py: Remove mp_load_const_bytes and instead load precreated bytes object.

Previous to this patch each time a bytes object was referenced a new
instance (with the same data) was created.  With this patch a single
bytes object is created in the compiler and is loaded directly at execute
time as a true constant (similar to loading bignum and float objects).
This saves on allocating RAM and means that bytes objects can now be
used when the memory manager is locked (eg in interrupts).

The MP_BC_LOAD_CONST_BYTES bytecode was removed as part of this.

Generated bytecode is slightly larger due to storing a pointer to the
bytes object instead of the qstr identifier.

Code size is reduced by about 60 bytes on Thumb2 architectures.

1 files changed, 18 insertions, 9 deletions

diff --git a/py/compile.c b/py/compile.c
index 45217cfe99..141cd2db99 100644
--- a/py/compile.c
+++ b/py/compile.c
@@ -1078,7 +1078,7 @@ STATIC void compile_funcdef_param(compiler_t *comp, mp_parse_node_t pn) {
             if (comp->have_star) {
                 comp->num_dict_params += 1;
 #if MICROPY_EMIT_CPYTHON
-                EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pn_id), false);
+                EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pn_id));
                 compile_node(comp, pn_equal);
 #else
                 // in Micro Python we put the default dict parameters into a dictionary using the bytecode
@@ -1096,7 +1096,7 @@ STATIC void compile_funcdef_param(compiler_t *comp, mp_parse_node_t pn) {
 
                 // compile value then key, then store it to the dict
                 compile_node(comp, pn_equal);
-                EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pn_id), false);
+                EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pn_id));
                 EMIT(store_map);
 #endif
             } else {
@@ -1178,7 +1178,7 @@ STATIC qstr compile_classdef_helper(compiler_t *comp, mp_parse_node_struct_t *pn
     close_over_variables_etc(comp, cscope, 0, 0);
 
     // get its name
-    EMIT_ARG(load_const_str, cscope->simple_name, false);
+    EMIT_ARG(load_const_str, cscope->simple_name);
 
     // nodes[1] has parent classes, if any
     // empty parenthesis (eg class C():) gets here as an empty PN_classdef_2 and needs special handling
@@ -1553,7 +1553,7 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
 #if MICROPY_EMIT_CPYTHON
         EMIT_ARG(load_const_verbatim_strn, "('*',)", 6);
 #else
-        EMIT_ARG(load_const_str, MP_QSTR__star_, false);
+        EMIT_ARG(load_const_str, MP_QSTR__star_);
         EMIT_ARG(build_tuple, 1);
 #endif
 
@@ -1597,7 +1597,7 @@ STATIC void compile_import_from(compiler_t *comp, mp_parse_node_struct_t *pns) {
             assert(MP_PARSE_NODE_IS_STRUCT_KIND(pn_nodes[i], PN_import_as_name));
             mp_parse_node_struct_t *pns3 = (mp_parse_node_struct_t*)pn_nodes[i];
             qstr id2 = MP_PARSE_NODE_LEAF_ARG(pns3->nodes[0]); // should be id
-            EMIT_ARG(load_const_str, id2, false);
+            EMIT_ARG(load_const_str, id2);
         }
         EMIT_ARG(build_tuple, n);
 #endif
@@ -2531,7 +2531,7 @@ STATIC void compile_trailer_paren_helper(compiler_t *comp, mp_parse_node_t pn_ar
                         compile_syntax_error(comp, (mp_parse_node_t)pns_arg, "LHS of keyword arg must be an id");
                         return;
                     }
-                    EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pns_arg->nodes[0]), false);
+                    EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pns_arg->nodes[0]));
                     compile_node(comp, pns2->nodes[0]);
                     n_keyword += 1;
                 } else {
@@ -2979,8 +2979,17 @@ STATIC void compile_node(compiler_t *comp, mp_parse_node_t pn) {
         mp_uint_t arg = MP_PARSE_NODE_LEAF_ARG(pn);
         switch (MP_PARSE_NODE_LEAF_KIND(pn)) {
             case MP_PARSE_NODE_ID: compile_load_id(comp, arg); break;
-            case MP_PARSE_NODE_STRING: EMIT_ARG(load_const_str, arg, false); break;
-            case MP_PARSE_NODE_BYTES: EMIT_ARG(load_const_str, arg, true); break;
+            case MP_PARSE_NODE_STRING: EMIT_ARG(load_const_str, arg); break;
+            case MP_PARSE_NODE_BYTES:
+                // only create and load the actual bytes object on the last pass
+                if (comp->pass != MP_PASS_EMIT) {
+                    EMIT_ARG(load_const_obj, mp_const_none);
+                } else {
+                    mp_uint_t len;
+                    const byte *data = qstr_data(arg, &len);
+                    EMIT_ARG(load_const_obj, mp_obj_new_bytes(data, len));
+                }
+                break;
             case MP_PARSE_NODE_TOKEN: default:
                 if (arg == MP_TOKEN_NEWLINE) {
                     // this can occur when file_input lets through a NEWLINE (eg if file starts with a newline)
@@ -3367,7 +3376,7 @@ STATIC void compile_scope(compiler_t *comp, scope_t *scope, pass_kind_t pass) {
 
         compile_load_id(comp, MP_QSTR___name__);
         compile_store_id(comp, MP_QSTR___module__);
-        EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pns->nodes[0]), false); // 0 is class name
+        EMIT_ARG(load_const_str, MP_PARSE_NODE_LEAF_ARG(pns->nodes[0])); // 0 is class name
         compile_store_id(comp, MP_QSTR___qualname__);
 
         check_for_doc_string(comp, pns->nodes[2]);