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gh-92228: disable the compiler's 'small exit block inlining' optimization for blocks that have a line number (GH-94592)

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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".
This commit is contained in:
Irit Katriel 2022-07-07 07:38:36 +01:00 committed by GitHub
parent 94988603f3
commit bde06e1b83
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GPG Key ID: 4AEE18F83AFDEB23
5 changed files with 33 additions and 20 deletions
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27
Lib/test/test_dis.py
View File

@ -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,
)

2
Lib/test/test_peepholer.py
View File

@ -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):

9
Lib/test/test_sys_settrace.py
View File

@ -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)

1
Misc/NEWS.d/next/Core and Builtins/2022-07-06-14-02-26.gh-issue-92228.44Cbly.rst Normal file
View File

@ -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.

14
Python/compile.c
View File

@ -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);