diff options
author | Jeffrey Yasskin <jyasskin@gmail.com> | 2009-02-25 02:25:04 (GMT) |
---|---|---|
committer | Jeffrey Yasskin <jyasskin@gmail.com> | 2009-02-25 02:25:04 (GMT) |
commit | 9de7ec7868554e92700e4bda6c5f9d8fcad634dc (patch) | |
tree | ce9c4c821286769b6057d94ea20e337ea726f60f /Doc/library | |
parent | 0a68b01d649168f096fddd3cd8d433f2b8b6bb9e (diff) | |
download | cpython-9de7ec7868554e92700e4bda6c5f9d8fcad634dc.zip cpython-9de7ec7868554e92700e4bda6c5f9d8fcad634dc.tar.gz cpython-9de7ec7868554e92700e4bda6c5f9d8fcad634dc.tar.bz2 |
http://bugs.python.org/issue4715
This patch by Antoine Pitrou optimizes the bytecode for conditional branches by
merging the following "POP_TOP" instruction into the conditional jump. For
example, the list comprehension "[x for x in l if not x]" produced the
following bytecode:
1 0 BUILD_LIST 0
3 LOAD_FAST 0 (.0)
>> 6 FOR_ITER 23 (to 32)
9 STORE_FAST 1 (x)
12 LOAD_FAST 1 (x)
15 JUMP_IF_TRUE 10 (to 28)
18 POP_TOP
19 LOAD_FAST 1 (x)
22 LIST_APPEND 2
25 JUMP_ABSOLUTE 6
>> 28 POP_TOP
29 JUMP_ABSOLUTE 6
>> 32 RETURN_VALUE
but after the patch it produces the following bytecode:
1 0 BUILD_LIST 0
3 LOAD_FAST 0 (.0)
>> 6 FOR_ITER 18 (to 27)
9 STORE_FAST 1 (x)
12 LOAD_FAST 1 (x)
15 POP_JUMP_IF_TRUE 6
18 LOAD_FAST 1 (x)
21 LIST_APPEND 2
24 JUMP_ABSOLUTE 6
>> 27 RETURN_VALUE
Notice that not only the code is shorter, but the conditional jump
(POP_JUMP_IF_TRUE) jumps right to the start of the loop instead of going through
the JUMP_ABSOLUTE at the end. "continue" statements are helped
similarly.
Furthermore, the old jump opcodes (JUMP_IF_FALSE, JUMP_IF_TRUE) have been
replaced by two new opcodes:
- JUMP_IF_TRUE_OR_POP, which jumps if true and pops otherwise
- JUMP_IF_FALSE_OR_POP, which jumps if false and pops otherwise
Diffstat (limited to 'Doc/library')
-rw-r--r-- | Doc/library/dis.rst | 22 |
1 files changed, 16 insertions, 6 deletions
diff --git a/Doc/library/dis.rst b/Doc/library/dis.rst index 7dc8a3c..856a9e4 100644 --- a/Doc/library/dis.rst +++ b/Doc/library/dis.rst @@ -595,16 +595,26 @@ the more significant byte last. Increments bytecode counter by *delta*. -.. opcode:: JUMP_IF_TRUE (delta) +.. opcode:: POP_JUMP_IF_TRUE (target) - If TOS is true, increment the bytecode counter by *delta*. TOS is left on the - stack. + If TOS is true, sets the bytecode counter to *target*. TOS is popped. -.. opcode:: JUMP_IF_FALSE (delta) +.. opcode:: POP_JUMP_IF_FALSE (target) - If TOS is false, increment the bytecode counter by *delta*. TOS is not - changed. + If TOS is false, sets the bytecode counter to *target*. TOS is popped. + + +.. opcode:: JUMP_IF_TRUE_OR_POP (target) + + If TOS is true, sets the bytecode counter to *target* and leaves TOS + on the stack. Otherwise (TOS is false), TOS is popped. + + +.. opcode:: JUMP_IF_FALSE_OR_POP (target) + + If TOS is false, sets the bytecode counter to *target* and leaves + TOS on the stack. Otherwise (TOS is true), TOS is popped. .. opcode:: JUMP_ABSOLUTE (target) |