       evrp_range_analyzer.record_ranges_from_stmt (gsi_stmt (gsi), false);
>       taken_edge = this->optimize_stmt (bb, gsi);
> +      gimple_stmt_iterator npgsi = gsi;
> +      gsi_prev (&npgsi);
> +      /* Walk new stmts eventually inserted by DOM.  gsi_stmt (gsi) itself
> +        while it may be changed should not have gotten a new definition.  */
> +      if (gsi_stmt (pgsi) != gsi_stmt (npgsi))
> +       do
> +         {
> +           if (gsi_end_p (pgsi))
> +             pgsi = gsi_start_bb (bb);
> +           else
> +             gsi_next (&pgsi);
> +           evrp_range_analyzer.record_ranges_from_stmt (gsi_stmt (pgsi),
> +                                                        false);
> +         }
> +       while (gsi_stmt (pgsi) != gsi_stmt (gsi));
>     }
> 
>   /* Now prepare to process dominated blocks.  */
> 
> 
> Richard.
> 
>> Thanks a lot.
>> 
>> Qing
>> 
>> 
>> 
>> Richard.
>> 
>>