Re: New type-based pool allocator code miscompiled due to aliasing issue?

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Jun 16, 2015 at 11:26 AM, Martin LiÅka <mliska@suse.cz> wrote:
> On 06/15/2015 07:31 PM, Marc Glisse wrote:
>> On Mon, 15 Jun 2015, Martin LiÅka wrote:
>>
>>> Ah, I overlooked that it's not a placement new, but just static casting.
>>> Anyway, if I added:
>>>
>>> cselib_val () {}
>>>
>>> to struct cselib_val and changed the cast to placement new:
>>>  char *ptr = (char *) header;
>>>  return new (ptr) T ();
>>>
>>> I got following compilation error:
>>>
>>> In file included from ../../gcc/alias.c:46:0:
>>> ../../gcc/alloc-pool.h: In instantiation of âT* pool_allocator<T>::allocate() [with T = cselib_val]â:
>>> ../../gcc/cselib.h:51:27:   required from here
>>> ../../gcc/alloc-pool.h:416:23: error: no matching function for call to âcselib_val::operator new(sizetype, char*&)â
>>>   return new (ptr) T ();
>>>                       ^
>>> In file included from ../../gcc/alias.c:47:0:
>>> ../../gcc/cselib.h:49:16: note: candidate: static void* cselib_val::operator new(size_t)
>>>   inline void *operator new (size_t)
>>>                ^
>>> ../../gcc/cselib.h:49:16: note:   candidate expects 1 argument, 2 provided
>>
>> #include <new>
>>
>
> Hi.
>
> <new> header file is not missing (explicit addition of the file does not help).
> Feel free to play with following patch which should fix cselib.h compilation error.

cselib_val overrides the new operator but fails to provide an overload
for the placement new
form.  Fix that and it should work (of course it gets quite awkward
with its 'new' calling
pool.allocate and its placement new doing value-construction then...)

Richard.

> Thanks,
> Martin