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

[Vladimir Makarov <vmakarov@redhat.com>]

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.

>
> diff --git a/gcc/lra-lives.cc b/gcc/lra-lives.cc
> index f60e564da82..e4289f13979 100644
> --- a/gcc/lra-lives.cc
> +++ b/gcc/lra-lives.cc
> @@ -250,7 +250,17 @@ update_pseudo_point (int regno, int point, enum point_type type)
>     if (HARD_REGISTER_NUM_P (regno))
>       return;
>   
> -  if (complete_info_p || lra_get_regno_hard_regno (regno) < 0)
> +  /* Pseudos assigned to the FP register could potentially get spilled
> +     to stack slots when lra_update_fp2sp_elimination runs, so keep
> +     their live range info up to date, even if they aren't in memory
> +     right now. */
> +  int hard_regno = lra_get_regno_hard_regno (regno);
> +  HARD_REG_SET set;
> +  CLEAR_HARD_REG_SET(set);
> +  add_to_hard_reg_set (&set, Pmode, HARD_FRAME_POINTER_REGNUM);
> +
> +  if (complete_info_p || hard_regno < 0
> +     || overlaps_hard_reg_set_p (set, PSEUDO_REGNO_MODE (regno), hard_regno))
>       {
>         if (type == DEF_POINT)
>          {
>
>