[PATCH, v2] Recognize a missed usage of a sbfiz instruction

[Luis Machado]

Hi,

On 02/08/2018 10:45 AM, Luis Machado wrote:
> Hi Kyrill,
> 
> On 02/08/2018 09:48 AM, Kyrill Tkachov wrote:
>> Hi Luis,
>>
>> On 06/02/18 15:04, Luis Machado wrote:
>>> Thanks for the feedback Kyrill. I've adjusted the v2 patch based on your
>>> suggestions and re-tested the changes. Everything is still sane.
>>
>> Thanks! This looks pretty good to me.
>>
>>> Since this is ARM-specific and fairly specific, i wonder if it would be
>>> reasonable to consider it for inclusion at the current stage.
>>
>> It is true that the target maintainers can choose to take
>> such patches at any stage. However, any patch at this stage increases
>> the risk of regressions being introduced and these regressions
>> can come bite us in ways that are very hard to anticipate.
>>
>> Have a look at some of the bugs in bugzilla (or a quick scan of the 
>> gcc-bugs list)
>> for examples of the ways that things can go wrong with any of the 
>> myriad of GCC components
>> and the unexpected ways in which they can interact.
>>
>> For example, I am now working on what I initially thought was a 
>> one-liner fix for
>> PR 84164 but it has expanded into a 3-patch series with a midend 
>> component and
>> target-specific changes for 2 ports.
>>
>> These issues are very hard to catch during review and normal testing, 
>> and can sometimes take months of deep testing by
>> fuzzing and massive codebase rebuilds to expose, so the closer the 
>> commit is to a release
>> the higher the risk is that an obscure edge case will be unnoticed and 
>> unfixed in the release.
>>
>> So the priority at this stage is to minimise the risk of destabilising 
>> the codebase,
>> as opposed to taking in new features and desirable performance 
>> improvements (like your patch!)
>>
>> That is the rationale for delaying committing such changes until the 
>> start
>> of GCC 9 development. But again, this is up to the aarch64 maintainers.
>> I'm sure the patch will be a perfectly fine and desirable commit for 
>> GCC 9.
>> This is just my perspective as maintainer of the arm port.
> 
> Thanks. Your explanation makes the situation pretty clear and it sounds 
> very reasonable. I'll put the patch on hold until development is open 
> again.
> 
> Regards,
> Luis

With GCC 9 development open, i take it this patch is worth considering 
again?

Thanks,
Luis