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

[Luis Machado]

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