py: Add mp_obj_new_str_from_vstr, and use it where relevant.

This patch allows to reuse vstr memory when creating str/bytes object.
This improves memory usage.

Also saves code ROM: 128 bytes on stmhal, 92 bytes on bare-arm, and 88
bytes on unix x64.

1 files changed, 4 insertions, 5 deletions

diff --git a/py/modbuiltins.c b/py/modbuiltins.c
index b739503ad..68a22934b 100644
--- a/py/modbuiltins.c
+++ b/py/modbuiltins.c
@@ -449,11 +449,10 @@ STATIC mp_obj_t mp_builtin___repl_print__(mp_obj_t o) {
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin___repl_print___obj, mp_builtin___repl_print__);
 
 STATIC mp_obj_t mp_builtin_repr(mp_obj_t o_in) {
-    vstr_t *vstr = vstr_new();
-    mp_obj_print_helper((void (*)(void *env, const char *fmt, ...))vstr_printf, vstr, o_in, PRINT_REPR);
-    mp_obj_t s = mp_obj_new_str(vstr->buf, vstr->len, false);
-    vstr_free(vstr);
-    return s;
+    vstr_t vstr;
+    vstr_init(&vstr, 16);
+    mp_obj_print_helper((void (*)(void *env, const char *fmt, ...))vstr_printf, &vstr, o_in, PRINT_REPR);
+    return mp_obj_new_str_from_vstr(&mp_type_str, &vstr);
 }
 MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_repr_obj, mp_builtin_repr);