Re: aliasing rules and delete operator
Joergen Samson ha scritto:
{ Edits: quoted signature removed. Please don't quote sigs. -mod }
So you are suggesting to write:
inline void myClass::operator delete(void *b)
{
Link* p = new(b) Link;
p->next = head;
head= p;
}
Well, that makes sense, actually. It's more descriptive than the
original code and should probably be as optimal as that, because Link
has a trivial constructor. It would be interesting to know if this code
still triggers the gcc optimizer bug...
Although the code with the placement new seems to be much cleaner than
using a static_cast, the code with the placement new also crashes.
It really seems to me, that the whole problem boils down to the
question, whether the original object "is still an object" when the
delete operator is called.
As far as I understand, this is the situation:
1) while evaluating the delete expression, both the destructor and the
deallocation function are called, in that order (the order is not stated
explicitly in [expr.delete] but I don't think it might be otherwise).
2) the object life-time ends as soon as the destructor call starts
[basic.life]. As Sergei Organov remarked, subobjects may live a little
longer. However, we can be sure that *no* objects are alive in the
memory block once the execution of the destructor is completed.
3) any side-effect of the destructor (such as updating virtual table
pointers, etc.) are part of the execution of the destructor itself.
4) function calls "do not interleave" even if they are declared inline
[intro.execution] (see in particular para 8 and para 17).
If I interpret these points correctly, the deallocation function *can*
assume that no objects are alive in the memory block and that the block
is no longer accessed once the deallocation function is completed.
If in gcc the latter assumption is not satisfied, then it's my opinion
that it's a bug.
Just my two eurocent,
Ganesh
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