GH-93621: reorder code in with/async-with exception exit path to reduce the size of the exception table (GH-93622)

Lib/test/test_dis.py

@@ -389,6 +389,7 @@ dis_traceback = """\
            POP_EXCEPT
            RERAISE                  1
 ExceptionTable:
+4 rows
 """ % (TRACEBACK_CODE.co_firstlineno,
        TRACEBACK_CODE.co_firstlineno + 1,
        TRACEBACK_CODE.co_firstlineno + 2,
@@ -421,6 +422,133 @@ dis_fstring = """\
            RETURN_VALUE
 """ % (_fstring.__code__.co_firstlineno, _fstring.__code__.co_firstlineno + 1)
 
+def _with(c):
+    with c:
+        x = 1
+    y = 2
+
+dis_with = """\
+%3d        RESUME                   0
+
+%3d        LOAD_FAST                0 (c)
+           BEFORE_WITH
+           POP_TOP
+
+%3d        LOAD_CONST               1 (1)
+           STORE_FAST               1 (x)
+
+%3d        LOAD_CONST               0 (None)
+           LOAD_CONST               0 (None)
+           LOAD_CONST               0 (None)
+           CALL                     2
+           POP_TOP
+
+%3d        LOAD_CONST               2 (2)
+           STORE_FAST               2 (y)
+           LOAD_CONST               0 (None)
+           RETURN_VALUE
+
+%3d     >> PUSH_EXC_INFO
+           WITH_EXCEPT_START
+           POP_JUMP_FORWARD_IF_TRUE     1 (to 46)
+           RERAISE                  2
+        >> POP_TOP
+           POP_EXCEPT
+           POP_TOP
+           POP_TOP
+
+%3d        LOAD_CONST               2 (2)
+           STORE_FAST               2 (y)
+           LOAD_CONST               0 (None)
+           RETURN_VALUE
+        >> COPY                     3
+           POP_EXCEPT
+           RERAISE                  1
+ExceptionTable:
+2 rows
+""" % (_with.__code__.co_firstlineno,
+       _with.__code__.co_firstlineno + 1,
+       _with.__code__.co_firstlineno + 2,
+       _with.__code__.co_firstlineno + 1,
+       _with.__code__.co_firstlineno + 3,
+       _with.__code__.co_firstlineno + 1,
+       _with.__code__.co_firstlineno + 3,
+       )
+
+async def _asyncwith(c):
+    async with c:
+        x = 1
+    y = 2
+
+dis_asyncwith = """\
+%3d        RETURN_GENERATOR
+           POP_TOP
+           RESUME                   0
+
+%3d        LOAD_FAST                0 (c)
+           BEFORE_ASYNC_WITH
+           GET_AWAITABLE            1
+           LOAD_CONST               0 (None)
+        >> SEND                     3 (to 22)
+           YIELD_VALUE              3
+           RESUME                   3
+           JUMP_BACKWARD_NO_INTERRUPT     4 (to 14)
+        >> POP_TOP
+
+%3d        LOAD_CONST               1 (1)
+           STORE_FAST               1 (x)
+
+%3d        LOAD_CONST               0 (None)
+           LOAD_CONST               0 (None)
+           LOAD_CONST               0 (None)
+           CALL                     2
+           GET_AWAITABLE            2
+           LOAD_CONST               0 (None)
+        >> SEND                     3 (to 56)
+           YIELD_VALUE              2
+           RESUME                   3
+           JUMP_BACKWARD_NO_INTERRUPT     4 (to 48)
+        >> POP_TOP
+
+%3d        LOAD_CONST               2 (2)
+           STORE_FAST               2 (y)
+           LOAD_CONST               0 (None)
+           RETURN_VALUE
+
+%3d     >> PUSH_EXC_INFO
+           WITH_EXCEPT_START
+           GET_AWAITABLE            2
+           LOAD_CONST               0 (None)
+        >> SEND                     3 (to 82)
+           YIELD_VALUE              6
+           RESUME                   3
+           JUMP_BACKWARD_NO_INTERRUPT     4 (to 74)
+        >> POP_JUMP_FORWARD_IF_TRUE     1 (to 86)
+           RERAISE                  2
+        >> POP_TOP
+           POP_EXCEPT
+           POP_TOP
+           POP_TOP
+
+%3d        LOAD_CONST               2 (2)
+           STORE_FAST               2 (y)
+           LOAD_CONST               0 (None)
+           RETURN_VALUE
+        >> COPY                     3
+           POP_EXCEPT
+           RERAISE                  1
+ExceptionTable:
+2 rows
+""" % (_asyncwith.__code__.co_firstlineno,
+       _asyncwith.__code__.co_firstlineno + 1,
+       _asyncwith.__code__.co_firstlineno + 2,
+       _asyncwith.__code__.co_firstlineno + 1,
+       _asyncwith.__code__.co_firstlineno + 3,
+       _asyncwith.__code__.co_firstlineno + 1,
+       _asyncwith.__code__.co_firstlineno + 3,
+       )
+
+
 def _tryfinally(a, b):
     try:
         return a
@@ -455,6 +583,7 @@ dis_tryfinally = """\
            POP_EXCEPT
            RERAISE                  1
 ExceptionTable:
+2 rows
 """ % (_tryfinally.__code__.co_firstlineno,
        _tryfinally.__code__.co_firstlineno + 1,
        _tryfinally.__code__.co_firstlineno + 2,
@@ -484,6 +613,7 @@ dis_tryfinallyconst = """\
            POP_EXCEPT
            RERAISE                  1
 ExceptionTable:
+1 row
 """ % (_tryfinallyconst.__code__.co_firstlineno,
        _tryfinallyconst.__code__.co_firstlineno + 1,
        _tryfinallyconst.__code__.co_firstlineno + 2,
@@ -678,6 +808,18 @@ class DisTestBase(unittest.TestCase):
             self.assertGreaterEqual(offset, expected_offset, line)
             expected_offset = offset + delta
 
+    def assert_exception_table_increasing(self, lines):
+        prev_start, prev_end = -1, -1
+        count = 0
+        for line in lines:
+            m = re.match(r'  (\d+) to (\d+) -> \d+ \[\d+\]', line)
+            start, end = [int(g) for g in m.groups()]
+            self.assertGreaterEqual(end, start)
+            self.assertGreater(start, prev_end)
+            prev_start, prev_end = start, end
+            count += 1
+        return count
+
     def strip_offsets(self, text):
         lines = text.splitlines(True)
         start, end = self.find_offset_column(lines)
@@ -691,6 +833,9 @@ class DisTestBase(unittest.TestCase):
                 res.append(line)
             else:
                 res.append(line[:start] + line[end:])
+        num_rows = self.assert_exception_table_increasing(lines)
+        if num_rows:
+            res.append(f"{num_rows} row{'s' if num_rows > 1 else ''}\n")
         return "".join(res)
 
     def do_disassembly_compare(self, got, expected, with_offsets=False):
@@ -883,6 +1028,12 @@ class DisTests(DisTestBase):
     def test_disassemble_fstring(self):
         self.do_disassembly_test(_fstring, dis_fstring)
 
+    def test_disassemble_with(self):
+        self.do_disassembly_test(_with, dis_with)
+
+    def test_disassemble_asyncwith(self):
+        self.do_disassembly_test(_asyncwith, dis_asyncwith)
+
     def test_disassemble_try_finally(self):
         self.do_disassembly_test(_tryfinally, dis_tryfinally)
         self.do_disassembly_test(_tryfinallyconst, dis_tryfinallyconst)
@@ -1471,16 +1622,16 @@ expected_opinfo_jumpy = [
   Instruction(opname='RETURN_VALUE', opcode=83, arg=None, argval=None, argrepr='', offset=302, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='PUSH_EXC_INFO', opcode=35, arg=None, argval=None, argrepr='', offset=304, starts_line=25, is_jump_target=False, positions=None),
   Instruction(opname='WITH_EXCEPT_START', opcode=49, arg=None, argval=None, argrepr='', offset=306, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='POP_JUMP_FORWARD_IF_TRUE', opcode=115, arg=4, argval=318, argrepr='to 318', offset=308, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='POP_JUMP_FORWARD_IF_TRUE', opcode=115, arg=1, argval=312, argrepr='to 312', offset=308, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='RERAISE', opcode=119, arg=2, argval=2, argrepr='', offset=310, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='COPY', opcode=120, arg=3, argval=3, argrepr='', offset=312, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=312, starts_line=None, is_jump_target=True, positions=None),
   Instruction(opname='POP_EXCEPT', opcode=89, arg=None, argval=None, argrepr='', offset=314, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='RERAISE', opcode=119, arg=1, argval=1, argrepr='', offset=316, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=316, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=318, starts_line=None, is_jump_target=True, positions=None),
+  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=318, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='POP_EXCEPT', opcode=89, arg=None, argval=None, argrepr='', offset=320, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='JUMP_BACKWARD', opcode=140, arg=24, argval=274, argrepr='to 274', offset=320, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=322, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='COPY', opcode=120, arg=3, argval=3, argrepr='', offset=322, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=324, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='POP_EXCEPT', opcode=89, arg=None, argval=None, argrepr='', offset=324, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='JUMP_BACKWARD', opcode=140, arg=27, argval=274, argrepr='to 274', offset=326, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='RERAISE', opcode=119, arg=1, argval=1, argrepr='', offset=326, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='PUSH_EXC_INFO', opcode=35, arg=None, argval=None, argrepr='', offset=328, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=4, argval='ZeroDivisionError', argrepr='ZeroDivisionError', offset=330, starts_line=22, is_jump_target=False, positions=None),
   Instruction(opname='CHECK_EXC_MATCH', opcode=36, arg=None, argval=None, argrepr='', offset=342, starts_line=None, is_jump_target=False, positions=None),

Misc/NEWS.d/next/Core and Builtins/2022-06-09-09-08-29.gh-issue-93621.-_Pn1d.rst

@@ -0,0 +1 @@
+Change order of bytecode instructions emitted for :keyword:`with` and :keyword:`async with` to reduce the number of entries in the exception table.

Python/compile.c

@@ -5551,20 +5551,26 @@ compiler_visit_keyword(struct compiler *c, keyword_ty k)
 static int
 compiler_with_except_finish(struct compiler *c, basicblock * cleanup) {
     UNSET_LOC(c);
-    basicblock *exit;
+    basicblock *suppress = compiler_new_block(c);
-    exit = compiler_new_block(c);
+    if (suppress == NULL) {
-    if (exit == NULL)
         return 0;
-    ADDOP_JUMP(c, POP_JUMP_IF_TRUE, exit);
+    }
+    ADDOP_JUMP(c, POP_JUMP_IF_TRUE, suppress);
     ADDOP_I(c, RERAISE, 2);
-    compiler_use_next_block(c, cleanup);
+    compiler_use_next_block(c, suppress);
-    POP_EXCEPT_AND_RERAISE(c);
-    compiler_use_next_block(c, exit);
     ADDOP(c, POP_TOP); /* exc_value */
     ADDOP(c, POP_BLOCK);
     ADDOP(c, POP_EXCEPT);
     ADDOP(c, POP_TOP);
     ADDOP(c, POP_TOP);
+    basicblock *exit = compiler_new_block(c);
+    if (exit == NULL) {
+        return 0;
+    }
+    ADDOP_JUMP(c, JUMP, exit);
+    compiler_use_next_block(c, cleanup);
+    POP_EXCEPT_AND_RERAISE(c);
+    compiler_use_next_block(c, exit);
     return 1;
 }