[C++ PATCH] Fix concepts vs. PCH (PR c++/92458, take 2)

[Jakub Jelinek]

On Fri, Nov 22, 2019 at 02:43:25PM -0500, Jason Merrill wrote:
> > @@ -5358,6 +5410,18 @@ struct tree_cache_traits
> >     : simple_cache_map_traits<default_hash_traits<tree>, tree> { };
> 
> We should probably use tree_hash instead of default_hash_traits here. OK
> with or without that change.

Dunno, I'd say pointer_hash <Type>::hash which is
  return (hashval_t) ((intptr_t)candidate >> 3);
might be actually better hash function than
#define TREE_HASH(NODE) ((size_t) (NODE) & 0777777)
at least on 64-bit hosts, because union tree_node is 8-byte aligned there,
so the low 3 bits are all zero and we use all of the 32 bits above that.
For 32-bit hosts, it might be better to just use candidate without shifting
I guess, there aren't any extra bits we get in from above.
TREE_HASH to me unnecessarily uses the low 3 bits known to be zero and masks
with 0x3ffff, so throws away also 14 bits that could hold useful info,
leaving for 64-bit hosts only 15 bits.

	Jakub