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

[Jason Merrill <jason@redhat.com>]

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?

Jason