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

[Jason Merrill <jason@redhat.com>]

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.

Jason