Re: [boost] [review] **NEXT WEEK** Review of Outcome (starts Fri-19-May)

Subject: Re: [boost] [review] **NEXT WEEK** Review of Outcome (starts Fri-19-May)
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2017-05-15 11:33:07

On 14/05/2017 12:33, Niall Douglas wrote:
>>> But I can see a feature like __builtin_expect that going the way of the
>>> dodo as the compiler vendors really would prefer if you used profile
>>> guided optimisation instead. Passing that sort of micro-info from the
>>> parser to the backend is surely complex to get right.
>>
>> I looked for bug reports about __builtin_expect in gcc's bugzilla, and
>> the only relevant one I found was
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59521 about using it in a
>> switch. Could you back your statement with some links? Otherwise it
>> sounds like FUD (at least the part about ignoring multiple persistent
>> reports).
> 
> It's possible my memory is faulty, but I don't think it was. It was a
> very good talk, basically a long list with extensive microdetail of how
> compiler version quirks get in the way of micro optimisation. Builtin
> expect was but one of many in a long list.
> 
> The presenter, Jason McGuiness, is one of the more colourful regular
> attendees at ACCU and from all my interactions with him to date, I would
> be considering him to not be FUDing. He's presented similar material at
> ACCU London talks and several others.
> 
> His slides for the ACCU talk aren't online yet, so I'm sent him a
> LinkedIn request and I'll ask for a copy. I'll post a link here if I get
> them.

Jason has provided a copy of the ACCU talk slides at
http://research.ma.cx/ACCU_Conference_2017_v1_1.pdf. Lots of graphs and
assembler showing builtin_expect not working right on GCC.

Niall

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