Re: hash-table violation in gcc/cp/pt.c

["Martin Liška" <mliska@suse.cz>]

On 10/30/18 11:25 AM, Martin Liška wrote:
> On 10/29/18 12:04 PM, Martin Liška wrote:
>> 3) lookup_template_class_1
>>
>> $ ./xg++ -B. /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/template/ttp23.C -c -fchecking=3
>> hash table checking failed: equal operator returns true for a pair of values with a different hash value/home/marxin/Programming/gcc/gcc/testsuite/g++.dg/template/ttp23.C: In instantiation of ‘struct B<A>’:
>> /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/template/ttp23.C:15:8:   required from here
>> /home/marxin/Programming/gcc/gcc/testsuite/g++.dg/template/ttp23.C:8:17: internal compiler error: in find_slot_with_hash, at hash-table.h:905
>>     8 |     friend bool foo (const B<Q>& a);
>>       |                 ^~~
>> 0xa265a4 hash_table<spec_hasher, xcallocator>::find_slot_with_hash(spec_entry* const&, unsigned int, insert_option)
>> 	/home/marxin/Programming/gcc/gcc/hash-table.h:905
>> 0xa042ce lookup_template_class_1
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:9629
>> 0xa042ce lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*, int, int)
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:9674
>> 0xa03670 tsubst_aggr_type
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:12679
>> 0x9fefcd tsubst(tree_node*, tree_node*, int, tree_node*)
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:14294
>> 0x9fe1a9 tsubst(tree_node*, tree_node*, int, tree_node*)
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:14285
>> 0xa0d8bd tsubst_arg_types
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:13891
>> 0xa0dc24 tsubst_function_type
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:14032
>> 0x9fe790 tsubst(tree_node*, tree_node*, int, tree_node*)
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:14769
>> 0x9f2c7c tsubst_function_decl
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:12921
>> 0xa02d27 tsubst_template_decl
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:13214
>> 0x9f4416 tsubst_decl
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:13316
>> 0x9ff0ca tsubst(tree_node*, tree_node*, int, tree_node*)
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:14212
>> 0xa1dfd0 tsubst_friend_function
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:10310
>> 0xa1dfd0 instantiate_class_template_1
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:11359
>> 0xa1dfd0 instantiate_class_template(tree_node*)
>> 	/home/marxin/Programming/gcc/gcc/cp/pt.c:11424
>> 0xa66b22 complete_type(tree_node*)
>> 	/home/marxin/Programming/gcc/gcc/cp/typeck.c:138
>> 0x9023c7 start_decl_1(tree_node*, bool)
>> 	/home/marxin/Programming/gcc/gcc/cp/decl.c:5278
>> 0x92a15f start_decl(cp_declarator const*, cp_decl_specifier_seq*, int, tree_node*, tree_node*, tree_node**)
>> 	/home/marxin/Programming/gcc/gcc/cp/decl.c:5241
>> 0x9c1944 cp_parser_init_declarator
>> 	/home/marxin/Programming/gcc/gcc/cp/parser.c:19750
> 
> This one is about inconsistency between:
> 
> /* Returns a hash for a template TMPL and template arguments ARGS.  */
> 
> static hashval_t
> hash_tmpl_and_args (tree tmpl, tree args)
> {
>   hashval_t val = iterative_hash_object (DECL_UID (tmpl), 0);
>   return iterative_hash_template_arg (args, val);
> }
> 
> iterative_hash_template_arg is problematic, differs from:
> bool
> spec_hasher::equal (spec_entry *e1, spec_entry *e2)
> {
>   int equal;
> 
>   ++comparing_specializations;
>   equal = (e1->tmpl == e2->tmpl
> 	   && comp_template_args (e1->args, e2->args));
> ...
> 
> where comp_template_args (e1->args, e2->args) returns true, but
> iterative_hash_template_arg values are different.
> 
> Can please some C++ maintainer take a look?
> 
> Thanks,
> Martin
> 

The same spec_hasher type is also involved in 4)

0xa265a4 hash_table<spec_hasher, xcallocator>::find_slot_with_hash(spec_entry* const&, unsigned int, insert_option)
	/home/marxin/Programming/gcc/gcc/hash-table.h:905
0x9e35e6 register_specialization
	/home/marxin/Programming/gcc/gcc/cp/pt.c:1534
0xa22ac3 check_explicit_specialization(tree_node*, tree_node*, int, int, tree_node*)
	/home/marxin/Programming/gcc/gcc/cp/pt.c:3243
0x91552d grokfndecl
	/home/marxin/Programming/gcc/gcc/cp/decl.c:9106
...

Martin