Brandt Bucher <[email protected]> added the comment:
In practice, pretty much the only thing that will do more work now is augmented
subscription:
>>> a[b] += c
main:
1 2 LOAD_NAME 0 (a)
4 LOAD_NAME 1 (b)
6 DUP_TOP_TWO
8 BINARY_SUBSCR
10 LOAD_NAME 2 (c)
12 BINARY_OP 13 (+=)
14 ROT_THREE
16 STORE_SUBSCR
patched:
1 2 LOAD_NAME 0 (a)
4 LOAD_NAME 1 (b)
6 COPY 2
8 COPY 2
10 BINARY_SUBSCR
12 LOAD_NAME 2 (c)
14 BINARY_OP 13 (+=)
16 SWAP 3
18 SWAP 2
20 STORE_SUBSCR
Pattern matching is the only place where we use ROT_N, and frankly it's
*misused* there... often, it makes the cost of storing names quadratic at
runtime. Even though we emit *more* instructions now, the peephole optimizer
actually cuts them down significantly, and the result is more efficient than
before. For example:
>>> match x:
... case (a, b, c, None):
... pass
main:
1 2 LOAD_NAME 0 (x)
2 4 MATCH_SEQUENCE
6 POP_JUMP_IF_FALSE 20 (to 40)
8 GET_LEN
10 LOAD_CONST 0 (4)
12 COMPARE_OP 2 (==)
14 POP_JUMP_IF_FALSE 20 (to 40)
16 UNPACK_SEQUENCE 4
18 ROT_FOUR
20 ROT_FOUR
22 ROT_FOUR
24 POP_JUMP_IF_NOT_NONE 18 (to 36)
26 STORE_NAME 1 (a)
28 STORE_NAME 2 (b)
30 STORE_NAME 3 (c)
3 32 LOAD_CONST 1 (None)
34 RETURN_VALUE
2 >> 36 POP_TOP
38 POP_TOP
>> 40 POP_TOP
42 LOAD_CONST 1 (None)
44 RETURN_VALUE
patched:
1 2 LOAD_NAME 0 (x)
2 4 MATCH_SEQUENCE
6 POP_JUMP_IF_FALSE 20 (to 40)
8 GET_LEN
10 LOAD_CONST 0 (4)
12 COMPARE_OP 2 (==)
14 POP_JUMP_IF_FALSE 20 (to 40)
16 UNPACK_SEQUENCE 4
18 SWAP 2
20 SWAP 3
22 SWAP 4
24 POP_JUMP_IF_NOT_NONE 18 (to 36)
26 STORE_NAME 1 (a)
28 STORE_NAME 2 (b)
30 STORE_NAME 3 (c)
3 32 LOAD_CONST 1 (None)
34 RETURN_VALUE
2 >> 36 POP_TOP
38 POP_TOP
>> 40 POP_TOP
42 LOAD_CONST 1 (None)
44 RETURN_VALUE
Replacing the ROT_FOURs with SWAPs may seem minor, but it ends up being a *lot*
less work at runtime.
----------
_______________________________________
Python tracker <[email protected]>
<https://bugs.python.org/issue46528>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
