Re: [PATCH V3 1/7] df: Add DF_LIVE_SUBREG problem

[Vladimir Makarov <vmakarov@redhat.com>]

On 11/14/23 03:38, Lehua Ding wrote:
>
>
> This is perfectly fine, the code inside the live_subreg problem has a 
> branch that goes through similar logic to live_reg if it finds no 
> subreg inside the program. Then when the optimization level is less 
> than 2, it doesn't track the subreg. By the way, I'd like to ask you 
> if you have certain programs where RA has a big impact on compilation 
> time to offer? Or any suggestions about it?
>
I've analyzed effect of your patches to -O2 compilation time on 
compilation of some old version of combine.c.  The total GCC compilation 
time increased by about 3%. I used x86_64 release mode compiler.  Here 
are my more detail findings:

RA compile time increased by 43%.

54% of this increase is due df_analyze time increase and 38% is due to 
overall ira_color increase (assign_hard_reg execution time increased in 
50 times but still such big increase is 1/3 of overall ira_color increase).

The rest (about 10%) of overall RA increase is mostly LRA increase due 
to lra_create_live_ranges.

To see where 6% GCC compilation time increase on SPEC2017 is spent would 
be more interesting but it needs a lot of time for analysis.