https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110587
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |vmakarov at gcc dot gnu.org
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
Btw, with GCC 13.1 this is already a LRA hog:
LRA non-specific : 3.31 ( 73%) 0.01 ( 9%) 3.33 ( 72%)
3876k ( 3%)
TOTAL : 4.53 0.11 4.65
126M
GCC 8 and before were worse. On trunk:
LRA non-specific : 6.22 ( 69%) 0.02 ( 20%) 6.22 ( 69%)
8922k ( 6%)
LRA hard reg assignment : 1.00 ( 11%) 0.02 ( 20%) 1.02 ( 11%)
0 ( 0%)
TOTAL : 8.97 0.10 9.08
149M
the above is with just -O0.
Profile:
Samples: 37K of event 'cycles:u', Event count (approx.): 49984847870
Overhead Samples Command Shared Object Symbol
51.58% 19087 cc1 cc1 [.] lra_final_code_change
11.10% 4106 cc1 cc1 [.] next_nondebug_insn
7.61% 2879 cc1 cc1 [.] bitmap_set_bit
6.42% 2425 cc1 cc1 [.] find_hard_regno_for_1
2.28% 842 cc1 cc1 [.] bitmap_bit_p
0.99% 365 cc1 cc1 [.]
lra_create_live_ranges_1
it possibly means we now spill more, at -O0 at least. We have a 10%
regression in assembly line count between 13 and trunk.
The main hog in lra_final_code_change is calls to regno_in_use_p and
the loop within that. The BB in this function is _huge_ so the whole
process quickly becomes quadratic. Maybe the whole thing should work
backwards on a BB and this info collected on-the-fly as some "liveness"
problem?
