[PATCH] D104129: [CSSPGO] Report zero-count probe in profile instead of dangling probes.

Wed Jun 16 10:57:50 PDT 2021

wmi added a comment.

In D104129#2821201 <https://reviews.llvm.org/D104129#2821201>, @wenlei wrote:

> In D104129#2821189 <https://reviews.llvm.org/D104129#2821189>, @hoy wrote:
>
>> In D104129#2821164 <https://reviews.llvm.org/D104129#2821164>, @wenlei wrote:
>>
>>>> Be consistent with dwarf line number based profile.
>>>
>>> This is not accurate, see earlier comments. What i meant was not about "non-probe profile -> dwarf line number profile".
>>>
>>> Otherwise lgtm. Thanks.
>>
>> It should be consistent with non-CS dwarf-based profile. CS dwarf-based profile doesn't have either zero or dangling reported, likely needs a fix. Is that what you meant?
>
> Non-cs dwarf-based profile normally doesn't have zero counts in the profile. Any count below a certain threshold is omitted in the profile to save size. This is the default behavior for our production usage (I believe for google as well). This is why the current change that needs explicit zero is not consistent with afdo.

Google keeps zero counts in the profile. It treats missing lines conservatively and tries to infer their hotness. I vaguely remember there is a flag added to control it.

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https://reviews.llvm.org/D104129