[Bug libstdc++/29286] [4.0/4.1/4.2/4.3 Regression] placement new does not change the dynamic type as it should

["gdr at cs dot tamu dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #114 from gdr at cs dot tamu dot edu  2007-05-22 18:01 -------
Subject: Re:  [4.0/4.1/4.2/4.3 Regression] placement new does not change the
dynamic type as it should

"mark at codesourcery dot com" <gcc-bugzilla@gcc.gnu.org> writes:

| Subject: Re:  [4.0/4.1/4.2/4.3 Regression] placement
|  new does not change the dynamic type as it should
| 
| gdr at cs dot tamu dot edu wrote:
| > ------- Comment #112 from gdr at cs dot tamu dot edu  2007-05-22 17:46
-------
| > Subject: Re:  [4.0/4.1/4.2/4.3 Regression] placement new does not change
the
| > dynamic type as it should
| > 
| > "mark at codesourcery dot com" <gcc-bugzilla@gcc.gnu.org> writes:
| > 
| > |                         But, I don't think the standard contemplated
| > | these issues in sufficient detail to make it useful in this respect.
| > 
| > The issues has been raised on the -core reflector.
| 
| So that I understand, do you mean that they have been raised in the
| past, and settled, or that you've just raised them now?

I just raised it, mainly because I do not believe your conclusions are
right. 

The type information you can get from write and read  are not just
those appearing lexically in a scope.  In fact, the semantics is defined
in terms of the run time read and write access.  
That is what makes "C a strongly typed and weakly check language" (DMR).

This whole issue does not mean you have to abandon TBAA.  It means you
have be careful in how you use the information gained from TBAA.  In
particular, many conclusions are OK when you have the definition of
the objects at hand.

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29286