On 8/30/21 4:46 AM, Thomas Schwinge wrote:
Hi!
Ping -- we still need to plug the memory leak; see patch attached, and/or
long discussion here:
Thanks for answering my questions. I have no concerns with going
forward with the patch as is. Just a suggestion/request: unless
this patch fixes all the outstanding problems you know of or suspect
in this area (leaks/missing dtor calls) and unless you plan to work
on those in the near future, please open a bug for them with a brain
dump of what you learned. That should save us time when the day
comes to tackle those.
Martin
On 2021-08-16T14:10:00-0600, Martin Sebor wrote:
On 8/16/21 6:44 AM, Thomas Schwinge wrote:
On 2021-08-12T17:15:44-0600, Martin Sebor via Gcc wrote:
On 8/6/21 10:57 AM, Thomas Schwinge wrote:
So I'm trying to do some C++... ;-)
Given:
/* A map from SSA names or var decls to record fields. */
typedef hash_map field_map_t;
/* For each propagation record type, this is a map from SSA names or var
decls
to propagate, to the field in the record type that should be used for
transmission and reception. */
typedef hash_map record_field_map_t;
Thus, that's a 'hash_map>'. (I may do that,
right?) Looking through GCC implementation files, very most of all uses
of 'hash_map' boil down to pointer key ('tree', for example) and
pointer/integer value.
Right. Because most GCC containers rely exclusively on GCC's own
uses for testing, if your use case is novel in some way, chances
are it might not work as intended in all circumstances.
I've wrestled with hash_map a number of times. A use case that's
close to yours (i.e., a non-trivial value type) is in cp/parser.c:
see class_to_loc_map_t.
Indeed, at the time you sent this email, I already had started looking
into that one! (The Fortran test cases that I originally analyzed, which
triggered other cases of non-POD/non-trivial destructor, all didn't
result in a memory leak, because the non-trivial constructor doesn't
actually allocate any resources dynamically -- that's indeed different in
this case here.) ..., and indeed:
(I don't remember if I tested it for leaks
though. It's used to implement -Wmismatched-tags so compiling
a few tests under Valgrind should show if it does leak.)
... it does leak memory at present. :-| (See attached commit log for
details for one example.)
(Attached "Fix 'hash_table::expand' to destruct stale Value objects"
again.)
To that effect, to document the current behavior, I propose to
"Add more self-tests for 'hash_map' with Value type with non-trivial
constructor/destructor"
(We've done that in commit e4f16e9f357a38ec702fb69a0ffab9d292a6af9b
"Add more self-tests for 'hash_map' with Value type with non-trivial
constructor/destructor", quickly followed by bug fix
commit bb04a03c6f9bacc890118b9e12b657503093c2f8
"Make 'gcc/hash-map-tests.c:test_map_of_type_with_ctor_and_dtor_expand'
work on 32-bit architectures [PR101959]".
(Also cherry-pick into release branches, eventually?)
Then:
record_field_map_t field_map ([...]); // see below
for ([...])
{
tree record_type = [...];
[...]
bool existed;
field_map_t &fields
= field_map.get_or_insert (record_type, &existed);
gcc_checking_assert (!existed);
[...]
for ([...])
fields.put ([...], [...]);
[...]
}
[stuff that looks up elements from 'field_map']
field_map.empty ();
This generally works.
If I instantiate 'record_field_map_t field_map (40);', Valgrind is happy.
If however I instantiate 'record_field_map_t field_map (13);' (where '13'
would be the default for 'hash_map'), Valgrind complains:
2,080 bytes in 10 blocks are definitely lost in loss record 828 of 876
at 0x483DD99: calloc (vg_replace_malloc.c:762)
by 0x175F010: xcalloc (xmalloc.c:162)
by 0xAF4A2C: hash_table, tree_node*> >::hash_entry, false,
xcallocator>::hash_table(unsigned long, bool, bool, bool, mem_alloc_origin) (hash-table.h:275)
by 0x15E0120: hash_map, tree_node*>
>::hash_map(unsigned long, bool, bool, bool) (hash-map.h:143)
by 0x15DEE87: hash_map, tree_node*> >,
simple_hashmap_traits, hash_map, tree_node*> > > >::get_or_insert(tree_node* const&,
bool*) (hash-map.h:205)
by 0x15DD52C: execute_omp_oacc_neuter_broadcast()
(omp-oacc-neuter-broadcast.cc:1371)
[...]
(That's with '#pragma GCC optimize "O0"' at the top of the 'gcc/*.cc'
file.)
My suspicion was that it is due to the 'field_map' getting resized as it
incrementally grows (and '40' being big enough for that to never happen),
and somehow the non-POD (?) value objects not being properly handled
during that. Working my way a bit through 'gcc/hash-map.*' and
'gcc/hash-table.*' (but not claiming that I understand all that, off
hand), it seems as if my theory is right: I'm able to plug this
