Re: [PATCH][RFC] Sanitize equals and hash functions in hash-tables.

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jun 12, 2019 at 11:15 AM Martin Liška <mliska@suse.cz> wrote:
>
> On 6/12/19 10:02 AM, Martin Liška wrote:
> > On 6/12/19 9:59 AM, Richard Biener wrote:
> >> On Tue, Jun 11, 2019 at 9:02 PM Jason Merrill <jason@redhat.com> wrote:
> >>>
> >>> On 6/11/19 9:16 AM, Martin Liška wrote:
> >>>> On 6/11/19 2:27 PM, Jason Merrill wrote:
> >>>>> On 6/11/19 3:41 AM, Martin Liška wrote:
> >>>>>> On 6/10/19 8:21 PM, Jason Merrill wrote:
> >>>>>>> On Mon, Jun 10, 2019 at 3:08 AM Martin Liška <mliska@suse.cz> wrote:
> >>>>>>>> On 6/7/19 11:43 PM, Jason Merrill wrote:
> >>>>>>>>> On Fri, Jun 7, 2019 at 8:14 AM Martin Liška <mliska@suse.cz> wrote:
> >>>>>>>>>> On 6/7/19 2:09 PM, Richard Biener wrote:
> >>>>>>>>>>> On Fri, Jun 7, 2019 at 2:03 PM Martin Liška <mliska@suse.cz> wrote:
> >>>>>>>>>>>> On 6/7/19 10:57 AM, Richard Biener wrote:
> >>>>>>>>>>>>> On Mon, Jun 3, 2019 at 3:35 PM Martin Liška <mliska@suse.cz> wrote:
> >>>>>>>>>>>>>> On 6/1/19 12:06 AM, Jeff Law wrote:
> >>>>>>>>>>>>>>> On 5/22/19 3:13 AM, Martin Liška wrote:
> >>>>>>>>>>>>>>>> On 5/21/19 1:51 PM, Richard Biener wrote:
> >>>>>>>>>>>>>>>>> On Tue, May 21, 2019 at 1:02 PM Martin Liška <mliska@suse.cz> wrote:
> >>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> On 5/21/19 11:38 AM, Richard Biener wrote:
> >>>>>>>>>>>>>>>>>>> On Tue, May 21, 2019 at 12:07 AM Jeff Law <law@redhat.com> wrote:
> >>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>> On 5/13/19 1:41 AM, Martin Liška wrote:
> >>>>>>>>>>>>>>>>>>>>> On 11/8/18 9:56 AM, Martin Liška wrote:
> >>>>>>>>>>>>>>>>>>>>>> On 11/7/18 11:23 PM, Jeff Law wrote:
> >>>>>>>>>>>>>>>>>>>>>>> On 10/30/18 6:28 AM, Martin Liška wrote:
> >>>>>>>>>>>>>>>>>>>>>>>> On 10/30/18 11:03 AM, Jakub Jelinek wrote:
> >>>>>>>>>>>>>>>>>>>>>>>>> On Mon, Oct 29, 2018 at 04:14:21PM +0100, Martin Liška wrote:
> >>>>>>>>>>>>>>>>>>>>>>>>>> +hashtab_chk_error ()
> >>>>>>>>>>>>>>>>>>>>>>>>>> +{
> >>>>>>>>>>>>>>>>>>>>>>>>>> +  fprintf (stderr, "hash table checking failed: "
> >>>>>>>>>>>>>>>>>>>>>>>>>> +           "equal operator returns true for a pair "
> >>>>>>>>>>>>>>>>>>>>>>>>>> +           "of values with a different hash value");
> >>>>>>>>>>>>>>>>>>>>>>>>> BTW, either use internal_error here, or at least if using fprintf
> >>>>>>>>>>>>>>>>>>>>>>>>> terminate with \n, in your recent mail I saw:
> >>>>>>>>>>>>>>>>>>>>>>>>> ...different hash valueduring RTL pass: vartrack
> >>>>>>>>>>>>>>>>>>>>>>>>>                       ^^^^^^
> >>>>>>>>>>>>>>>>>>>>>>>> Sure, fixed in attached patch.
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>> Martin
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>>>> +  gcc_unreachable ();
> >>>>>>>>>>>>>>>>>>>>>>>>>> +}
> >>>>>>>>>>>>>>>>>>>>>>>>>     Jakub
> >>>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>> 0001-Sanitize-equals-and-hash-functions-in-hash-tables.patch
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>>   From 0d9c979c845580a98767b83c099053d36eb49bb9 Mon Sep 17 00:00:00 2001
> >>>>>>>>>>>>>>>>>>>>>>>> From: marxin <mliska@suse.cz>
> >>>>>>>>>>>>>>>>>>>>>>>> Date: Mon, 29 Oct 2018 09:38:21 +0100
> >>>>>>>>>>>>>>>>>>>>>>>> Subject: [PATCH] Sanitize equals and hash functions in hash-tables.
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>> ---
> >>>>>>>>>>>>>>>>>>>>>>>>    gcc/hash-table.h | 40 +++++++++++++++++++++++++++++++++++++++-
> >>>>>>>>>>>>>>>>>>>>>>>>    1 file changed, 39 insertions(+), 1 deletion(-)
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>> diff --git a/gcc/hash-table.h b/gcc/hash-table.h
> >>>>>>>>>>>>>>>>>>>>>>>> index bd83345c7b8..694eedfc4be 100644
> >>>>>>>>>>>>>>>>>>>>>>>> --- a/gcc/hash-table.h
> >>>>>>>>>>>>>>>>>>>>>>>> +++ b/gcc/hash-table.h
> >>>>>>>>>>>>>>>>>>>>>>>> @@ -503,6 +503,7 @@ private:
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>>      value_type *alloc_entries (size_t n CXX_MEM_STAT_INFO) const;
> >>>>>>>>>>>>>>>>>>>>>>>>      value_type *find_empty_slot_for_expand (hashval_t);
> >>>>>>>>>>>>>>>>>>>>>>>> +  void verify (const compare_type &comparable, hashval_t hash);
> >>>>>>>>>>>>>>>>>>>>>>>>      bool too_empty_p (unsigned int);
> >>>>>>>>>>>>>>>>>>>>>>>>      void expand ();
> >>>>>>>>>>>>>>>>>>>>>>>>      static bool is_deleted (value_type &v)
> >>>>>>>>>>>>>>>>>>>>>>>> @@ -882,8 +883,12 @@ hash_table<Descriptor, Allocator>
> >>>>>>>>>>>>>>>>>>>>>>>>      if (insert == INSERT && m_size * 3 <= m_n_elements * 4)
> >>>>>>>>>>>>>>>>>>>>>>>>        expand ();
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>> -  m_searches++;
> >>>>>>>>>>>>>>>>>>>>>>>> +#if ENABLE_EXTRA_CHECKING
> >>>>>>>>>>>>>>>>>>>>>>>> +    if (insert == INSERT)
> >>>>>>>>>>>>>>>>>>>>>>>> +      verify (comparable, hash);
> >>>>>>>>>>>>>>>>>>>>>>>> +#endif
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>> +  m_searches++;
> >>>>>>>>>>>>>>>>>>>>>>>>      value_type *first_deleted_slot = NULL;
> >>>>>>>>>>>>>>>>>>>>>>>>      hashval_t index = hash_table_mod1 (hash, m_size_prime_index);
> >>>>>>>>>>>>>>>>>>>>>>>>      hashval_t hash2 = hash_table_mod2 (hash, m_size_prime_index);
> >>>>>>>>>>>>>>>>>>>>>>>> @@ -930,6 +935,39 @@ hash_table<Descriptor, Allocator>
> >>>>>>>>>>>>>>>>>>>>>>>>      return &m_entries[index];
> >>>>>>>>>>>>>>>>>>>>>>>>    }
> >>>>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>>> +#if ENABLE_EXTRA_CHECKING
> >>>>>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>>>>> +/* Report a hash table checking error.  */
> >>>>>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>>>>> +ATTRIBUTE_NORETURN ATTRIBUTE_COLD
> >>>>>>>>>>>>>>>>>>>>>>>> +static void
> >>>>>>>>>>>>>>>>>>>>>>>> +hashtab_chk_error ()
> >>>>>>>>>>>>>>>>>>>>>>>> +{
> >>>>>>>>>>>>>>>>>>>>>>>> +  fprintf (stderr, "hash table checking failed: "
> >>>>>>>>>>>>>>>>>>>>>>>> +     "equal operator returns true for a pair "
> >>>>>>>>>>>>>>>>>>>>>>>> +     "of values with a different hash value\n");
> >>>>>>>>>>>>>>>>>>>>>>>> +  gcc_unreachable ();
> >>>>>>>>>>>>>>>>>>>>>>>> +}
> >>>>>>>>>>>>>>>>>>>>>>> I think an internal_error here is probably still better than a simple
> >>>>>>>>>>>>>>>>>>>>>>> fprintf, even if the fprintf is terminated with a \n :-)
> >>>>>>>>>>>>>>>>>>>>>> Fully agree with that, but I see a lot of build errors when using internal_error.
> >>>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>>>> The question then becomes can we bootstrap with this stuff enabled and
> >>>>>>>>>>>>>>>>>>>>>>> if not, are we likely to soon?  It'd be a shame to put it into
> >>>>>>>>>>>>>>>>>>>>>>> EXTRA_CHECKING, but then not be able to really use EXTRA_CHECKING
> >>>>>>>>>>>>>>>>>>>>>>> because we've got too many bugs to fix.
> >>>>>>>>>>>>>>>>>>>>>> Unfortunately it's blocked with these 2 PRs:
> >>>>>>>>>>>>>>>>>>>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87845
> >>>>>>>>>>>>>>>>>>>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87847
> >>>>>>>>>>>>>>>>>>>>> Hi.
> >>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>> I've just added one more PR:
> >>>>>>>>>>>>>>>>>>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90450
> >>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>> I'm sending updated version of the patch that provides a disablement for the 3 PRs
> >>>>>>>>>>>>>>>>>>>>> with a new function disable_sanitize_eq_and_hash.
> >>>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>> With that I can bootstrap and finish tests. However, I've done that with a patch
> >>>>>>>>>>>>>>>>>>>>> limits maximal number of checks:
> >>>>>>>>>>>>>>>>>>>> So rather than call the disable_sanitize_eq_and_hash, can you have its
> >>>>>>>>>>>>>>>>>>>> state set up when you instantiate the object?  It's not a huge deal,
> >>>>>>>>>>>>>>>>>>>> just thinking about loud.
> >>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>> So how do we want to go forward, particularly the EXTRA_EXTRA checking
> >>>>>>>>>>>>>>>>>>>> issue :-)
> >>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>> There is at least one PR where we have a table where elements _in_ the
> >>>>>>>>>>>>>>>>>>> table are never compared against each other but always against another
> >>>>>>>>>>>>>>>>>>> object (I guess that's usual even), but the setup is in a way that the
> >>>>>>>>>>>>>>>>>>> comparison function only works with those.  With the patch we verify
> >>>>>>>>>>>>>>>>>>> hashing/comparison for something that is never used.
> >>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>> So - wouldn't it be more "correct" to only verify comparison/hashing
> >>>>>>>>>>>>>>>>>>> at lookup time, using the object from the lookup and verify that against
> >>>>>>>>>>>>>>>>>>> all other elements?
> >>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> I don't a have problem with that. Apparently this changes fixes
> >>>>>>>>>>>>>>>>>> PR90450 and PR87847.
> >>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> Changes from previous version:
> >>>>>>>>>>>>>>>>>> - verification happens only when an element is searched (not inserted)
> >>>>>>>>>>>>>>>>>> - new argument 'sanitize_eq_and_hash' added for hash_table::hash_table
> >>>>>>>>>>>>>>>>>> - new param has been introduced hash-table-verification-limit in order
> >>>>>>>>>>>>>>>>>>     to limit number of elements that are compared within a table
> >>>>>>>>>>>>>>>>>> - verification happens only with flag_checking >= 2
> >>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> I've been bootstrapping and testing the patch right now.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>> Looks like I misremembered the original patch.  The issue isn't
> >>>>>>>>>>>>>>>>> comparing random two elements in the table.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>> That it fixes PR90450 is because LIM never calls find_slot_with_hash
> >>>>>>>>>>>>>>>>> without INSERTing.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> There's updated version of the patch where I check all find operations
> >>>>>>>>>>>>>>>> (both w/ and w/o insertion).
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests
> >>>>>>>>>>>>>>>> except for:
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> $ ./xgcc -B. /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/torture/pr63941.c -O2 -c
> >>>>>>>>>>>>>>>> hash table checking failed: equal operator returns true for a pair of values with a different hash value
> >>>>>>>>>>>>>>>> during GIMPLE pass: lim
> >>>>>>>>>>>>>>>> /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/torture/pr63941.c: In function ‘fn1’:
> >>>>>>>>>>>>>>>> /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/torture/pr63941.c:6:1: internal compiler error: in hashtab_chk_error, at hash-table.h:1019
> >>>>>>>>>>>>>>>>       6 | fn1 ()
> >>>>>>>>>>>>>>>>         | ^~~
> >>>>>>>>>>>>>>>> 0x6c5725 hashtab_chk_error
> >>>>>>>>>>>>>>>>        /home/marxin/Programming/gcc/gcc/hash-table.h:1019
> >>>>>>>>>>>>>>>> 0xe504ea hash_table<mem_ref_hasher, false, xcallocator>::verify(ao_ref* const&, unsigned int)
> >>>>>>>>>>>>>>>>        /home/marxin/Programming/gcc/gcc/hash-table.h:1040
> >>>>>>>>>>>>>>>> 0xe504ea hash_table<mem_ref_hasher, false, xcallocator>::find_slot_with_hash(ao_ref* const&, unsigned int, insert_option)
> >>>>>>>>>>>>>>>>        /home/marxin/Programming/gcc/gcc/hash-table.h:960
> >>>>>>>>>>>>>>>> 0xe504ea gather_mem_refs_stmt
> >>>>>>>>>>>>>>>>        /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:1501
> >>>>>>>>>>>>>>>> 0xe504ea analyze_memory_references
> >>>>>>>>>>>>>>>>        /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:1625
> >>>>>>>>>>>>>>>> 0xe504ea tree_ssa_lim
> >>>>>>>>>>>>>>>>        /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:2646
> >>>>>>>>>>>>>>>> 0xe504ea execute
> >>>>>>>>>>>>>>>>        /home/marxin/Programming/gcc/gcc/tree-ssa-loop-im.c:2708
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> Richi: it's after your recent patch.
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> For some reason I don't see PR87847 issue any longer.
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> May I install the patch with disabled sanitization in tree-ssa-loop-im.c ?
> >>>>>>>>>>>>>>> Don't we still need to deal with the naked fprintf when there's a
> >>>>>>>>>>>>>>> failure.  ie, shouldn't we be raising it with a gcc_assert or somesuch?
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Good point, I've just adjusted that.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Ready to be installed?
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Ugh, the cselib one is really bad.  But I don't hold my breath for anyone
> >>>>>>>>>>>>> fixing it ...
> >>>>>>>>>>>>
> >>>>>>>>>>>> Yes :D It's been some time and there's no interest in the PR.
> >>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> One question - there's unconditional
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> +         if (m_sanitize_eq_and_hash)
> >>>>>>>>>>>>> +           verify (comparable, hash);
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> which will read a global variable and have (possibly not inline) call
> >>>>>>>>>>>>> to verify on a common path even with checking disabled.  So I think
> >>>>>>>>>>>>> we want to compile this checking feature out for !CHECKING_P
> >>>>>>>>>>>>> or at least make the if __builtin_expect (..., 0), ::verify not
> >>>>>>>>>>>>> inlined and marked pure () (thus, !CHECKING_P is simplest ;)).
> >>>>>>>>>>>>
> >>>>>>>>>>>> Fixed. May I install the patch? The cselib issue can be solved later..
> >>>>>>>>>>>
> >>>>>>>>>>> You missed the second occurance
> >>>>>>>>>>>
> >>>>>>>>>>> -  m_searches++;
> >>>>>>>>>>> +  if (m_sanitize_eq_and_hash)
> >>>>>>>>>>> +    verify (comparable, hash);
> >>>>>>>>>>
> >>>>>>>>>> Yep ;) I've just install the patch.
> >>>>>>>>>
> >>>>>>>>> This is breaking my build:
> >>>>>>>>>
> >>>>>>>>> /home/jason/gt/gcc/hash-map.h:123:71: error: no matching function for
> >>>>>>>>> call to ‘hash_table<hash_map<mem_alloc_d\
> >>>>>>>>> escription<mem_usage>::mem_location_hash, mem_usage*,
> >>>>>>>>> simple_hashmap_traits<default_hash_traits<mem_alloc_desc\
> >>>>>>>>> ription<mem_usage>::mem_location_hash>, mem_usage*> >::hash_entry,
> >>>>>>>>> false, xcallocator>::hash_table(size_t&, bo\
> >>>>>>>>> ol&, bool&, mem_alloc_origin, const char*&, int&, const char*&)’
> >>>>>>>>>        : m_table (n, ggc, gather_mem_stats, HASH_MAP_ORIGIN PASS_MEM_STAT) {}
> >>>>>>>>>
> >>>>>>>>> Looks like this needs to be updated to pass an argument to the new
> >>>>>>>>> sanitize_eq_and_hash parameter.
> >>>>>>>>>
> >>>>>>>>> Jason
> >>>>>>>>
> >>>>>>>> Sorry for the breakage, I've just fixed that in r272104.
> >>>>>>>
> >>>>>>> Thanks.  I'm also seeing a massive compile time hit from this:  A
> >>>>>>> constexpr testcase that I've been looking at went from compiling in 13
> >>>>>>> seconds to 78 seconds, 6 times as long.  I would expect template-heavy
> >>>>>>> code to see similar problems when sanitization is enabled for those
> >>>>>>> hash tables.  Could we keep the parameter low or 0 by default, and
> >>>>>>> just do occasional sanitize runs with it explicitly enabled?
> >>>>>>
> >>>>>> Makes sense to me. Can you please provide a test-case which I can measure?
> >>>>>
> >>>>> This is the one I've been looking at:
> >>>>>
> >>>>>    struct Int {
> >>>>>      constexpr Int(int v): v(v) {}
> >>>>>      constexpr Int& operator+=(Int b) { this->v += b.v; return *this; }
> >>>>>      constexpr Int& operator++() { ++this->v; return *this; }
> >>>>>    private:
> >>>>>      friend constexpr bool operator<(Int a, Int b) { return a.v < b.v; }
> >>>>>      int v;
> >>>>>    };
> >>>>>    constexpr int f(int n) {
> >>>>>      Int i = {0};
> >>>>>      Int k = {0};
> >>>>>      k = 0;
> >>>>>      for (; k<10000; ++k) {
> >>>>>        i += k;
> >>>>>      }
> >>>>>      return n;
> >>>>>    }
> >>>>>
> >>>>>    template<int N> struct S {
> >>>>>      static constexpr int sm = S<N-1>::sm+f(N);
> >>>>>    };
> >>>>>    template<> struct S<0> {
> >>>>>      static constexpr int sm = 0;
> >>>>>    };
> >>>>>    constexpr int r = S<20>::sm;
> >>>>>
> >>>>> Jason
> >>>>
> >>>> For the test-case provided I see:
> >>>>
> >>>> $ time g++ time.cc -c --param hash-table-verification-limit=100
> >>>>
> >>>> real  0m1.855s
> >>>> user  0m1.829s
> >>>> sys   0m0.025s
> >>>>
> >>>> $ time g++ time.cc -c --param hash-table-verification-limit=0
> >>>>
> >>>> real  0m1.275s
> >>>> user  0m1.219s
> >>>> sys   0m0.052s
> >>>>
> >>>> $ time g++-9 time.cc -c
> >>>>
> >>>> real  0m0.939s
> >>>> user  0m0.827s
> >>>> sys   0m0.109s
> >>>>
> >>>> So it's slower, but I can't confirm the huge slowdown you see.
> >>>> Is it due to r272144?
> >>>
> >>> Hmm, I wonder if this is because of the
> >>> --enable-gather-detailed-mem-stats hash tables.
> >>
> >> I wonder if we can reduce the overhead by making
> >> hash-tables/maps using predefined traits not perform
> >> the checking?  Thus make [the default] whether to check or not
> >> to check part of the traits?  Surely the basic pointer-hash/map
> >> stuff is OK and needs no extra checking.
> >
> > Interesting idea! I can prepare a patch. Right now I'm testing a patch
> > that removes sanitization for hash-tables (and maps) that track memory
> > allocations.
>
> I've got 2 patch candidates that will make it happen. It survives build
> on --enable-languages=all, but one would need to build all cross-compilers
> to make a proper testing.
>
> Do you like the idea of the patch before I'll write a changelog and test it?

The disabling for mem-stats patch looks good to me.  I don't like the
implementation of the traits one, we don't want to have to put the
default returning true everywhere.  Instead I expected some
enable_if <> magic to do select a default true if the member isn't
present.  The issue with the traits idea is also that people like
to derive from one of the standard traits and thus might inherit
'false' even though they override hash/compare methods.  That is,
I expected

+template <typename Type>
+inline bool
+pointer_hash <Type>::sanitize ()
+{
+  return true;
+}

to return false for example.  Basically for the case we
auto-detect the traits based on the key type I wanted to
disable sanitizing and for custom users leave them to
per-object decisions.

Not sure if we have enough C++ power to make that happen easily.
So let's go the route of disabling the "ovbiously" correct and performance
critical parts for now.

Richard.

> Thanks,
> Martin
>
> >
> > Martin
> >
> >>
> >> Richard.
> >>
> >>> Jason
> >
>