Structurally compare the few non-canonicalized types in general
In the abixml writer, we recently stopped using
type_base::dynamic_hash as a slow path to hash a non-canonicalized
type. Rather, we use an arbitrary constant as a hash for those
non-canonicalized types. This amounts to using structural comparison
for those types. The function that implements this hashing scheme is
hash_as_canonical_type_or_constant.
A potential concern for that approach was the possible negative impact
on speed. As it turns out since the change went in, there was no
noticeable speed impact raised after testing.
In insight, this is understandable as the number of non-canonicalized
types should be extremely reduced now that we canonicalize pretty much
all types. As far as I understand it at this point, the only types
that would not be canonicalized are unresolved declaration-only
types. And, all in all, structurally comparing unresolved
declaration-only types should be "fast enough".
If we ever stumble across any other non-canonicalized type, I think
that would be an artifact of a bug that ought to be fixed.
On that basis, I went ahead and used
hash_as_canonical_type_or_constant throughout the code base and did
away with the use of type_base::dynamic_hash for now, until it's
properly audited, regression tested and got ready for the use cases
where it might make sense.
This patch thus makes hash_type use
hash_as_canonical_type_or_constant. The writer is then back to using
hash_type again, as it used to; but at the same time, it's still using
structural comparison for non-canonilized types. So is
hash_type_or_decl, which now uses hash_type to hash types, rather than
using type_base::dynamic_hash. Note that the comparison engine
heavily uses hash_type_or_decl to hash diff nodes.
So with this small patch the comparison engine is now using structural
comparison of non-canonicalized types (and diff nodes), just as the
abixml writer does.
* include/abg-fwd.h (hash_as_canonical_type_or_constant): Remove
public declaration of this function.
* src/abg-hash.cc (type_base::dynamic_hash::operator()): Add a
comment.
* src/abg-ir.cc (hash_as_canonical_type_or_constant): Make this
function static now.
(hash_type_or_decl): Use hash_type for types.
* src/abg-writer.cc (type_hasher::operator()): Use hash_type.
Signed-off-by: Dodji Seketeli <dodji@redhat.com>
4 files changed
