On Thu, 2024-11-07 at 09:50 -0800, Eduard Zingerman wrote:
> Consider dead code elimination problem for program like below:
>
> main:
> 1: r1 = 42
> 2: call <subprogram>;
> 3: exit
>
> subprogram:
> 4: r0 = 1
> 5: if r1 != 42 goto +1
> 6: r0 = 2
> 7: exit;
>
> Here verifier would visit every instruction and thus
> bpf_insn_aux_data->seen flag would be set for both true (7)
> and falltrhough (6) branches of conditional (5).
> Hence opt_hard_wire_dead_code_branches() will not replace
> conditional (5) with unconditional jump.
[...]
Had an off-list discussion with Alexei yesterday,
here are some answers to questions raised:
- The patches #1,2 with opt_hard_wire_dead_code_branches() changes are
not necessary for dynptr_slice kfunc inlining / branch removal.
I will drop these patches and adjust test cases.
- Did some measurements for dynptr_slice call using simple benchmark
from patch #11:
- baseline:
76.167 ± 0.030M/s million calls per second;
- with call inlining, but without branch pruning (only patch #3):
101.198 ± 0.101M/s million calls per second;
- with call inlining and with branch pruning (full patch-set):
116.935 ± 0.142M/s million calls per second.
