This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Shouldn't convert_scalars_to_vector call free_dominance_info?
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: Richard Biener <richard dot guenther at gmail dot com>, Jakub Jelinek <jakub at redhat dot com>, "Enkovich, Ilya" <ilya dot enkovich at intel dot com>, Uros Bizjak <ubizjak at gmail dot com>, GCC Development <gcc at gcc dot gnu dot org>
- Date: Thu, 10 Mar 2016 13:30:38 -0800
- Subject: Re: Shouldn't convert_scalars_to_vector call free_dominance_info?
- Authentication-results: sourceware.org; auth=none
- References: <CAMe9rOqOcS1rTpvJ1n_g2qiWoyPBbNnGZ-R8A1rwqTBheDHpEg at mail dot gmail dot com> <CAFiYyc3HN6Q7OAihgkU7G6i+NdokMGk_qY3jhDnBBym+sJ7SdA at mail dot gmail dot com> <CAMe9rOpOnPH9Fe4k_XfgAfdWvHiGpeMxm4dbnY2VBG7q7_=EDw at mail dot gmail dot com> <CAFiYyc17WXx94Cj=bbo9Cvjw5NaSxAxw5LViysgv4oDMt=QZRg at mail dot gmail dot com> <CAMe9rOpRiGJpYo_rsP0BmCajyjRnYcFNZK_9S3WSLRxfPKKnXA at mail dot gmail dot com> <CAMe9rOr21CUD5pi--PPPcyPu5fydOfL9V+RCk7_sZJU8j6sKcg at mail dot gmail dot com> <20160310134928 dot GV3017 at tucnak dot redhat dot com> <CAMe9rOourtrcZqRdrbRYDVvEy_Msc+CDRnRxuGvbsAkkjF5_eA at mail dot gmail dot com> <CAMe9rOpPCsXx+r6eg_MikehcHsDaS1uhVTrJiAgQJkpkpdjsSg at mail dot gmail dot com> <C56340A9-1040-42A7-9648-961D582B2519 at gmail dot com> <56E1E626 dot 20109 at redhat dot com>
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.
--
H.J.