Re: [boost] BOOST_ASSERT and __assume on MSVC

From: Felipe Magno de Almeida (felipe.m.almeida_at_[hidden])
Date: 2005-09-14 23:15:58

On 9/15/05, Simon Buchan <simon_at_[hidden]> wrote:
> Marcin Kalicinski wrote:
> > Hi All,
> >
> > Have you considered modifying BOOST_ASSERT to use __assume on MSVC?
> >
> > Briefly speaking __assume(expr) is a hint for optimizer that 'expr'
> > evaluates to nonzero. It can help optimize the code. Standalone use of
> > __assume is not recommended because compiler does not check if the
> > assumption is correct, and if it isn't the program is ill formed. But it
> > fits perfectly in ASSERT macro. This way putting many ASSERTs will not only
> > help to verify the code - it will also help the optimizer. Wow!
> <snip>
> I don't get it, isn't the point of assert that it DOES check them? Or
> did you mean something like GCC's __builtin_expect?
> http://gcc.gnu.org/onlinedocs/gcc-4.0.1/gcc/Other-Builtins.html#index-g_t_005f_005fbuiltin_005fexpect-2279

For what I know, the point of assert is that it checks in the debug
build. But has no cost in the release builds. In this case it is even
possible to optimize.

I think this __assume is different from GCC's __builtin_expect because
it still believes it will happens, but the __assume will simply assume
that the case is impossible to happen, just like what an assertion
assumes.

-- 
   Felipe Magno de Almeida
Developer from synergy and Computer Science student from State
University of Campinas(UNICAMP).
Unicamp: http://www.ic.unicamp.br
Synergy: http://www.synergy.com.br
"There is no dark side of the moon really. Matter of fact it's all dark."