Re: patch to fix PR82353

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

On 10/16/2017 10:38 PM, Vladimir Makarov wrote:
> This is another version of the patch to fix
> 
>     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82353
> 
> The patch was successfully bootstrapped on x86-64 with Go and Ada.
> 
> Committed as rev. 253796.

Hi Vladimir,

AFAIU this bit of the patch makes sure that the flags register show up 
in the bb_livein of the bb in which it's used (and not defined before 
the use), but not in the bb_liveout of the predecessors of that bb.

I wonder if that's a compile-speed optimization, or an oversight.

[ I ran into a similar problem for target gcn here (
   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83327 ) with the
   spill_class hook. I've posted a tentative fix in that PR, which
   piggybacks on this fix, but needed a few extra bits to make sure that
   inter-bb propagation was done:
- a bit at the end of process_bb_lives to detect the liveness change and
   then set live_change_p which make sure the propagation is run.
- a bit in lra_create_live_ranges_1 to unmask the registers we want to
   propagate in all_hard_regs_bitmap.
]

Thanks,
- Tom

> Index: lra-lives.c
> ===================================================================
> --- lra-lives.c	(revision 253685)
> +++ lra-lives.c	(working copy)
> @@ -220,6 +220,9 @@ lra_intersected_live_ranges_p (lra_live_
>     return false;
>   }
>   
> +/* The corresponding bitmaps of BB currently being processed.  */
> +static bitmap bb_killed_pseudos, bb_gen_pseudos;
> +
>   /* The function processing birth of hard register REGNO.  It updates
>      living hard regs, START_LIVING, and conflict hard regs for living
>      pseudos.  Conflict hard regs for the pic pseudo is not updated if
> @@ -243,6 +246,8 @@ make_hard_regno_born (int regno, bool ch
>   	|| i != REGNO (pic_offset_table_rtx))
>   #endif
>         SET_HARD_REG_BIT (lra_reg_info[i].conflict_hard_regs, regno);
> +  if (fixed_regs[regno])
> +    bitmap_set_bit (bb_gen_pseudos, regno);
>   }
>   
>   /* Process the death of hard register REGNO.  This updates
> @@ -255,6 +260,11 @@ make_hard_regno_dead (int regno)
>       return;
>     sparseset_set_bit (start_dying, regno);
>     CLEAR_HARD_REG_BIT (hard_regs_live, regno);
> +  if (fixed_regs[regno])
> +    {
> +      bitmap_clear_bit (bb_gen_pseudos, regno);
> +      bitmap_set_bit (bb_killed_pseudos, regno);
> +    }
>   }
>   
>   /* Mark pseudo REGNO as living at program point POINT, update conflicting
> @@ -299,9 +309,6 @@ mark_pseudo_dead (int regno, int point)
>       }
>   }
>   
> -/* The corresponding bitmaps of BB currently being processed.  */
> -static bitmap bb_killed_pseudos, bb_gen_pseudos;
> -
>   /* Mark register REGNO (pseudo or hard register) in MODE as live at
>      program point POINT.  Update BB_GEN_PSEUDOS.
>      Return TRUE if the liveness tracking sets were modified, or FALSE
>