GH-94438: Account for NULLs on evaluation stack when jumping lines. (GH-94444)

1 files changed, 43 insertions, 13 deletions

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 44cc062..34a6c46 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -137,9 +137,24 @@ typedef enum kind {
     Iterator = 1,
     Except = 2,
     Object = 3,
+    Null = 4,
 } Kind;
 
-#define BITS_PER_BLOCK 2
+static int
+compatible_kind(Kind from, Kind to) {
+    if (to == 0) {
+        return 0;
+    }
+    if (to == Object) {
+        return from != Null;
+    }
+    if (to == Null) {
+        return 1;
+    }
+    return from == to;
+}
+
+#define BITS_PER_BLOCK 3
 
 #define UNINITIALIZED -2
 #define OVERFLOWED -1
@@ -298,6 +313,31 @@ mark_stacks(PyCodeObject *code_obj, int len)
                 case RERAISE:
                     /* End of block */
                     break;
+                case PUSH_NULL:
+                    next_stack = push_value(next_stack, Null);
+                    stacks[i+1] = next_stack;
+                    break;
+                case LOAD_GLOBAL:
+                {
+                    int j = get_arg(code, i);
+                    if (j & 1) {
+                        next_stack = push_value(next_stack, Null);
+                    }
+                    next_stack = push_value(next_stack, Object);
+                    stacks[i+1] = next_stack;
+                    break;
+                }
+                case LOAD_ATTR:
+                {
+                    int j = get_arg(code, i);
+                    if (j & 1) {
+                        next_stack = pop_value(next_stack);
+                        next_stack = push_value(next_stack, Null);
+                        next_stack = push_value(next_stack, Object);
+                    }
+                    stacks[i+1] = next_stack;
+                    break;
+                }
                 default:
                 {
                     int delta = PyCompile_OpcodeStackEffect(opcode, _Py_OPARG(code[i]));
@@ -319,17 +359,6 @@ mark_stacks(PyCodeObject *code_obj, int len)
 }
 
 static int
-compatible_kind(Kind from, Kind to) {
-    if (to == 0) {
-        return 0;
-    }
-    if (to == Object) {
-        return 1;
-    }
-    return from == to;
-}
-
-static int
 compatible_stack(int64_t from_stack, int64_t to_stack)
 {
     if (from_stack < 0 || to_stack < 0) {
@@ -365,7 +394,8 @@ explain_incompatible_stack(int64_t to_stack)
         case Except:
             return "can't jump into an 'except' block as there's no exception";
         case Object:
-            return "differing stack depth";
+        case Null:
+            return "incompatible stacks";
         case Iterator:
             return "can't jump into the body of a for loop";
         default: