Re: [boost] BOOST_ASSERT and __assume on MSVC

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-10-03 16:40:51

Rob Stewart wrote:
> From: Felipe Magno de Almeida <felipe.m.almeida_at_[hidden]>
>> On 10/3/05, Rob Stewart <stewart_at_[hidden]> wrote:
>>>
>>> (Note that __assume(false) is useless, for it is an expression
>>> that the optimizer cannot use to optimize anything.  So, while I
>>> understand that you were trying to simplify things for the
>>> discussion, let's also not lose sight of what is really meant
>>> when writing __assume(false) in the above examples.)
>>
>> I think you're wrong.
>> __assume(false) means that this code will never be executed, and as
>> such isnt useless for the optimizer.
>
> Hmmm.  I guess you're right.  Still, it only means that the code
> following __assume(false) can be elided, not any preceeding code,
> right?

The preceding code can be elided if the compiler can prove that it doesn't 
affect the reachability of __assume(false). ++x can, a function call cannot 
(in general) without whole program optimization.