Gentle ping for this patch.
Thanks,
Lili.
> -----Original Message-----
> From: yes <yes>
> Sent: Friday, August 22, 2025 10:56 AM
> To: gcc-patches@gcc.gnu.org
> Cc: vmaka...@redhat.com; rdsandif...@googlemail.com; Cui, Lili
> <lili....@intel.com>
> Subject: [PATCH] ira: Remove the issue code in improve_allocation.
> [PR117838]
>
> From: "Cui, Lili" <lili....@intel.com>
>
> Hi,
>
> This patch aims to remove issue code in improve_allocation that was causing
> expensive allocno overflows.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
>
> Thanks,
> Lili.
>
>
>
> The original intention of this code was to allow more allocnos to share the
> same register, but this led to expensive allocno overflows. Extracted a small
> case (a bit large, see Bugzilla
> PR117838 for details) from 548.exchange2_r to analyze this register allocation
> issue.
>
> Before improve_allocation function:
>
> a537 (cost 1896, reg42)
> a20 (cost 270, reg1)
> a13 (cost 144, spill)
> a551 (cost 70, reg40)
> a5 (cost 43, spill)
> a493 (cost 30, reg42)
> a499 (cost 12, reg40)
>
> ------------------------------
> Dump info in improve_allocation function:
>
> Base:
> Spilling a493r125 for a5r113
> Spilling a573r202 for a5r113
> Spilling a499r248 for a13r106
> Spilling a551r120 for a13r106
> Spilling a20r237 for a551r120
>
> With patch:
> Spilling a499r248 for a13r106
> Spilling a551r120 for a13r106
> Spilling a493r125 for a551r120
> ------------------------------
>
> After assign_hard_reg (at the end of improve_allocation):
>
> Base:
> a537 (cost 1896, reg1)
> a20 (cost 270, spill) -----> This is unreasonable
> a13 (cost 144, reg40)
> a551 (cost 70, reg1)
> a5 (cost 43, reg42)
> a493 (cost 30, spill)
> a499 (cost 12, reg1)
>
> With patch:
> a537 (cost 1896, reg42)
> a20 (cost 270, reg1)
> a13 (cost 144, reg40)
> a551 (cost 70, reg42)
> a5 (cost 43, spill)
> a493 (cost 30, spill)
> a499 (cost 12, reg42)
> -----------------------------
>
> Collected spec2017 performance on Znver3/Graviton4/EMR/SRF for O2 and
> Ofast.
> No performance regression was observed.
>
> FOR multi-copy O2
> SRF: 548.exchange2_r increased by 7.5%, 500.perlbench_r increased by 2.0%.
> EMR: 548.exchange2_r increased by 4.5%, 500.perlbench_r increased by
> 1.7%.
> Graviton4: 548.exchange2_r Increased by 2.2%, 511.povray_r increased by
> 2.8%.
> Znver3 : 500.perlbench_r increased by 2.0%.
>
> gcc/ChangeLog:
>
> PR rtl-optimization/117838
> * ira-color.cc (improve_allocation): Remove the issue code.
> ---
> gcc/ira-color.cc | 41 +++++++++++------------------------------
> 1 file changed, 11 insertions(+), 30 deletions(-)
>
> diff --git a/gcc/ira-color.cc b/gcc/ira-color.cc index
> 4b9296029cc..fa2ea61cadf
> 100644
> --- a/gcc/ira-color.cc
> +++ b/gcc/ira-color.cc
> @@ -3304,8 +3304,6 @@ improve_allocation (void)
> assigning hard register to allocno A even without spilling
> conflicting allocnos. */
> continue;
> - auto_bitmap allocnos_to_spill;
> - HARD_REG_SET soft_conflict_regs = {};
> mode = ALLOCNO_MODE (a);
> nwords = ALLOCNO_NUM_OBJECTS (a);
> /* Process each allocno conflicting with A and update the cost @@ -
> 3331,40 +3329,24 @@ improve_allocation (void)
> ALLOCNO_COLOR_DATA (conflict_a)->temp = check;
> if ((conflict_hregno = ALLOCNO_HARD_REGNO (conflict_a)) < 0)
> continue;
> - auto spill_a = ira_soft_conflict (a, conflict_a);
> - if (spill_a)
> - {
> - if (!bitmap_set_bit (allocnos_to_spill,
> - ALLOCNO_NUM (spill_a)))
> - continue;
> - ira_loop_border_costs border_costs (spill_a);
> - spill_cost = border_costs.spill_inside_loop_cost ();
> - }
> + spill_cost = ALLOCNO_UPDATED_MEMORY_COST (conflict_a);
> + k = (ira_class_hard_reg_index
> + [ALLOCNO_CLASS (conflict_a)][conflict_hregno]);
> + ira_assert (k >= 0);
> + if ((allocno_costs = ALLOCNO_HARD_REG_COSTS (conflict_a))
> + != NULL)
> + spill_cost -= allocno_costs[k];
> else
> - {
> - spill_cost = ALLOCNO_UPDATED_MEMORY_COST
> (conflict_a);
> - k = (ira_class_hard_reg_index
> - [ALLOCNO_CLASS (conflict_a)][conflict_hregno]);
> - ira_assert (k >= 0);
> - if ((allocno_costs = ALLOCNO_HARD_REG_COSTS
> (conflict_a))
> - != NULL)
> - spill_cost -= allocno_costs[k];
> - else
> - spill_cost -= ALLOCNO_UPDATED_CLASS_COST (conflict_a);
> - spill_cost
> - += allocno_copy_cost_saving (conflict_a, conflict_hregno);
> - }
> + spill_cost -= ALLOCNO_UPDATED_CLASS_COST (conflict_a);
> + spill_cost
> + += allocno_copy_cost_saving (conflict_a, conflict_hregno);
> conflict_nregs = hard_regno_nregs (conflict_hregno,
> ALLOCNO_MODE
> (conflict_a));
> auto note_conflict = [&](int r)
> {
> if (check_hard_reg_p (a, r,
> conflicting_regs,
> profitable_hard_regs))
> - {
> - if (spill_a)
> - SET_HARD_REG_BIT (soft_conflict_regs, r);
> - costs[r] += spill_cost;
> - }
> + costs[r] += spill_cost;
> };
> for (r = conflict_hregno;
> r >= 0 && (int) end_hard_regno (mode, r) > conflict_hregno;
> @@ -3396,7 +3378,6 @@ improve_allocation (void)
> by spilling some conflicting allocnos does not improve the
> allocation cost. */
> continue;
> - spill_soft_conflicts (a, allocnos_to_spill, soft_conflict_regs, best);
> nregs = hard_regno_nregs (best, mode);
> /* Now spill conflicting allocnos which contain a hard register
> of A when we assign the best chosen hard register to it. */
> --
> 2.34.1
