py: Properly implement deletion of locals and derefs, and detect errors.

Needed to reinstate 2 delete opcodes, to specifically check that a local
is not deleted twice.

1 files changed, 14 insertions, 10 deletions

diff --git a/py/emitbc.c b/py/emitbc.c
index f16ffced11..21d1a61863 100644
--- a/py/emitbc.c
+++ b/py/emitbc.c
@@ -408,14 +408,20 @@ STATIC void emit_bc_load_null(emit_t *emit) {
     emit_write_byte_code_byte(emit, MP_BC_LOAD_NULL);
 };
 
-STATIC void emit_bc_load_fast(emit_t *emit, qstr qstr, int local_num) {
+STATIC void emit_bc_load_fast(emit_t *emit, qstr qstr, uint id_flags, int local_num) {
     assert(local_num >= 0);
     emit_bc_pre(emit, 1);
-    switch (local_num) {
-        case 0: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_0); break;
-        case 1: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_1); break;
-        case 2: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_2); break;
-        default: emit_write_byte_code_byte_uint(emit, MP_BC_LOAD_FAST_N, local_num); break;
+    if (id_flags & ID_FLAG_IS_DELETED) {
+        // This local may be deleted, so need to do a checked load.
+        emit_write_byte_code_byte_uint(emit, MP_BC_LOAD_FAST_CHECKED, local_num);
+    } else {
+        // This local is never deleted, so can do a fast, uncheched load.
+        switch (local_num) {
+            case 0: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_0); break;
+            case 1: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_1); break;
+            case 2: emit_write_byte_code_byte(emit, MP_BC_LOAD_FAST_2); break;
+            default: emit_write_byte_code_byte_uint(emit, MP_BC_LOAD_FAST_N, local_num); break;
+        }
     }
 }
 
@@ -491,13 +497,11 @@ STATIC void emit_bc_store_subscr(emit_t *emit) {
 }
 
 STATIC void emit_bc_delete_fast(emit_t *emit, qstr qstr, int local_num) {
-    emit_bc_load_null(emit);
-    emit_bc_store_fast(emit, qstr, local_num);
+    emit_write_byte_code_byte_uint(emit, MP_BC_DELETE_FAST, local_num);
 }
 
 STATIC void emit_bc_delete_deref(emit_t *emit, qstr qstr, int local_num) {
-    emit_bc_load_null(emit);
-    emit_bc_store_deref(emit, qstr, local_num);
+    emit_write_byte_code_byte_uint(emit, MP_BC_DELETE_DEREF, local_num);
 }
 
 STATIC void emit_bc_delete_name(emit_t *emit, qstr qstr) {