New submission from Antoine Pitrou <pit...@free.fr>:
This patch optimizes the bytecode for conditional branches.
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) could
profitably be replaced by two new opcodes:
- one which jumps if true and pops otherwise
- one which jumps if false and pops otherwise
----------
components: Interpreter Core
files: condbranches.patch
keywords: patch
messages: 78159
nosy: pitrou
severity: normal
stage: patch review
status: open
title: optimize bytecode for conditional branches
type: resource usage
versions: Python 3.1
Added file: http://bugs.python.org/file12419/condbranches.patch
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue4715>
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