[Bug c++/87847] spec_hasher::hash does not match with spec_hasher::equal

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87847

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
In the ttp23.C testcase we're comparing B<Q> and B<Q>.  In one case the
template argument is

 <tree_vec 0x7fffeab33920 length:1
    elt:0 <template_template_parm 0x7fffeab3ad20 VOID
        align:8 warn_if_not_align:0 symtab:0 alias-set -1 structural-equality
       index 0 level 1 orig_level 2
        chain <template_decl 0x7fffea9f8b80 Q>>>

and the other is

 <tree_vec 0x7fffeab33560 length:1
    elt:0 <template_template_parm 0x7fffeab3a348 VOID
        align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7fffeab25c78
       index 0 level 1 orig_level 1
        chain <template_decl 0x7fffea9f8680 Q>>>

same_type_p says they're same, so comp_template_args returns true.  One of the
template_template_parms has TYPE_CANONICAL, so we hash it as:

 1905       if (TYPE_CANONICAL (arg))
 1906         return iterative_hash_object (TYPE_HASH (TYPE_CANONICAL (arg)),
 1907                                       val);

but the other type doesn't have a canonical type:

 1910       /* Otherwise just compare the types during lookup.  */
 1911       return val;

so the hashes end up being different.