py/vm: Add a fast path for LOAD_ATTR on instance types.

When the LOAD_ATTR opcode is executed there are quite a few different cases
that have to be handled, but the common case is accessing a member on an
instance type.  Typically, built-in types provide methods which is why this
is common.

Fortunately, for this specific case, if the member is found in the member
map then there's no further processing.

This optimisation does a relatively cheap check (type is instance) and then
forwards directly to the member map lookup, falling back to the regular
path if necessary.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/py/vm.c b/py/vm.c
index bbfc9914e..e5a62e441 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -414,7 +414,26 @@ dispatch_loop:
                     FRAME_UPDATE();
                     MARK_EXC_IP_SELECTIVE();
                     DECODE_QSTR;
-                    SET_TOP(mp_load_attr(TOP(), qst));
+                    mp_obj_t top = TOP();
+                    mp_obj_t obj;
+                    #if MICROPY_OPT_LOAD_ATTR_FAST_PATH
+                    // For the specific case of an instance type, it implements .attr
+                    // and forwards to its members map. Attribute lookups on instance
+                    // types are extremely common, so avoid all the other checks and
+                    // calls that normally happen first.
+                    mp_map_elem_t *elem = NULL;
+                    if (mp_obj_is_instance_type(mp_obj_get_type(top))) {
+                        mp_obj_instance_t *self = MP_OBJ_TO_PTR(top);
+                        elem = mp_map_lookup(&self->members, MP_OBJ_NEW_QSTR(qst), MP_MAP_LOOKUP);
+                    }
+                    if (elem) {
+                        obj = elem->value;
+                    } else
+                    #endif
+                    {
+                        obj = mp_load_attr(top, qst);
+                    }
+                    SET_TOP(obj);
                     DISPATCH();
                 }
                 #else