ok for google branch.
David
On Fri, Oct 11, 2013 at 3:17 PM, Rong Xu <x...@google.com> wrote:
> here is the new patch. Note that the hitrate won't change by this
> patch for the case of
> while (__builtin_expect (exp, 0))
>
> Index: predict.c
> ===================================================================
> --- predict.c (revision 203462)
> +++ predict.c (working copy)
> @@ -1951,11 +1951,42 @@ tree_predict_by_opcode (basic_block bb)
> if (val)
> {
> int percent = PARAM_VALUE (BUILTIN_EXPECT_PROBABILITY);
> + int hitrate;
>
> gcc_assert (percent >= 0 && percent <= 100);
> if (integer_zerop (val))
> - percent = 100 - percent;
> - predict_edge (then_edge, PRED_BUILTIN_EXPECT, HITRATE (percent));
> + hitrate = HITRATE (100 - percent);
> + else
> + {
> + /* This handles the cases like
> + while (__builtin_expect (exp, 1)) { ... }
> + W/o builtin_expect, the default HITRATE is 91%.
> + It does not make sense to estimate a lower probability of 90%
> + (current default for builtin_expect) with the annotation.
> + So here, we bump the probability by a small amount. */
> + void **preds = pointer_map_contains (bb_predictions, bb);
> +
> + hitrate = HITRATE (percent);
> + if (preds)
> + {
> + struct edge_prediction *pred;
> + int exit_hitrate = predictor_info [(int)
> PRED_LOOP_EXIT].hitrate;
> +
> + for (pred = (struct edge_prediction *) *preds; pred;
> + pred = pred->ep_next)
> + {
> + if (pred->ep_predictor == PRED_LOOP_EXIT
> + && exit_hitrate > hitrate)
> + {
> + hitrate = exit_hitrate + HITRATE (4);
> + if (hitrate > REG_BR_PROB_BASE)
> + hitrate = REG_BR_PROB_BASE;
> + break;
> + }
> + }
> + }
> + }
> + predict_edge (then_edge, PRED_BUILTIN_EXPECT, hitrate);
> }
> /* Try "pointer heuristic."
> A comparison ptr == 0 is predicted as false.
>
> On Fri, Oct 11, 2013 at 2:45 PM, Rong Xu <x...@google.com> wrote:
>> ok. that makes sense.
>>
>>
>> On Fri, Oct 11, 2013 at 2:41 PM, Xinliang David Li <davi...@google.com>
>> wrote:
>>> Should it be max + some_delta then?
>>>
>>> David
>>>
>>> On Fri, Oct 11, 2013 at 2:32 PM, Rong Xu <x...@google.com> wrote:
>>>> I want to differentiate the cases w/o and w/ builtin.
>>>> If I take the max, they will be the same (91%).
>>>>
>>>> -Rong
>>>>
>>>> On Fri, Oct 11, 2013 at 2:26 PM, Xinliang David Li <davi...@google.com>
>>>> wrote:
>>>>> Why this 'percent += 4' instead of taking the max?
>>>>>
>>>>> David
>>>>>
>>>>> On Fri, Oct 11, 2013 at 2:10 PM, Rong Xu <x...@google.com> wrote:
>>>>>> The trunk version of this patch is submitted for review.
>>>>>>
>>>>>> David: can we have this patch for google/gcc-4_8 branch first?
>>>>>> It tested with regression and google internal benchmarks.
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> -Rong
