py: Remove mp_obj_str_builder and use vstr instead.

With this patch str/bytes construction is streamlined.  Always use a
vstr to build a str/bytes object.  If the size is known beforehand then
use vstr_init_len to allocate only required memory.  Otherwise use
vstr_init and the vstr will grow as needed.  Then use
mp_obj_new_str_from_vstr to create a str/bytes object using the vstr
memory.

Saves code ROM: 68 bytes on stmhal, 108 bytes on bare-arm, and 336 bytes
on unix x64.

1 files changed, 8 insertions, 6 deletions

diff --git a/stmhal/bufhelper.c b/stmhal/bufhelper.c
index 57aef5a91e..ca76e9496d 100644
--- a/stmhal/bufhelper.c
+++ b/stmhal/bufhelper.c
@@ -38,15 +38,17 @@ void pyb_buf_get_for_send(mp_obj_t o, mp_buffer_info_t *bufinfo, byte *tmp_data)
     }
 }
 
-mp_obj_t pyb_buf_get_for_recv(mp_obj_t o, mp_buffer_info_t *bufinfo) {
+mp_obj_t pyb_buf_get_for_recv(mp_obj_t o, vstr_t *vstr) {
     if (MP_OBJ_IS_INT(o)) {
         // allocate a new bytearray of given length
-        bufinfo->len = mp_obj_get_int(o);
-        bufinfo->typecode = 'B';
-        return mp_obj_str_builder_start(&mp_type_bytes, bufinfo->len, (byte**)&bufinfo->buf);
+        vstr_init_len(vstr, mp_obj_get_int(o));
+        return MP_OBJ_NULL;
     } else {
         // get the existing buffer
-        mp_get_buffer_raise(o, bufinfo, MP_BUFFER_WRITE);
-        return MP_OBJ_NULL;
+        mp_buffer_info_t bufinfo;
+        mp_get_buffer_raise(o, &bufinfo, MP_BUFFER_WRITE);
+        vstr->buf = bufinfo.buf;
+        vstr->len = bufinfo.len;
+        return o;
     }
 }