[GOOGLE] Fix AutoFDO size issue

[Xinliang David Li]

On Thu, Nov 13, 2014 at 2:57 PM, Dehao Chen <dehao@google.com> wrote:
> IIRC, AutoFDO the actual iteration for AutoFDO is mostly <3. But it
> should not harm to set max iter as 10.
>
> On Thu, Nov 13, 2014 at 2:51 PM, Xinliang David Li <davidxl@google.com> wrote:
>> After inline summary is recomputed, the large code growth problem will
>> also be better controlled, right?
>
> For this case, recomputing inline summary does not help because the
> code was bloated in first einline phase.

For recursive inlining, the inline summary for the cloned edges need
to be updated to prevent the growth?

david

>
> Dehao
>
>>
>> David
>>
>> On Thu, Nov 13, 2014 at 2:48 PM, Xinliang David Li <davidxl@google.com> wrote:
>>> Is there a need to have 10 iterations of early inline for autofdo?
>>>
>>> David
>>>
>>> On Thu, Nov 13, 2014 at 2:25 PM, Dehao Chen <dehao@google.com> wrote:
>>>> In AutoFDO, we increase einline iterations. This could lead to
>>>> extensive code bloat if we have recursive calls like:
>>>>
>>>> dtor() {
>>>>   destroy(node);
>>>> }
>>>>
>>>> destroy(node) {
>>>>   destroy(left)
>>>>   destroy(right)
>>>> }
>>>>
>>>> In this case, the size growth will be around 8 which is smaller than
>>>> threshold (11). However, if we allow this to happen for 2 iterations,
>>>> it will expand the size by 1024X. To fix this problem, we want to set
>>>> a much smaller threshold in the AutoFDO case. This is because AutoFDO
>>>> do not not rely on aggressive einline to gain more profile context.
>>>>
>>>> And also, in AutoFDO pass, after we processed a function, we need to
>>>> recompute inline parameters because rebuild_cgraph_edges will zero out
>>>> all inline parameters.
>>>>
>>>> The patch is attached below, bootstrapped and perf test on-going. OK
>>>> for google-4_9?
>>>>
>>>> Thanks,
>>>> Dehao
>>>>
>>>> Index: gcc/auto-profile.c
>>>> ===================================================================
>>>> --- gcc/auto-profile.c (revision 217523)
>>>> +++ gcc/auto-profile.c (working copy)
>>>> @@ -1771,6 +1771,7 @@ auto_profile (void)
>>>>        free_dominance_info (CDI_DOMINATORS);
>>>>        free_dominance_info (CDI_POST_DOMINATORS);
>>>>        rebuild_cgraph_edges ();
>>>> +      compute_inline_parameters (cgraph_get_node
>>>> (current_function_decl), true);
>>>>        pop_cfun ();
>>>>      }
>>>>
>>>> Index: gcc/opts.c
>>>> ===================================================================
>>>> --- gcc/opts.c (revision 217523)
>>>> +++ gcc/opts.c (working copy)
>>>> @@ -1853,6 +1853,12 @@ common_handle_option (struct gcc_options *opts,
>>>>        maybe_set_param_value (
>>>>   PARAM_EARLY_INLINER_MAX_ITERATIONS, 10,
>>>>   opts->x_param_values, opts_set->x_param_values);
>>>> +      maybe_set_param_value (
>>>> +        PARAM_EARLY_INLINING_INSNS, 4,
>>>> +        opts->x_param_values, opts_set->x_param_values);
>>>> +      maybe_set_param_value (
>>>> +        PARAM_EARLY_INLINING_INSNS_COMDAT, 4,
>>>> +        opts->x_param_values, opts_set->x_param_values);
>>>>        value = true;
>>>>      /* No break here - do -fauto-profile processing. */
>>>>      case OPT_fauto_profile: