ira: Remove soft conflict related code in improve_allocation. [PR117838]HEADtrunkmaster

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 soft conflict related code.

0 files changed, 0 insertions, 0 deletions