gh-92228: disable the compiler's 'small exit block inlining' optimization for blocks...

Inlining of code that corresponds to source code lines, can make it hard to distinguish later between code which is only reachable from except handlers, and that which is reachable in normal control flow. This caused problems with the debugger's jump feature.

This PR turns off the inlining optimisation for code which has line numbers. We still inline things like the implicit "return None".

diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index 256004855d4a6e2dcea833b641fcc58dbeffccdb..440e4ed5eacfb0b0197a6f1e8810ab7cac973860 100644 (file)
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -360,13 +360,13 @@ dis_traceback = """\
     -->    BINARY_OP               11 (/)
            POP_TOP
 
-%3d        LOAD_FAST_CHECK          1 (tb)
+%3d     >> LOAD_FAST_CHECK          1 (tb)
            RETURN_VALUE
         >> PUSH_EXC_INFO
 
 %3d        LOAD_GLOBAL              0 (Exception)
            CHECK_EXC_MATCH
-           POP_JUMP_FORWARD_IF_FALSE    23 (to 82)
+           POP_JUMP_FORWARD_IF_FALSE    22 (to 80)
            STORE_FAST               0 (e)
 
 %3d        LOAD_FAST                0 (e)
@@ -376,9 +376,7 @@ dis_traceback = """\
            LOAD_CONST               0 (None)
            STORE_FAST               0 (e)
            DELETE_FAST              0 (e)
-
-%3d        LOAD_FAST                1 (tb)
-           RETURN_VALUE
+           JUMP_BACKWARD           29 (to 14)
         >> LOAD_CONST               0 (None)
            STORE_FAST               0 (e)
            DELETE_FAST              0 (e)
@@ -396,7 +394,6 @@ ExceptionTable:
        TRACEBACK_CODE.co_firstlineno + 5,
        TRACEBACK_CODE.co_firstlineno + 3,
        TRACEBACK_CODE.co_firstlineno + 4,
-       TRACEBACK_CODE.co_firstlineno + 5,
        TRACEBACK_CODE.co_firstlineno + 3)
 
 def _fstring(a, b, c, d):
@@ -443,7 +440,7 @@ dis_with = """\
            CALL                     2
            POP_TOP
 
-%3d        LOAD_CONST               2 (2)
+%3d     >> LOAD_CONST               2 (2)
            STORE_FAST               2 (y)
            LOAD_CONST               0 (None)
            RETURN_VALUE
@@ -456,11 +453,7 @@ dis_with = """\
            POP_EXCEPT
            POP_TOP
            POP_TOP
-
-%3d        LOAD_CONST               2 (2)
-           STORE_FAST               2 (y)
-           LOAD_CONST               0 (None)
-           RETURN_VALUE
+           JUMP_BACKWARD           13 (to 30)
         >> COPY                     3
            POP_EXCEPT
            RERAISE                  1
@@ -472,7 +465,6 @@ ExceptionTable:
        _with.__code__.co_firstlineno + 1,
        _with.__code__.co_firstlineno + 3,
        _with.__code__.co_firstlineno + 1,
-       _with.__code__.co_firstlineno + 3,
        )
 
 async def _asyncwith(c):
@@ -510,7 +502,7 @@ dis_asyncwith = """\
            JUMP_BACKWARD_NO_INTERRUPT     4 (to 48)
         >> POP_TOP
 
-%3d        LOAD_CONST               2 (2)
+%3d     >> LOAD_CONST               2 (2)
            STORE_FAST               2 (y)
            LOAD_CONST               0 (None)
            RETURN_VALUE
@@ -529,11 +521,7 @@ dis_asyncwith = """\
            POP_EXCEPT
            POP_TOP
            POP_TOP
-
-%3d        LOAD_CONST               2 (2)
-           STORE_FAST               2 (y)
-           LOAD_CONST               0 (None)
-           RETURN_VALUE
+           JUMP_BACKWARD           19 (to 58)
         >> COPY                     3
            POP_EXCEPT
            RERAISE                  1
@@ -545,7 +533,6 @@ ExceptionTable:
        _asyncwith.__code__.co_firstlineno + 1,
        _asyncwith.__code__.co_firstlineno + 3,
        _asyncwith.__code__.co_firstlineno + 1,
-       _asyncwith.__code__.co_firstlineno + 3,
        )
 
 

diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
index 2c3b1ab65a8f9d834620407635dd4551eefe0478..e03c42c2f823dc8241be1ba3e95b895b633b4888 100644 (file)
--- a/Lib/test/test_peepholer.py
+++ b/Lib/test/test_peepholer.py
@@ -345,6 +345,8 @@ class TestTranforms(BytecodeTestCase):
         self.assertEqual(len(returns), 1)
         self.check_lnotab(f)
 
+    @unittest.skip("Following gh-92228 the return has two predecessors "
+                   "and that prevents jump elimination.")
     def test_elim_jump_to_return(self):
         # JUMP_FORWARD to RETURN -->  RETURN
         def f(cond, true_value, false_value):

diff --git a/Lib/test/test_sys_settrace.py b/Lib/test/test_sys_settrace.py
index 7ec290dbf04ad50a88d30325b3b069e593345d52..f03b03e19a2528b3ffc1472cd30d91c223fba1df 100644 (file)
--- a/Lib/test/test_sys_settrace.py
+++ b/Lib/test/test_sys_settrace.py
@@ -2042,6 +2042,15 @@ class JumpTestCase(unittest.TestCase):
             output.append(6)
         output.append(7)
 
+    @jump_test(6, 1, [1, 5, 1, 5])
+    def test_jump_over_try_except(output):
+        output.append(1)
+        try:
+            1 / 0
+        except ZeroDivisionError as e:
+            output.append(5)
+        x = 42  # has to be a two-instruction block
+
     @jump_test(2, 4, [1, 4, 5, -4])
     def test_jump_across_with(output):
         output.append(1)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-07-06-14-02-26.gh-issue-92228.44Cbly.rst b/Misc/NEWS.d/next/Core and Builtins/2022-07-06-14-02-26.gh-issue-92228.44Cbly.rst
new file mode 100644 (file)
index 0000000..458ad89
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-07-06-14-02-26.gh-issue-92228.44Cbly.rst
@@ -0,0 +1 @@
+Disable the compiler's inline-small-exit-blocks optimization for exit blocks that are associated with source code lines. This fixes a bug where the debugger cannot tell where an exception handler ends and the following code block begins.

diff --git a/Python/compile.c b/Python/compile.c
index 77176893f60c5cc91215107f1265d6ec4e80a697..f36a6e85a54c20b4f80d38333865d459b5ffa12a 100644 (file)
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -9224,6 +9224,16 @@ error:
     return -1;
 }
 
+static bool
+basicblock_has_lineno(const basicblock *bb) {
+    for (int i = 0; i < bb->b_iused; i++) {
+        if (bb->b_instr[i].i_loc.lineno > 0) {
+            return true;
+        }
+    }
+    return false;
+}
+
 /* If this block ends with an unconditional jump to an exit block,
  * then remove the jump and extend this block with the target.
  */
@@ -9240,6 +9250,10 @@ extend_block(basicblock *bb) {
     }
     if (basicblock_exits_scope(last->i_target) && last->i_target->b_iused <= MAX_COPY_SIZE) {
         basicblock *to_copy = last->i_target;
+        if (basicblock_has_lineno(to_copy)) {
+            /* copy only blocks without line number (like implicit 'return None's) */
+            return 0;
+        }
         last->i_opcode = NOP;
         for (int i = 0; i < to_copy->b_iused; i++) {
             int index = basicblock_next_instr(bb);