Re: [PATCH] sched1: Fix -fcompare-debug issue in schedule_region [PR105586]

[Surya Kumari Jangala <jskumari@linux.vnet.ibm.com>]

Hi Richard,

On 21/09/22 1:03 pm, Richard Biener wrote:
> On Tue, Sep 20, 2022 at 9:18 AM Surya Kumari Jangala via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Hi Jeff, Richard,
>> Thank you for reviewing the patch!
>> I have committed the patch to the gcc repo.
>> Can I backport this patch to prior versions of gcc, as this is an easy patch to backport and the issue exists in prior versions too?
> 
> It doesn't seem to be a regression so I'd error on the safe side here.

Can you please clarify, should this patch be backported? It is not very clear what "safe side" means here.

Thanks!
Surya

> 
> Richard.
> 
>> Regards,
>> Surya
>>
>>
>> On 31/08/22 9:09 pm, Jeff Law via Gcc-patches wrote:
>>>
>>>
>>> On 8/23/2022 5:49 AM, Surya Kumari Jangala via Gcc-patches wrote:
>>>> sched1: Fix -fcompare-debug issue in schedule_region [PR105586]
>>>>
>>>> In schedule_region(), a basic block that does not contain any real insns
>>>> is not scheduled and the dfa state at the entry of the bb is not copied
>>>> to the fallthru basic block. However a DEBUG insn is treated as a real
>>>> insn, and if a bb contains non-real insns and a DEBUG insn, it's dfa
>>>> state is copied to the fallthru bb. This was resulting in
>>>> -fcompare-debug failure as the incoming dfa state of the fallthru block
>>>> is different with -g. We should always copy the dfa state of a bb to
>>>> it's fallthru bb even if the bb does not contain real insns.
>>>>
>>>> 2022-08-22  Surya Kumari Jangala  <jskumari@linux.ibm.com>
>>>>
>>>> gcc/
>>>>     PR rtl-optimization/105586
>>>>     * sched-rgn.cc (schedule_region): Always copy dfa state to
>>>>     fallthru block.
>>>>
>>>> gcc/testsuite/
>>>>     PR rtl-optimization/105586
>>>>     * gcc.target/powerpc/pr105586.c: New test.
>>> Interesting.    We may have stumbled over this bug internally a little while ago -- not from a compare-debug standpoint, but from a "why isn't the processor state copied to the fallthru block" point of view.   I had it on my to investigate list, but hadn't gotten around to it yet.
>>>
>>> I think there were requests for ChangeLog updates and a function comment for save_state_for_fallthru_edge.  OK with those updates.
>>>
>>> jeff
>>>