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 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.

Richard.

> --
> H.J.