[Bug optimization/14863] [3.4/3.5 regression] unit-at-a-time causes miscompilation

[rguenth at tat dot physik dot uni-tuebingen dot de]

------- Additional Comments From rguenth at tat dot physik dot uni-tuebingen dot de  2004-04-07 13:26 -------
Subject: Re:  [3.4/3.5 regression] unit-at-a-time
 causes miscompilation

On Wed, 7 Apr 2004, pinskia at gcc dot gnu dot org wrote:

>
> ------- Additional Comments From pinskia at gcc dot gnu dot org  2004-04-07 13:06 -------
> Here is the backtrace I get with the mainline at -O1 -g -funit-at-a-time --param large-function-
> insns=3000:
>
> #0  0x4207af5c in chunk_free () from /lib/i686/libc.so.6
> #1  0x4207acb4 in free () from /lib/i686/libc.so.6
> #2  0x400bf761 in operator delete (ptr=0x4212e0f0)
>     at /home/gates/pinskia/src/gnu/gcc/src/libstdc++-v3/libsupc++/del_op.cc:39
> #3  0x0805faa3 in ~PatchSwapLayout (this=0xbffec080) at pr14863.cc:9943  <-- not right function
> name
> #4  0x080539ff in main (argc=1, argv=0xbffec194) at pr14863.cc:52762
>
>
>
> I think this is related to some pointer :
>  char *tmp = new char[nsize];
>  pBeginNew = reinterpret_cast<T *>(tmp);
>
>
>  char *tmp = reinterpret_cast<char *>(pBegin_m);
>  delete [] tmp;  <--- crashing here
>
> I do not understand why the code is doing this though as you should be just using new T[newsize]
> instead.  The other thing is that you could be over running the buffer which could cause this problem.

Yes, it looks a bit twisted, but I think the purpose of allocating and
deallocating char[] rather than T[] is to allow manual (default)
constructing the objects, or not, by using placement new to the individual
elements.  This has been done for optimization purposes, I think, but I
may be wrong.

Is anything conceptually wrong with the following?

  T *m = reinterpret_cast<T *>(new char[n*sizeof(T)]);
  for (int i=0; i<n; ++i)
    new (&m[i]) T;
  for (int i=0; i<n; ++i)
    m[i].~T();
  delete [] reinterpret_cast<char *>(m);

if yes, there may be problems within the code.  There is bounds checking
code available, so I'll check if we don't override some here.

Richard.

--
Richard Guenther <richard dot guenther at uni-tuebingen dot de>
WWW: http://www.tat.physik.uni-tuebingen.de/~rguenth/


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14863