Re: [boost] boost::mpl::for_each and value_initialized

Subject: Re: [boost] boost::mpl::for_each and value_initialized
From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2010-01-22 02:01:38

On Wed, 13 Jan 2010 11:11:20 -0600, Niels Dekker - address until  
2010-10-10 <niels_address_until_2010-10-10_at_[hidden]> wrote:

> Peter Foelsche wrote:
>> in boost_1_41_0 there is still an unconditional call to memset in
>> value_initialized()
>
> Fernando Cacciola and I originally added the memset call within  
> value_initialized() for MSVC only, because MSVC's implementation of  
> value-initialization was known to incorrectly leave some bytes  
> uninitialized, in some very relevant use cases.  
> https://svn.boost.org/trac/boost/changeset/39157/trunk/boost/utility/value_init.hpp  
> Thereby we also added extra unit tests, which were passed by MSVC by  
> then, because of the memset. But unfortunately they failed on other  
> compilers (GCC, Borland/Codegear and Sun), because of similar  
> value-initialization issues. That's when we thought it was wise to just  
> have the memset call there for all compilers:  
> https://svn.boost.org/trac/boost/changeset/41942/trunk/boost/utility/value_init.hpp
>
> Do I understand correctly that you want the memset call to be skipped  
> for those compiler versions that have implemented value-initialization  
> entirely correctly? Do you know exactly which compiler versions do  
> implement value-initialization correctly?

Personally, I believe the assumption that by default compilers get
this wrong is incorrect and should be revised. IOW, I think we should
revert to the approach of applying the workaround conditionally for the
specific compilers known to be buggy, and just those -- especially if
we have tests to discover these bugs should they return.

As for the specific compiler versions:

- GCC bugs #30111 and #33916 has been fixed in 4.4 and 4.2.4
   correspondingly [1], [2].

- MSVC bug #100744, despite being marked as "Closed, Won't Fix" [3],
   has actually been fixed in VC9 [4].

- Borland bug #51854 is also reported as being fixed in build
   "12.0.3140.16150" [5]

[1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30111#c10
[2] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916#c12
[3]  
https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=100744
[4]  
https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=335987
[5] http://qc.embarcadero.com/wc/qcmain.aspx?rc=51854

-- 
Aleksey Gurtovoy
MetaCommunications Engineering