Re: [PATCH, PR83327] Fix liveness analysis in lra for spilled-into hard regs

[Tom de Vries <Tom_deVries@mentor.com>]

On 02/26/2018 12:00 PM, Matthew Fortune wrote:
> Tom de Vries <Tom_deVries@mentor.com> writes:
>> On 01/08/2018 05:32 PM, Tom de Vries wrote:
>>> On 12/18/2017 05:57 PM, Vladimir Makarov wrote:
>>>>
>>>>
>>>> On 12/15/2017 06:25 AM, Tom de Vries wrote:
>>>>>
>>>>> Proposed Solution:
>>>>>
>>>>> The patch addresses the problem, by:
>>>>> - marking the hard regs that have been used in lra_spill in
>>>>>    hard_regs_spilled_into
>>>>> - using hard_regs_spilled_into in lra_create_live_ranges to
>>>>>    make sure those registers are marked in the conflict_hard_regs
>>>>>    of pseudos that overlap with the spill register usage
>>>>>
>>>>> [ I've also tried an approach where I didn't use
>>>>> hard_regs_spilled_into, but tried to propagate all hard regs. I
>>>>> figured out that I needed to mask out eliminable_regset.  Also I
>>>>> needed to masked out lra_no_alloc_regs, but that could be due to
>>>>> gcn-specific problems (pointers take 2 hard regs), I'm not yet sure.
>>>>> Anyway, in the submitted patch I tried to avoid these problems and
>>>>> went for the more minimal approach. ]
>>>>>
>>>> Tom, thank you for the detail explanation of the problem and
>>>> solutions you considered.  It helped me a lot.  Your simple solution
>>>> is adequate as the most transformations and allocation are done on
>>>> the 1st LRA subpasses iteration.
>>>>> In order to get the patch accepted for trunk, I think we need:
>>>>> - bootstrap and reg-test on x86_64
>>>>> - build and reg-test on mips (the only primary platform that has the
>>>>>    spill_class hook enabled)
>>>>>
>>>>> Any comments?
>>>>
>>>> The patch looks ok to me.  You can commit it after successful testing
>>>> on x86-64 and mips but I am sure there will be no problems with
>>>> x86-64 as it does not use spill_class currently (actually your patch
>>>> might help to switch it on again for x86-64.  spill_class was quite
>>>> useful for x86-64 performance on Intel processors).
>>>>
>>>
>>> Hi Matthew,
>>>
>>> there's an lra optimization that is currently enabled for MIPS, and
>>> not for any other primary or secondary target.
>>>
>>> This (already approved) patch fixes a bug in that optimization, and
>>> needs to be tested on MIPS.
>>>
>>> Unfortunately, the optimization is only enabled for MIPS16, and we
>>> don't have a current setup to test this.
>>>
>>> Could you help us out here and test this patch for MIPS16 on trunk?
>>
>> Hi Matthew,
>>
>> is this something you can help us out with?
> 
> Hi Tom,
> 
> I've just commented on the bug report that I've set of some builds to try
> and give some assurance. It is far from comprehensive but it is as good as
> the normal testing I do for MIPS16.
> 

Hi Matthew,

Awesome, thanks for the help.

- Tom