Re: [boost] BOOST_ASSERT and __assume

From: Cory Nelson (phrosty_at_[hidden])
Date: 2005-09-23 14:43:37

On 9/23/05, Marcin Kalicinski <kalita_at_[hidden]> wrote:
> Hi Everybody,
>
> I see there are mixed opinions on use of __assume in BOOST_ASSERT. The chief
> concern is there are people using BOOST_ASSERT in "uncommon" (but still
> valid) ways, such as:
>
> - to show dialog box, but only in debug mode
> - using assert handler to throw during unit testing
> - possibly more
>
> These types of usage would be prohibited if we introduced __assume into
> BOOST_ASSERT, so basically this is a no-no from stability point of view
> (nobody wants his code broken). Btw. the second way can be dealt with with
> disabling __assume if assertion handler is defined.
>
> On the other hand some people (including me) consider __assume to be nice,
> helping optimization and suppressing annoying warnings. I see 3 options:
>
> 1. BOOST_ASSUME
> ===============================================
>
> Put __assume in BOOST_ASSUME and leave BOOST_ASSERT unmodified.
>
> Pros:
> - does not disturb existing code in any way
>
> Cons:
> - no existing code uses it, i.e. all existing libraries would have to be
> modified to take advantage of it; this will probably never happen so most of
> the code will not benefit
> - obscure: most of the people would be confused about it when seeing it for
> the first time

I prefer this way.  I do not think it's a hard concept to understand
and it would be fairly trivial for authors to change their
BOOST_ASSERTs to use it where appropriate.

Using a define to change BOOST_ASSERT limits you to either having it
on or off through the whole file, but BOOST_ASSUME would let you pick
and choose which is best for the situation.

> 2. BOOST_ASSERT + define to enable assume (default: on)
> ===============================================
>
> Pros:
> - does enable assume on all the boost code, some user programs get somewhat
> smaller and faster without any intervention from the programmer
>
> Cons:
> - breaks user code which uses BOOST_ASSERT in "uncommon" way. Would require
> a change in docs that executing BOOST_ASSERT(false) is undefined behavior
> (i.e. different than std::assert)
>
> BOOST_ASSERT + define to enable assume (default: off)
> ===============================================
>
> Pros:
> - does enable assume on all the boost code, some user programs get smaller
> and faster with a simple -D"BOOST_ASSERT_USE_ASSUME" on command line.
>
> Cons:
> - only small number of users will know about that #define, so probably most
> of the code will not benefit.
>
>
> What do you think?
>
> Marcin
>
>
>
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--
Cory Nelson
http://www.int64.org