py: Optimise types for common case where type has a single parent type.

The common cases for inheritance are 0 or 1 parent types, for both built-in
types (eg built-in exceptions) as well as user defined types.  So it makes
sense to optimise the case of 1 parent type by storing just the type and
not a tuple of 1 value (that value being the single parent type).

This patch makes such an optimisation.  Even though there is a bit more
code to handle the two cases (either a single type or a tuple with 2 or
more values) it helps reduce overall code size because it eliminates the
need to create a static tuple to hold single parents (eg for the built-in
exceptions).  It also helps reduce RAM usage for user defined types that
only derive from a single parent.

Changes in code size (in bytes) due to this patch:

    bare-arm:       -16
    minimal (x86): -176
    unix (x86-64): -320
    unix nanbox:   -384
    stmhal:         -64
    cc3200:         -32
    esp8266:       -108

1 files changed, 1 insertions, 16 deletions

diff --git a/py/objexcept.c b/py/objexcept.c
index dcc7800dc..4722aca91 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -197,9 +197,6 @@ const mp_obj_type_t mp_type_BaseException = {
     .locals_dict = (mp_obj_dict_t*)&exc_locals_dict,
 };
 
-#define MP_DEFINE_EXCEPTION_BASE(base_name) \
-STATIC const mp_rom_obj_tuple_t mp_type_ ## base_name ## _base_tuple = {{&mp_type_tuple}, 1, {MP_ROM_PTR(&mp_type_ ## base_name)}};\
-
 #define MP_DEFINE_EXCEPTION(exc_name, base_name) \
 const mp_obj_type_t mp_type_ ## exc_name = { \
     { &mp_type_type }, \
@@ -207,23 +204,20 @@ const mp_obj_type_t mp_type_ ## exc_name = { \
     .print = mp_obj_exception_print, \
     .make_new = mp_obj_exception_make_new, \
     .attr = exception_attr, \
-    .bases_tuple = (mp_obj_tuple_t*)(mp_rom_obj_tuple_t*)&mp_type_ ## base_name ## _base_tuple, \
+    .parent = &mp_type_ ## base_name, \
 };
 
 // List of all exceptions, arranged as in the table at:
 // http://docs.python.org/3/library/exceptions.html
-MP_DEFINE_EXCEPTION_BASE(BaseException)
 MP_DEFINE_EXCEPTION(SystemExit, BaseException)
 MP_DEFINE_EXCEPTION(KeyboardInterrupt, BaseException)
 MP_DEFINE_EXCEPTION(GeneratorExit, BaseException)
 MP_DEFINE_EXCEPTION(Exception, BaseException)
-  MP_DEFINE_EXCEPTION_BASE(Exception)
   #if MICROPY_PY_ASYNC_AWAIT
   MP_DEFINE_EXCEPTION(StopAsyncIteration, Exception)
   #endif
   MP_DEFINE_EXCEPTION(StopIteration, Exception)
   MP_DEFINE_EXCEPTION(ArithmeticError, Exception)
-    MP_DEFINE_EXCEPTION_BASE(ArithmeticError)
     //MP_DEFINE_EXCEPTION(FloatingPointError, ArithmeticError)
     MP_DEFINE_EXCEPTION(OverflowError, ArithmeticError)
     MP_DEFINE_EXCEPTION(ZeroDivisionError, ArithmeticError)
@@ -235,18 +229,15 @@ MP_DEFINE_EXCEPTION(Exception, BaseException)
   MP_DEFINE_EXCEPTION(ImportError, Exception)
   //MP_DEFINE_EXCEPTION(IOError, Exception) use OSError instead
   MP_DEFINE_EXCEPTION(LookupError, Exception)
-    MP_DEFINE_EXCEPTION_BASE(LookupError)
     MP_DEFINE_EXCEPTION(IndexError, LookupError)
     MP_DEFINE_EXCEPTION(KeyError, LookupError)
   MP_DEFINE_EXCEPTION(MemoryError, Exception)
   MP_DEFINE_EXCEPTION(NameError, Exception)
     /*
-    MP_DEFINE_EXCEPTION_BASE(NameError)
     MP_DEFINE_EXCEPTION(UnboundLocalError, NameError)
     */
   MP_DEFINE_EXCEPTION(OSError, Exception)
 #if MICROPY_PY_BUILTINS_TIMEOUTERROR
-    MP_DEFINE_EXCEPTION_BASE(OSError)
     MP_DEFINE_EXCEPTION(TimeoutError, OSError)
 #endif
     /*
@@ -267,30 +258,24 @@ MP_DEFINE_EXCEPTION(Exception, BaseException)
     MP_DEFINE_EXCEPTION(ReferenceError, Exception)
     */
   MP_DEFINE_EXCEPTION(RuntimeError, Exception)
-    MP_DEFINE_EXCEPTION_BASE(RuntimeError)
     MP_DEFINE_EXCEPTION(NotImplementedError, RuntimeError)
   MP_DEFINE_EXCEPTION(SyntaxError, Exception)
-    MP_DEFINE_EXCEPTION_BASE(SyntaxError)
     MP_DEFINE_EXCEPTION(IndentationError, SyntaxError)
     /*
-      MP_DEFINE_EXCEPTION_BASE(IndentationError)
       MP_DEFINE_EXCEPTION(TabError, IndentationError)
       */
   //MP_DEFINE_EXCEPTION(SystemError, Exception)
   MP_DEFINE_EXCEPTION(TypeError, Exception)
 #if MICROPY_EMIT_NATIVE
-    MP_DEFINE_EXCEPTION_BASE(TypeError)
     MP_DEFINE_EXCEPTION(ViperTypeError, TypeError)
 #endif
   MP_DEFINE_EXCEPTION(ValueError, Exception)
 #if MICROPY_PY_BUILTINS_STR_UNICODE
-    MP_DEFINE_EXCEPTION_BASE(ValueError)
     MP_DEFINE_EXCEPTION(UnicodeError, ValueError)
     //TODO: Implement more UnicodeError subclasses which take arguments
 #endif
   /*
   MP_DEFINE_EXCEPTION(Warning, Exception)
-    MP_DEFINE_EXCEPTION_BASE(Warning)
     MP_DEFINE_EXCEPTION(DeprecationWarning, Warning)
     MP_DEFINE_EXCEPTION(PendingDeprecationWarning, Warning)
     MP_DEFINE_EXCEPTION(RuntimeWarning, Warning)