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From: "burnus at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug fortran/42958] Weird temporary array allocation Date: Thu, 04 Feb 2010 19:33:00 -0000 [thread overview] Message-ID: <20100204193256.20990.qmail@sourceware.org> (raw) In-Reply-To: <bug-42958-10053@http.gcc.gnu.org/bugzilla/> ------- Comment #1 from burnus at gcc dot gnu dot org 2010-02-04 19:32 ------- > so, we check if the array-size is empty, ubound - lbound < 0. In that > case we set size to zero. Otherwise we compute it > as (ubound - lbound + 1) *8. > Then we check whether size is negative and error out. > Then we actually allocate max(1,size). The reason for the setting it to zero is that Fortran allows one to allocate a zero-sized array: ALLOCATE ( Array(0:-2) ) The reason for MAX(1, size) is to make ALLOCATE(A(1:0)); if(ALLOCATED(A)) work. (This was added later than "size < 0 ? 0 : size".) Why there is a negative check? Well, I do not know. I also can speculate about a poor man's overflow check, which sometimes indeed works, but often fails. * * * > Why not simply do > size = (ubound - lbound + 1) * 8; > malloc (size); I think that would be the future: With the array descriptor (dope vector) reform, we will have an "allocated" field and thus one can do: descriptor.allocated = true descriptor.data = malloc (max (0,size)) Where "if(allocated(A))" translates into "if(A.allocated)". Actually, maybe one should better use: size = (ubound - lbound + 1) if (size > 0) { descriptor.data = malloc(size) if (descriptor.data == NULL) error ("allocate failed"); } descriptor.allocated = true The "allocated" member of the descriptor is also needed in order to make the following work properly: integer, target :: int integer, pointer :: ptr ptr => int deallocate(ptr, stat=i) ! shall return "i != 0" but not crash Thus, from my side: The negative check should be removed and the simplified version should be applied after the descriptor update. Before the descriptor update (planned for 4.6, breaks ABI) one can use: size = (ubound - lbound + 1) * 8; malloc (max(1,size)); Paul, what do you think? (PS: POSIX Allows "ptr = malloc(0); free(ptr)", where "malloc(0)" returns either NULL or a unique pointer.) -- burnus at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |pault at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42958
next prev parent reply other threads:[~2010-02-04 19:33 UTC|newest] Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-02-04 16:56 [Bug fortran/42958] New: " rguenth at gcc dot gnu dot org 2010-02-04 19:33 ` burnus at gcc dot gnu dot org [this message] 2010-02-05 5:36 ` [Bug fortran/42958] " pault at gcc dot gnu dot org 2010-02-05 9:32 ` rguenther at suse dot de 2010-02-05 14:24 ` rguenth at gcc dot gnu dot org 2010-02-17 20:17 ` jvdelisle at gcc dot gnu dot org 2010-02-20 8:31 ` burnus at gcc dot gnu dot org 2010-03-27 18:55 ` pault at gcc dot gnu dot org 2010-03-27 19:06 ` rguenth at gcc dot gnu dot org 2010-03-27 19:06 ` rguenth at gcc dot gnu dot org 2010-03-27 19:08 ` rguenth at gcc dot gnu dot org 2010-03-27 19:12 ` rguenth at gcc dot gnu dot org 2010-03-28 12:57 ` burnus at gcc dot gnu dot org 2010-03-28 13:05 ` burnus at gcc dot gnu dot org 2010-03-28 13:57 ` burnus at gcc dot gnu dot org 2010-03-28 14:11 ` burnus at gcc dot gnu dot org 2010-03-28 14:45 ` rguenther at suse dot de 2010-04-16 8:18 ` burnus at gcc dot gnu dot org 2010-04-28 14:52 ` rguenth at gcc dot gnu dot org 2010-04-28 15:16 ` amonakov at gcc dot gnu dot org 2010-04-28 15:20 ` jv244 at cam dot ac dot uk 2010-04-28 15:43 ` jb at gcc dot gnu dot org 2010-04-29 10:02 ` paul dot richard dot thomas at gmail dot com 2010-04-29 13:19 ` jakub at gcc dot gnu dot org 2010-04-29 19:09 ` tkoenig at gcc dot gnu dot org
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