LRA for avr: Maintain live range info for pseudos assigned to FP?

[Georg-Johann Lay]

Am 20.11.23 um 08:14 schrieb SenthilKumar.Selvaraj--- via Gcc:
> On Thu, 2023-10-05 at 15:33 -0400, Vladimir Makarov wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>
>> On 9/7/23 07:21, SenthilKumar.Selvaraj@microchip.com wrote:
>>> Hi,
>>>
>>>     One more execution failure for the avr target, this time from
>>>     gcc.c-torture/execute/bitfld-3.c.
>>>
>>>     Steps to reproduce
>>>
>>>     Enable LRA in avr.cc by removing TARGET_LRA_P hook, build with
>>>
>>> $  make all-host && make install-host
>>>
>>>     and then
>>>
>>> $ avr-gcc gcc/testsuite/gcc.c-torture/execute/bitfld-3.c -S -Os -mmcu=avr51 -fdump-rtl-all
>>>
>>>     When lra_update_fp2sp_elimination runs and pseudos assigned to the
>>>     FP have to be spilled to stack slots, they sometimes end up in a
>>>     slot that already has a reg with an overlapping live range.  This is
>>>     because lra_reg_info[regno].live_ranges is NULL for such spilled
>>>     pseudos, and therefore when assign_stack_slot_num_and_sort_pseduos
>>>     checks if lra_intersected_live_ranges_p, it always returns false.
>>>
>>>     In the below reload dump, all the pseudos assigned to FP get
>>>     allocated to slot 0. The live ranges for some of them (r1241 for
>>>     e.g.) conflicts with r603 that was originally assigned to slot 0,
>>>     but they still end up in the same slot, causing the execution failure.
>>>
>> Sorry for the delay with the answer, Senthil.  Avr is unusual target and
>> needs some changes in LRA but the changes improves LRA portability.  So
>> thank you for your work on porting LRA to AVR.
>>
>> The patch is ok for me.  The only comment is that making calculation of
>> the set only once would be nice. Live range calculation in LRA can take
>> a lot of time, code of update_pseudo_point is hot and the worst the set
>> will be really used rarely but it is calculated every time.
>>
>> You can commit the current patch and I'll do it by myself or, if you
>> want, you can modify the patch by yourself and submit it for review and
>> I'll review as soon as possible.  Either way works for me.
> 
> Apologies for the extreme delay in responding - had to sort out some medical issues.
> 
> Is it ok if I commit the patch now? I have one more patch in ira.cc, after
> which I'm hoping the regression results would be good enough to switch the
> avr target to LRA.
> 
> Regards
> Senthil

I have two questions:

1) Is there a command line option to switch back to IRA?

2) Will the X register be used for memory accesses? I am asking because
as far as I understand, there is no replacement for 
LEGITIMIZE_RELOAD_ADDRESS.

Regards,

Johann