FazBrowse GitHub Viewer | Trending |
URL:
| Home
Tools: [Download Repo ZIP]   [Original HTTPS Page]

gh-133672: Allow LOAD_FAST to be optimized to LOAD_FAST_BORROW by ljfp · Pull Request #148999 · python/cpython · GitHub

/ cpython Public

gh-133672: Allow LOAD_FAST to be optimized to LOAD_FAST_BORROW #148999

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ljfp wants to merge 2 commits into
base: main
Choose a base branch
Could not load branches
Branch not found: {{ refName }}

Are you sure you want to change the base?

Some commits from the old base branch may be removed from the timeline, and old review comments may become outdated.
from
+546 −12
Conversation 2 Commits 2 Checks 51 Files changed 4
Open

gh-133672: Allow LOAD_FAST to be optimized to LOAD_FAST_BORROW #148999

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
08238d2
gh-133672: Allow LOAD_FAST to be optimized to LOAD_FAST_BORROW
ljfp Apr 25, 2026
28d06a6
Merge branch 'main' into fix-issue-133672
ljfp May 14, 2026
File filter

Filter by extension

Filter by extension .c  (1) .py  (2) .rst  (1) All 3 file types selected
Viewed files
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Unified
Split
Hide whitespace
Diff view
Unified
Split
Hide whitespace
4 changes: 2 additions & 2 deletions Lib/test/test_dis.py
Show comments
View file
Open in desktop
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
Show hidden characters
Original file line number Diff line number Diff line change
Expand Up @@ -542,7 +542,7 @@ def _with(c):
dis_with = """\
%4d RESUME 0

%4d LOAD_FAST_BORROW 0 (c)
%4d LOAD_FAST 0 (c)
COPY 1
LOAD_SPECIAL 1 (__exit__)
SWAP 2
Expand Down Expand Up @@ -1919,7 +1919,7 @@ def _prepare_test_cases():
make_inst(opname='LOAD_SMALL_INT', arg=0, argval=0, argrepr='', offset=244, start_offset=244, starts_line=False, line_number=21),
make_inst(opname='BINARY_OP', arg=11, argval=11, argrepr='/', offset=246, start_offset=246, starts_line=False, line_number=21, cache_info=[('counter', 1, b'\x00\x00'), ('descr', 4, b'\x00\x00\x00\x00\x00\x00\x00\x00')]),
make_inst(opname='POP_TOP', arg=None, argval=None, argrepr='', offset=258, start_offset=258, starts_line=False, line_number=21),
make_inst(opname='LOAD_FAST_BORROW', arg=0, argval='i', argrepr='i', offset=260, start_offset=260, starts_line=True, line_number=25),
make_inst(opname='LOAD_FAST', arg=0, argval='i', argrepr='i', offset=260, start_offset=260, starts_line=True, line_number=25),
make_inst(opname='COPY', arg=1, argval=1, argrepr='', offset=262, start_offset=262, starts_line=False, line_number=25),
make_inst(opname='LOAD_SPECIAL', arg=1, argval=1, argrepr='__exit__', offset=264, start_offset=264, starts_line=False, line_number=25),
make_inst(opname='SWAP', arg=2, argval=2, argrepr='', offset=266, start_offset=266, starts_line=False, line_number=25),
Expand Down
98 changes: 97 additions & 1 deletion Lib/test/test_peepholer.py
Show comments
View file
Open in desktop
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
Show hidden characters
Original file line number Diff line number Diff line change
Expand Up @@ -2643,7 +2643,7 @@ def test_for_iter(self):
("RETURN_VALUE", None, 8),
]
expected = [
("LOAD_FAST", 0, 1),
("LOAD_FAST_BORROW", 0, 1),
top := self.Label(),
("FOR_ITER", end := self.Label(), 2),
("STORE_FAST", 2, 3),
Expand All @@ -2656,6 +2656,39 @@ def test_for_iter(self):
]
self.cfg_optimization_test(insts, expected, consts=[None])

def test_for_iter_checks_fallthrough(self):
insts = [
("LOAD_FAST", 0, 1),
("GET_ITER", 0, 2),
top := self.Label(),
("FOR_ITER", end := self.Label(), 3),
("STORE_FAST", 1, 4),
("LOAD_CONST", 0, 5),
("STORE_FAST", 0, 6),
("JUMP", top, 7),
end,
("END_FOR", None, 8),
("POP_ITER", None, 9),
("LOAD_CONST", 0, 10),
("RETURN_VALUE", None, 11),
]
expected = [
("LOAD_FAST", 0, 1),
("GET_ITER", 0, 2),
top := self.Label(),
("FOR_ITER", end := self.Label(), 3),
("STORE_FAST", 1, 4),
("LOAD_COMMON_CONSTANT", 7, 5),
("STORE_FAST", 0, 6),
("JUMP", top, 7),
end,
("END_FOR", None, 8),
("POP_ITER", None, 9),
("LOAD_COMMON_CONSTANT", 7, 10),
("RETURN_VALUE", None, 11),
]
self.cfg_optimization_test(insts, expected, consts=[None])

def test_load_attr(self):
insts = [
("LOAD_FAST", 0, 1),
Expand Down Expand Up @@ -2731,6 +2764,69 @@ def test_send(self):
]
self.cfg_optimization_test(insts, expected, consts=[None])

def test_borrow_checks_exception_handler_edges(self):
insts = [
("LOAD_FAST", 0, 1),
("JUMP", start := self.Label(), 2),
start,
("SETUP_FINALLY", handler := self.Label(), 3),
("LOAD_CONST", 0, 4),
("BINARY_OP", 0, 5),
("POP_BLOCK", None, 6),
("RETURN_VALUE", None, 7),
handler,
("STORE_FAST", 1, 8),
("LOAD_CONST", 0, 9),
("STORE_FAST", 0, 10),
("POP_TOP", None, 11),
("LOAD_CONST", 0, 12),
("RETURN_VALUE", None, 13),
]
expected = [
("LOAD_FAST", 0, 1),
("NOP", None, 2),
("SETUP_FINALLY", handler := self.Label(), 3),
("LOAD_COMMON_CONSTANT", 7, 4),
("BINARY_OP", 0, 5),
("NOP", None, 6),
("RETURN_VALUE", None, 7),
handler,
("STORE_FAST", 1, 8),
("LOAD_COMMON_CONSTANT", 7, 9),
("STORE_FAST", 0, 10),
("POP_TOP", None, 11),
("LOAD_COMMON_CONSTANT", 7, 12),
("RETURN_VALUE", None, 13),
]
self.cfg_optimization_test(insts, expected, consts=[None])

def test_copied_reference_is_not_borrowed(self):
insts = [
("LOAD_FAST", 0, 1),
("COPY", 1, 1),
("TO_BOOL", None, 1),
("POP_JUMP_IF_TRUE", target := self.Label(), 1),
("POP_TOP", None, 1),
("LOAD_FAST", 1, 1),
target,
("STORE_FAST", 0, 1),
("LOAD_CONST", 0, 2),
("RETURN_VALUE", None, 2),
]
expected = [
("LOAD_FAST", 0, 1),
("COPY", 1, 1),
("TO_BOOL", None, 1),
("POP_JUMP_IF_TRUE", target := self.Label(), 1),
("POP_TOP", None, 1),
("LOAD_FAST", 1, 1),
target,
("STORE_FAST", 0, 1),
("LOAD_COMMON_CONSTANT", 7, 2),
("RETURN_VALUE", None, 2),
]
self.cfg_optimization_test(insts, expected, consts=[None])

def test_format_simple(self):
# FORMAT_SIMPLE will leave its operand on the stack if it's a unicode
# object. We treat it conservatively and assume that it always leaves
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-05-09-00-06-52.gh-issue-133672.y6QwwH.rst
Show comments
View file
Open in desktop
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
Show hidden characters
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
The peephole optimizer now converts LOAD_FAST to LOAD_FAST_BORROW more aggressively. This optimization is applied even if the loaded variable remains live on the stack at the end of a basic block, as long as the borrow is otherwise determined to be safe. This can reduce reference counting overhead in certain code patterns, such as with iterables in loops.
Loading
Loading
Back | FazBrowse Home | New Git URL