Re: Shouldn't convert_scalars_to_vector call free_dominance_info?

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

On Fri, Mar 11, 2016 at 3:01 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Mar 11, 2016 at 5:50 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Fri, Mar 11, 2016 at 5:19 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Fri, Mar 11, 2016 at 2:02 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Fri, Mar 11, 2016 at 4:58 AM, Richard Biener
>>>> <richard.guenther@gmail.com> wrote:
>>>>> On Fri, Mar 11, 2016 at 1:47 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>> On Fri, Mar 11, 2016 at 2:06 AM, Richard Biener
>>>>>> <richard.guenther@gmail.com> wrote:
>>>>>>> On Fri, Mar 11, 2016 at 4:10 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>>>> On Thu, Mar 10, 2016 at 7:03 PM, Jeff Law <law@redhat.com> wrote:
>>>>>>>>> On 03/10/2016 08:00 PM, H.J. Lu wrote:
>>>>>>>>>>
>>>>>>>>>> On Thu, Mar 10, 2016 at 1:30 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>> On Thu, Mar 10, 2016 at 1:24 PM, Jeff Law <law@redhat.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> On 03/10/2016 01:18 PM, Richard Biener wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> On March 10, 2016 6:02:58 PM GMT+01:00, "H.J. Lu" <hjl.tools@gmail.com>
>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Thu, Mar 10, 2016 at 6:57 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Thu, Mar 10, 2016 at 5:49 AM, Jakub Jelinek <jakub@redhat.com>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> On Thu, Mar 10, 2016 at 05:43:27AM -0800, H.J. Lu wrote:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> free_dominance_info (CDI_DOMINATORS);
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Since convert_scalars_to_vector may add instructions, dominance
>>>>>>>>>>>>>>>>> info is no longer up to date.
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Adding instructions doesn't change anything on the dominance info,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> just
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> cfg manipulations that don't keep the dominators updated.
>>>>>>>>>>>>>>>> You can try to verify the dominance info at the end of the stv pass,
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> I added
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> verify_dominators (CDI_DOMINATORS);
>>>>>>>>>>>>>>> '
>>>>>>>>>>>>>>> It did trigger assert in my 64-bit STV pass in 64-bit libgcc build:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> /export/gnu/import/git/sources/gcc/libgcc/config/libbid/bid128_fma.c:
>>>>>>>>>>>>>>> In function \u2018add_and_round.constprop\u2019:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> /export/gnu/import/git/sources/gcc/libgcc/config/libbid/bid128_fma.c:629:1:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> error: dominator of 158 should be 107, not 101
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> I will investigate.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Here is the problem:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> 1. I extended the STV pass to 64-bit to convert TI load/store to
>>>>>>>>>>>>>> V1TI load/store to use SSE load/store for 128-bit load/store.
>>>>>>>>>>>>>> 2. The 64-bit STV pass generates settings of CONST0_RTX and
>>>>>>>>>>>>>> CONSTM1_RTX to store 128-bit 0 and -1.
>>>>>>>>>>>>>> 3. I placed the 64-bit STV pass before the CSE pass so that
>>>>>>>>>>>>>> CONST0_RTX and CONSTM1_RTX generated by the STV pass
>>>>>>>>>>>>>> can be CSEed.
>>>>>>>>>>>>>> 4. After settings of CONST0_RTX and CONSTM1_RTX are CSEed,
>>>>>>>>>>>>>> dominance info will be wrong.
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Can't see how cse can ever invalidate dominators.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> cse can simplify jumps which can invalidate dominance information.
>>>>>>>>>>>>
>>>>>>>>>>>> But cse-ing CONST0_RTX and CONSTM1_RTX shouldn't invalidate dominators,
>>>>>>>>>>>> that's just utter nonsense -- ultimately it has to come down to changing
>>>>>>>>>>>> jumps.  ISTM HJ has more digging to do here.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Not just CONST0_RTX and CONSTM1_RTX.  The new STV
>>>>>>>>>>> pass changes mode of SET from TImode to V1TImode which
>>>>>>>>>>> exposes more opportunities to CSE.
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> What I did is equivalent to
>>>>>>>>>>
>>>>>>>>>> diff --git a/gcc/cse.c b/gcc/cse.c
>>>>>>>>>> index 2665d9a..43202a1 100644
>>>>>>>>>> --- a/gcc/cse.c
>>>>>>>>>> +++ b/gcc/cse.c
>>>>>>>>>> @@ -7644,7 +7644,11 @@ public:
>>>>>>>>>>         return optimize > 0 && flag_rerun_cse_after_loop;
>>>>>>>>>>       }
>>>>>>>>>>
>>>>>>>>>> -  virtual unsigned int execute (function *) { return rest_of_handle_cse2
>>>>>>>>>> (); }
>>>>>>>>>> +  virtual unsigned int execute (function *)
>>>>>>>>>> +    {
>>>>>>>>>> +      calculate_dominance_info (CDI_DOMINATORS);
>>>>>>>>>> +      return rest_of_handle_cse2 ();
>>>>>>>>>> +    }
>>>>>>>>>>
>>>>>>>>>>   }; // class pass_cse2
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> which leads to the same ICE:
>>>>>>>>>
>>>>>>>>> But you haven't done the proper analysis to understand why the dominance
>>>>>>>>> relationships have changed.  Nothing of the changes you've outlined in your
>>>>>>>>> messages should invalidate the dominance information.
>>>>>>>>
>>>>>>>> Nothing is changed.  Just calling
>>>>>>>>
>>>>>>>> calculate_dominance_info (CDI_DOMINATORS);
>>>>>>>>
>>>>>>>> before rest_of_handle_cse2 will lead to ICE.
>>>>>>>
>>>>>>> Well, so CSE2 invalidates dominators but fails to free them when necessary.
>>>>>>> Please figure out the CSE transform that invalidates them and free dominators
>>>>>>> there.
>>>>>>
>>>>>> I can give it a try.  But I'd like to first ask since CSE2 never calls
>>>>>> calculate_dominance_info (CDI_DOMINATORS), does it need to
>>>>>> keep dominators valid?
>>>>>
>>>>> If it doesn't free them then yes.
>>>>>
>>>>>> free_dominance_info (CDI_DOMINATORS);
>>>>>>
>>>>>> at beginning will do the job.
>>>>>
>>>>> Of course.  But that may be not always necessary and thus cause extra
>>>>> dominance compute for the next user.
>>>>
>>>> Do we need to both CDI_DOMINATORS and CDI_POST_DOMINATORS
>>>> valid?
>>>
>>> CDI_POST_DOMINATORS is required to be freed by passes.
>>>
>>
>> This works for me.  Should I submit a patch?
>>
>> H.J.
>> ---
>> diff --git a/gcc/cfgrtl.c b/gcc/cfgrtl.c
>> index 62b0596..1307e22 100644
>> --- a/gcc/cfgrtl.c
>> +++ b/gcc/cfgrtl.c
>> @@ -228,7 +228,11 @@ delete_insn_and_edges (rtx_insn *insn)
>>      purge = true;
>>    delete_insn (insn);
>>    if (purge)
>> -    purge_dead_edges (BLOCK_FOR_INSN (insn));
>> +    {
>> +      purge_dead_edges (BLOCK_FOR_INSN (insn));
>> +      if (dom_info_available_p (CDI_DOMINATORS))
>> +  free_dominance_info (CDI_DOMINATORS);
>> +    }
>>  }
>>
>>  /* Unlink a chain of insns between START and FINISH, leaving notes
>
> Or should do it in purge_dead_edges?

If it does purge any edge, yes, and you can free unconditonally
w/o checking if it is available.

Richard.

> --
> H.J.