[WIP] bpo-17611: Move unwinding of stack from interpreter to compiler

Include/opcode.h

@@ -98,6 +98,7 @@ extern "C" {
 #define END_ITER                117
 #define SETUP_EXCEPT            121
 #define SETUP_FINALLY           122
+#define JUMP_FINALLY            123
 #define LOAD_FAST               124
 #define STORE_FAST              125
 #define DELETE_FAST             126

Lib/opcode.py

@@ -166,6 +166,7 @@ def jabs_op(name, op):
 
 jrel_op('SETUP_EXCEPT', 121)    # Distance to target address
 jrel_op('SETUP_FINALLY', 122)   # ""
+jrel_op('JUMP_FINALLY', 123)    # ""
 
 def_op('LOAD_FAST', 124)        # Local variable number
 haslocal.append(124)

Python/ceval.c

@@ -2075,9 +2075,19 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
             PyObject *exc = POP();
             PyObject *val = POP();
             PyObject *tb = POP();
-            assert(PyExceptionClass_Check(exc));
-            PyErr_Restore(exc, val, tb);
-            goto exception_unwind;
+            if (exc == Py_None) {
+                assert(val == Py_None);
+                assert(tb == Py_None);
+                Py_DECREF(exc);
+                Py_DECREF(val);
+                Py_DECREF(tb);
+            }
+            else {
+                assert(PyExceptionClass_Check(exc));
+                PyErr_Restore(exc, val, tb);
+                goto exception_unwind;
+            }
+            FAST_DISPATCH();
         }
 
         TARGET(LOAD_BUILD_CLASS) {
@@ -2844,6 +2854,18 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
             FAST_DISPATCH();
         }
 
+        TARGET(JUMP_FINALLY) {
+            PyObject *exc = Py_None;
+            Py_INCREF(exc);
+            Py_INCREF(exc);
+            Py_INCREF(exc);
+            PUSH(exc);
+            PUSH(exc);
+            PUSH(exc);
+            JUMPBY(oparg);
+            FAST_DISPATCH();
+        }
+
         PREDICTED(POP_JUMP_IF_FALSE);
         TARGET(POP_JUMP_IF_FALSE) {
             PyObject *cond = POP();

Python/compile.c

@@ -1080,6 +1080,8 @@ PyCompile_OpcodeStackEffect(int opcode, int oparg)
             return (oparg & FVS_MASK) == FVS_HAVE_SPEC ? -1 : 0;
         case LOAD_METHOD:
             return 1;
+        case JUMP_FINALLY:
+            return 3;
         default:
             return PY_INVALID_STACK_EFFECT;
     }
@@ -2695,10 +2697,10 @@ compiler_try_finally(struct compiler *c, stmt_ty s)
     int save_u_lineno_set;
 
     body = compiler_new_block(c);
-    final1 = compiler_new_block(c);
+//     final1 = compiler_new_block(c);
     final2 = compiler_new_block(c);
     exit = compiler_new_block(c);
-    if (body == NULL || final1 == NULL || final2 == NULL || exit == NULL)
+    if (body == NULL || /*final1 == NULL || */final2 == NULL || exit == NULL)
         return 0;
 
     ADDOP_JREL(c, SETUP_FINALLY, final2);
@@ -2713,19 +2715,20 @@ compiler_try_finally(struct compiler *c, stmt_ty s)
         VISIT_SEQ(c, stmt, s->v.Try.body);
     }
     ADDOP(c, POP_BLOCK);
+    ADDOP_JREL(c, JUMP_FINALLY, final2);
     compiler_pop_fblock(c, FINALLY_TRY, body);
     save_u_lineno_set = c->u->u_lineno_set;
 
     /* `finally` block for successful outcome */
-    compiler_use_next_block(c, final1);
-    if (!compiler_push_finally_end(c, final1))
-        return 0;
-    c->u->u_lineno_set = 0;
-    VISIT_SEQ(c, stmt, s->v.Try.finalbody);
-    compiler_pop_fblock(c, FINALLY_END, final1);
-
-    c->u->u_lineno_set = save_u_lineno_set;
-    ADDOP_JABS(c, JUMP_ABSOLUTE, exit);
+//     compiler_use_next_block(c, final1);
+//     if (!compiler_push_finally_end(c, final1))
+//         return 0;
+//     c->u->u_lineno_set = 0;
+//     VISIT_SEQ(c, stmt, s->v.Try.finalbody);
+//     compiler_pop_fblock(c, FINALLY_END, final1);
+//
+//     c->u->u_lineno_set = save_u_lineno_set;
+//     ADDOP_JABS(c, JUMP_ABSOLUTE, exit);
 
     /* `finally` block for exceptional outcome */
     compiler_use_next_block(c, final2);

Python/opcode_targets.h

@@ -122,7 +122,7 @@ static void *opcode_targets[256] = {
     &&_unknown_opcode,
     &&TARGET_SETUP_EXCEPT,
     &&TARGET_SETUP_FINALLY,
-    &&_unknown_opcode,
+    &&TARGET_JUMP_FINALLY,
     &&TARGET_LOAD_FAST,
     &&TARGET_STORE_FAST,
     &&TARGET_DELETE_FAST,

Python/peephole.c

@@ -10,7 +10,8 @@
 #include "opcode.h"
 #include "wordcode_helpers.h"
 
-#define UNCONDITIONAL_JUMP(op)  (op==JUMP_ABSOLUTE || op==END_ITER || op==JUMP_FORWARD)
+#define UNCONDITIONAL_JUMP(op)  (op==JUMP_ABSOLUTE || op==END_ITER || \
+                                 op==JUMP_FORWARD || op==JUMP_FINALLY)
 #define CONDITIONAL_JUMP(op) (op==POP_JUMP_IF_FALSE || op==POP_JUMP_IF_TRUE \
     || op==JUMP_IF_FALSE_OR_POP || op==JUMP_IF_TRUE_OR_POP)
 #define ABSOLUTE_JUMP(op) (op==JUMP_ABSOLUTE || op==END_ITER \
@@ -383,6 +384,7 @@ markblocks(_Py_CODEUNIT *code, Py_ssize_t len)
         switch (opcode) {
             case FOR_ITER:
             case JUMP_FORWARD:
+            case JUMP_FINALLY:
             case JUMP_IF_FALSE_OR_POP:
             case JUMP_IF_TRUE_OR_POP:
             case POP_JUMP_IF_FALSE:
@@ -745,6 +747,7 @@ PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names,
 
             case FOR_ITER:
             case JUMP_FORWARD:
+            case JUMP_FINALLY:
             case SETUP_EXCEPT:
             case SETUP_FINALLY:
                 j = blocks[j / sizeof(_Py_CODEUNIT) + i + 1] - blocks[i] - 1;