> > Setting PARAM_EARLY_INLINING_INSNS to 0 when FDO is enabled should be
> > equivalent to my patch.
>
> Yes. This means it's easy to experiment with other values than zero.
> Basically
> early inlining is supposed to remove abstraction penalty to
>
> a) reduce FDO instrumentation overhead
> b) get more realistic size estimates for the inliner
>
> a) was particularly important back in time for tramp3d, reducing
> profiling runtime
> 1000-fold. b) is generally important.
>
> PARAM_EARLY_INLINING_INSNS is supposed to be a reasonable value to
> get abstraction removed but IIRC we increased it quite a bit to also get more
> early optimization (to get more accurate inliner estimates).
>
> What I am saying is that reducing PARAM_EARLY_INLINING_INSNS makes
> sense for FDO but reducing it to zero is probably a bit much.
>
> Can you do your measurements with values between zero and the current
> default of 14 (wow, 14 ... didn't know it's _that_ high currently ;)).
> What's the
> value that crosses the boundary of diminishing returns regarding to code-size
> improvements for you?
>
> Richard.
Here are the results:
Param Size (GCC5) Time (GCC5) Time (GCC7)
0 44686265 (-8.26%) 58.772s 66.332s
1 45692793 (-6.19%) 40.684s 39.220s
2 45556185 (-6.47%) 35.292s 34.328s
3 46251049 (-5.05%) 28.820s 27.136s
4 47028873 (-3.45%) 24.616s 22.200s
5 47495641 (-2.49%) 20.160s 17.800s
6 47520153 (-2.44%) 16.444s 15.656s
14 48708873 5.620s 5.556s
Param: value of PARAM_EARLY_INLINING_INSNS
Size: code size (.text) of optimized libxul.so
Time: execution time of instrumented tramp3d (-n 25)
To balance between size reduction of optimized binary and speed penalty
of instrumented binary, I set param=6 as baseline and compare:
Param Size score Time score Total
0 3.39 -3.57 -0.18
1 2.54 -2.47 0.07
2 2.65 -2.15 0.50
3 2.07 -1.75 0.32
4 1.41 -1.50 -0.09
5 1.02 -1.23 -0.21
6 1.00 -1.00 0.00
14 0.00 -0.34 -0.34
Therefore, I think param=2 is the best choice.
Is the attached patch OK?
Regards,
Yuan, Pengfei
gcc/ChangeLog
* opts.c (finish_options): Adjust PARAM_EARLY_INLINING_INSNS
when FDO is enabled.
diff --git a/gcc/opts.c b/gcc/opts.c
index 39c190d..b59c700 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -826,8 +826,14 @@ finish_options (struct gcc_options *opts, struct
gcc_options *opts_set,
maybe_set_param_value (PARAM_STACK_FRAME_GROWTH, 40,
opts->x_param_values, opts_set->x_param_values);
}
+ /* Adjust PARAM_EARLY_INLINING_INSNS when FDO is enabled. */
+ if ((opts->x_profile_arc_flag && !opts->x_flag_test_coverage)
+ || (opts->x_flag_branch_probabilities && !opts->x_flag_auto_profile))
+ maybe_set_param_value (PARAM_EARLY_INLINING_INSNS, 2,
+ opts->x_param_values, opts_set->x_param_values);
+
if (opts->x_flag_lto)
{
#ifdef ENABLE_LTO
opts->x_flag_generate_lto = 1;
