py/obj: Add MICROPY_OBJ_IMMEDIATE_OBJS option to reduce code size.

This option (enabled by default for object representation A, B, C) makes
None/False/True objects immediate objects, ie they are no longer a concrete
object in ROM but are rather just values, eg None=0x6 for representation A.

Doing this saves a considerable amount of code size, due to these objects
being widely used:

   bare-arm:  -392 -0.591%
minimal x86:  -252 -0.170% [incl +52(data)]
   unix x64:  -624 -0.125% [incl -128(data)]
unix nanbox:    +0 +0.000%
      stm32: -1940 -0.510% PYBV10
     cc3200: -1216 -0.659%
    esp8266:  -404 -0.062% GENERIC
      esp32:  -732 -0.064% GENERIC[incl +48(data)]
        nrf:  -988 -0.675% pca10040
       samd:  -564 -0.556% ADAFRUIT_ITSYBITSY_M4_EXPRESS

Thanks go to @Jongy aka Yonatan Goldschmidt for the idea.

1 files changed, 24 insertions, 5 deletions

diff --git a/py/obj.h b/py/obj.h
index f0bb44a40..93433f924 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -263,13 +263,22 @@ typedef union _mp_rom_obj_t { uint64_t u64; struct { const void *lo, *hi; } u32;
 // Macros to create objects that are stored in ROM.
 
 #ifndef MP_ROM_NONE
+#if MICROPY_OBJ_IMMEDIATE_OBJS
+#define MP_ROM_NONE mp_const_none
+#else
 #define MP_ROM_NONE MP_ROM_PTR(&mp_const_none_obj)
 #endif
+#endif
 
 #ifndef MP_ROM_FALSE
+#if MICROPY_OBJ_IMMEDIATE_OBJS
+#define MP_ROM_FALSE mp_const_false
+#define MP_ROM_TRUE mp_const_true
+#else
 #define MP_ROM_FALSE MP_ROM_PTR(&mp_const_false_obj)
 #define MP_ROM_TRUE MP_ROM_PTR(&mp_const_true_obj)
 #endif
+#endif
 
 #ifndef MP_ROM_INT
 typedef mp_const_obj_t mp_rom_obj_t;
@@ -622,17 +631,27 @@ extern const mp_obj_type_t mp_type_ValueError;
 extern const mp_obj_type_t mp_type_ViperTypeError;
 extern const mp_obj_type_t mp_type_ZeroDivisionError;
 
-// Constant objects, globally accessible
-// The macros are for convenience only
+// Constant objects, globally accessible: None, False, True
+// These should always be accessed via the below macros.
+#if MICROPY_OBJ_IMMEDIATE_OBJS
+// None is even while False/True are odd so their types can be distinguished with 1 bit.
+#define mp_const_none MP_OBJ_NEW_IMMEDIATE_OBJ(0)
+#define mp_const_false MP_OBJ_NEW_IMMEDIATE_OBJ(1)
+#define mp_const_true MP_OBJ_NEW_IMMEDIATE_OBJ(3)
+#else
 #define mp_const_none (MP_OBJ_FROM_PTR(&mp_const_none_obj))
 #define mp_const_false (MP_OBJ_FROM_PTR(&mp_const_false_obj))
 #define mp_const_true (MP_OBJ_FROM_PTR(&mp_const_true_obj))
-#define mp_const_empty_bytes (MP_OBJ_FROM_PTR(&mp_const_empty_bytes_obj))
-#define mp_const_empty_tuple (MP_OBJ_FROM_PTR(&mp_const_empty_tuple_obj))
-#define mp_const_notimplemented (MP_OBJ_FROM_PTR(&mp_const_notimplemented_obj))
 extern const struct _mp_obj_none_t mp_const_none_obj;
 extern const struct _mp_obj_bool_t mp_const_false_obj;
 extern const struct _mp_obj_bool_t mp_const_true_obj;
+#endif
+
+// Constant objects, globally accessible: b'', (), Ellipsis, NotImplemented, GeneratorExit()
+// The below macros are for convenience only.
+#define mp_const_empty_bytes (MP_OBJ_FROM_PTR(&mp_const_empty_bytes_obj))
+#define mp_const_empty_tuple (MP_OBJ_FROM_PTR(&mp_const_empty_tuple_obj))
+#define mp_const_notimplemented (MP_OBJ_FROM_PTR(&mp_const_notimplemented_obj))
 extern const struct _mp_obj_str_t mp_const_empty_bytes_obj;
 extern const struct _mp_obj_tuple_t mp_const_empty_tuple_obj;
 extern const struct _mp_obj_singleton_t mp_const_ellipsis_obj;