https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109237
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Samples: 289K of event 'cycles:u', Event count (approx.): 384226334976
Overhead Samples Command Shared Object Symbol
3.52% 9747 cc1 cc1 [.] bb_is_just_return
#
2.94% 8241 cc1 cc1 [.] df_note_compute
#
2.92% 8085 cc1 cc1 [.] init_alias_analysis
#
2.55% 7035 cc1 cc1 [.]
delete_trivially_dead_insns #
2.28% 6372 cc1 cc1 [.]
contains_no_active_insn_p #
2.16% 6288 cc1 cc1 [.] get_ref_base_and_extent
#
2.02% 5785 cc1 cc1 [.] ggc_set_mark
#
1.55% 4308 cc1 cc1 [.] fast_dce
#
I see that bb_is_just_return is high in the profile and looking at its
implementation I wonder whether on RTL we can scan insns backwards and
stop if the last (real?) insn isn't ANY_RETURN_P ()? Using
FOR_BB_INSNS_REVERSE puts it off the profile completely. Will test a patch.
Similar contains_no_active_insn_p is high up in the profile and it looks
like micro-optimizing it a bit would help. Using NONDEBUG_INSN_P to
guard the flow_active_insn_p call doesn't seem to help (but perf is always
noisy).
