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

On 14/05/2017 01:41, Vinnie Falco via Boost wrote:

On Sat, May 13, 2017 at 5:00 PM, Soul Studios via Boost wrote:

...

My apologies, when my brain saw "expected" it also saw "__builtin_expect" and I immediately assumed an unlikely/likely proposal

Ah, okay thanks.

If you are referring to a cross-platform implementation of __builtin_expect that uses regular C++ then you have my full support, you should propose such a library. As a Visual C++ user I would find that very helpful!

There was a very interesting talk at ACCU (unfortunately in the non-videoed room) by a HFT guy explaining all the ways in which recent GCC versions have bugged __builtin_expect, like inverting the code path you specifically told the compiler was the hot path. GCC devs apparently don't care enough to fix it despite multiple persistent reports, and the feature is now useless on GCC >= 5. The speaker recommended clang, especially very recent clang which is apparently finally being competitive with GCC in generating very tight code. I'd back that up, clang 5.0 is generating much tighter code with Outcome than clang 3.x did, markedly so. 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. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/