Re: [boost] [optional] Strict Aliasing Warnings on Trunk

Subject: Re: [boost] [optional] Strict Aliasing Warnings on Trunk
From: Bo Persson (bop_at_[hidden])
Date: 2009-12-17 12:51:50

Mathias Gaunard wrote:
> Dean Michael Berris wrote:
>> I've recently been seeing this error more and more especially on
>> GCC with -Wall: /home/dean/boost/boost/optional/optional.hpp:407: 
>> warning:
>> dereferencing pointer ‘<anonymous>’ does break strict-aliasing
>>  rules /home/dean/boost/boost/optional/optional.hpp:427: note:
>> initialized from here and:
>>
>>   /home/dean/boost/boost/function/function_base.hpp:321: warning:
>> dereferencing type-punned pointer will break strict-aliasing rules
>>   /home/dean/boost/boost/function/function_base.hpp:325: warning:
>> dereferencing type-punned pointer will break strict-aliasing rules
>>
>> This is on Linux and GCC 4.4.1.
>>
>> I'm not an expert in this regard but is there a way to either
>> silence or avoid these warnings? Anything you want me to try from 
>> my end?
>
> This was discussed in the past, and some people claimed the warning
> was spurious.
>
> I am personally not convinced whether it is spurious or not,
> however.

Using a reinterpret_cast to convert from one pointer type to an 
unrelated type seems to conflict with the rules at the end of chapter 
3 of the standard.

"If a program attempts to access the stored value of an object through 
an lvalue of other than one of the following
types the behavior is undefined: ..."

The gcc 4.4 documentation recommends using a union, instead of a type 
punned pointer or reference.

Bo Persson