[Bug c++/94454] ICE 'canonical types differ for identical types'

["nathan at acm dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94454

--- Comment #6 from Nathan Sidwell <nathan at acm dot org> ---
On 4/2/20 12:37 PM, iains at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94454
> 
> --- Comment #5 from Iain Sandoe <iains at gcc dot gnu.org> ---
> (In reply to Nathan Sidwell from comment #4)
>> Oh, it is from the template specialization hash table.  I suggest making
>> that very poor to increase collisions:
>>
>> pt.c:
>> static hashval_t
>> hash_tmpl_and_args (tree tmpl, tree args)
>> {
>>    hashval_t val = iterative_hash_object (DECL_UID (tmpl), 0);
>>     return val; // INSERT THIS LINE
>>    return iterative_hash_template_arg (args, val);
>> }
>>
>> sorry for not realizing this earlier
> 
> [not wishing to disturb the c-reduce sessions already started]
> 
> On Darwin17 @r10-7488, which was always succeeding
> 
> I bootstrapped with this patch, and then built a --disable-bootstrap with the
> "spec_hasher::hash always returns 0" applied too.

Ok, BTW spec_hasher::hash forwards to hash_tmpl_and_args.  They must 
agree, so ...

> Neither made any difference, the entire ranges-v3 suite built without issue.

surprises me.

> 
> Maybe that's informative in its own right.
> 
> Will hopefully have some kind of reduced test-case for x86-64-linux tomorrow.
>