[Bug c++/53225] static operator new in multiple inheritance carries incorrect type information for the class

[dimitrisdad at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53225

--- Comment #28 from Thomas W. Lynch <dimitrisdad at gmail dot com> 2012-05-04 22:31:36 UTC ---
I see that example, I understand it, and I appreciate your writing it.

Though we are going a long way from the original "minor bug".  

Had it not been operator new, but another operator or method it would have
correctly assigned the count, as was shown.

The argument made was that operator new was different because "the object did
not exist", however, it is the "type" that determines the offsets (or as you
have artfully pointed out, the 'this' pointers).  The type information is known
at compile time.  The compiler is capable of endowing operator new like other
methods.

It has been pointed out by a couple of people that the C++ standard says that
an object only exists after new finishes, and that is the reason.  However,  an
'object' in that context is an instance, and yes, the instance does not exist
until it is allocated -- but the type information exists before new is called. 
New is not bared from the standard from seeing the type.

So someone else pointed out, that the instance does not exist, so it should not
be assigned to.  That has probably been the best answer I have heard, however,
by convention, allocators do write to an allocated area. In addition, ** the
compiler is not flagging access to the object from inside new ** - it allows it
- in this case  ** it just generates the wrong code ** (and you have artfully
explained why).  This is a minor bug.

So I continue to say it is wrong to close this.  Either the compiler should be
giving at least an error for illegal access to the object, according to the
standard, or the correct type information should be there.  I would interpret
the standard, and convention, to favor the latter.   Currently the compiler
does neither - so there is a minor bug.

This is a faithful summary of the discussion on the topic, where is your
disagreement here?