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gh-133371: Don't optimize LOAD_FAST instructions whose local is killed by DELETE_FAST#133383

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Merged
mpage merged 4 commits into from
May 5, 2025
Merged

gh-133371: Don't optimize LOAD_FAST instructions whose local is killed by DELETE_FAST#133383

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b78eb39
Don't optimize `LOAD_FAST` instructions whose local is killed by `DEL…
mpage May 4, 2025
e1182c7
Bump the magic number
mpage May 5, 2025
193c16c
Add minimal repro of crash as a test
mpage May 5, 2025
09e834c
Merge branch 'main' into gh-133371-handle-del-fast
mpage May 5, 2025
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3 changes: 2 additions & 1 deletion Include/internal/pycore_magic_number.h
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Original file line numberDiff line numberDiff line change
Expand Up@@ -276,6 +276,7 @@ Known values:
Python 3.14a7 3621 (Optimize LOAD_FAST opcodes into LOAD_FAST_BORROW)
Python 3.14a7 3622 (Store annotations in different class dict keys)
Python 3.14a7 3623 (Add BUILD_INTERPOLATION & BUILD_TEMPLATE opcodes)
Python 3.14b1 3624 (Don't optimize LOAD_FAST when local is killed by DELETE_FAST)

Python 3.15 will start with 3650

Expand All@@ -288,7 +289,7 @@ PC/launcher.c must also be updated.

*/

#define PYC_MAGIC_NUMBER 3623
#define PYC_MAGIC_NUMBER 3624
/* This is equivalent to converting PYC_MAGIC_NUMBER to 2 bytes
(little-endian) and then appending b'\r\n'. */
#define PYC_MAGIC_NUMBER_TOKEN \
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24 changes: 24 additions & 0 deletions Lib/test/test_peepholer.py
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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
import dis
import gc
from itertools import combinations, product
import opcode
import sys
Expand DownExpand Up@@ -2472,6 +2473,13 @@ def test_unoptimized_if_support_killed(self):
]
self.check(insts, insts)

insts = [
("LOAD_FAST", 0, 1),
("DELETE_FAST", 0, 2),
("POP_TOP", None, 3),
]
self.check(insts, insts)

def test_unoptimized_if_aliased(self):
insts = [
("LOAD_FAST", 0, 1),
Expand DownExpand Up@@ -2606,6 +2614,22 @@ def test_send(self):
]
self.cfg_optimization_test(insts, expected, consts=[None])

def test_del_in_finally(self):
# This loads `obj` onto the stack, executes `del obj`, then returns the
# `obj` from the stack. See gh-133371 for more details.
def create_obj():
obj = [42]
try:
return obj
finally:
del obj

obj = create_obj()
# The crash in the linked issue happens while running GC during
# interpreter finalization, so run it here manually.
gc.collect()
self.assertEqual(obj, [42])



if __name__ == "__main__":
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5 changes: 5 additions & 0 deletions Python/flowgraph.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -2795,6 +2795,11 @@ optimize_load_fast(cfg_builder *g)
assert(opcode != EXTENDED_ARG);
switch (opcode){
// Opcodes that load and store locals
case DELETE_FAST:{
kill_local(instr_flags, &refs, oparg);
break;
}

Comment on lines +2798 to +2802
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@gvanrossumgvanrossumMay 4, 2025

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FWIW: This change by itself is not enough to make the crash in test_asyncio go away.

case LOAD_FAST:{
PUSH_REF(i, oparg);
break;
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