py: Store bytecode arg names in bytecode (were in own array).

This saves a lot of RAM for 2 reasons:

1. For functions that don't have default values, var args or var kw
args (which is a large number of functions in the general case), the
mp_obj_fun_bc_t type now fits in 1 GC block (previously needed 2 because
of the extra pointer to point to the arg_names array).  So this saves 16
bytes per function (32 bytes on 64-bit machines).

2. Combining separate memory regions generally saves RAM because the
unused bytes at the end of the GC block are saved for 1 of the blocks
(since that block doesn't exist on its own anymore).  So generally this
saves 8 bytes per function.

Tested by importing lots of modules:

- 64-bit Linux gave about an 8% RAM saving for 86k of used RAM.
- pyboard gave about a 6% RAM saving for 31k of used RAM.

1 files changed, 5 insertions, 3 deletions

diff --git a/py/objfun.c b/py/objfun.c
index e64d088bf..3adf05e3b 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -173,7 +173,10 @@ STATIC mp_obj_t fun_bc_call(mp_obj_t self_in, mp_uint_t n_args, mp_uint_t n_kw,
     mp_uint_t code_info_size = mp_decode_uint(&code_info);
     const byte *ip = self->bytecode + code_info_size;
 
-    // bytecode prelude: state size and exception stack size; 16 bit uints
+    // bytecode prelude: skip arg names
+    ip += (self->n_pos_args + self->n_kwonly_args) * sizeof(mp_obj_t);
+
+    // bytecode prelude: state size and exception stack size
     mp_uint_t n_state = mp_decode_uint(&ip);
     mp_uint_t n_exc_stack = mp_decode_uint(&ip);
 
@@ -268,7 +271,7 @@ const mp_obj_type_t mp_type_fun_bc = {
     .binary_op = mp_obj_fun_binary_op,
 };
 
-mp_obj_t mp_obj_new_fun_bc(mp_uint_t scope_flags, qstr *args, mp_uint_t n_pos_args, mp_uint_t n_kwonly_args, mp_obj_t def_args_in, mp_obj_t def_kw_args, const byte *code) {
+mp_obj_t mp_obj_new_fun_bc(mp_uint_t scope_flags, mp_uint_t n_pos_args, mp_uint_t n_kwonly_args, mp_obj_t def_args_in, mp_obj_t def_kw_args, const byte *code) {
     mp_uint_t n_def_args = 0;
     mp_uint_t n_extra_args = 0;
     mp_obj_tuple_t *def_args = def_args_in;
@@ -283,7 +286,6 @@ mp_obj_t mp_obj_new_fun_bc(mp_uint_t scope_flags, qstr *args, mp_uint_t n_pos_ar
     mp_obj_fun_bc_t *o = m_new_obj_var(mp_obj_fun_bc_t, mp_obj_t, n_extra_args);
     o->base.type = &mp_type_fun_bc;
     o->globals = mp_globals_get();
-    o->args = args;
     o->n_pos_args = n_pos_args;
     o->n_kwonly_args = n_kwonly_args;
     o->n_def_args = n_def_args;