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

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

On Wed, Jun 12, 2019 at 1:45 PM Martin Liška <mliska@suse.cz> wrote:
>
> On 6/12/19 11:41 AM, Richard Biener wrote:
> > 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.
>
> Huh, I've tried quite hard and I was unable to make it happen. Maybe
> somebody more familiar with C++ can step in?
>
> > So let's go the route of disabling the "ovbiously" correct and performance
> > critical parts for now.
>
> I'm sending patch for it.

   explicit hash_map (size_t n = 13, bool ggc = false,
+                    bool sanitize_eq_and_hash = true,
                     bool gather_mem_stats = GATHER_STATISTICS
                     CXX_MEM_STAT_INFO)

maybe not an issue here but adding defaulted params into the
middle is prone to change existing calls semantics.  Consider

 hash_map (13, false, false);

which was gather_mem_stats == false before but now is
sanitize_eq_and_hash.  I realize the original patch had the
same issue.

Patch is still OK.

Please grep for explicit constructor calls and double-check.
Ick.  I guess also

   hash_map<foo, bar> baz (13, false, false);

is affected so make sure to apply enough grep-fu.

New params should always go to the end ;)

Richard.

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