New submission from Eugene Toder <elto...@gmail.com>:
If statement without else part generates unnecessary JUMP_FORWARD insn with
jumps right to the next insn:
>>> def foo(x):
if x: x = 1
>>> dis(foo)
2 0 LOAD_FAST 0 (x)
3 POP_JUMP_IF_FALSE 15
6 LOAD_CONST 1 (1)
9 STORE_FAST 0 (x)
12 JUMP_FORWARD 0 (to 15)
>> 15 LOAD_CONST 0 (None)
18 RETURN_VALUE
This patch suppresses generation of this jump.
Testing revealed another issue: when AST is produced from string empty 'orelse'
sequences are represented with NULLs. However when AST is converted from Python
AST objects empty 'orelse' is a pointer to 0-length sequence. I've changed this
to produce NULL pointers, like in the string case. This uses less memory and
doesn't introduce different code path in compiler. Without this change
test_compile failed with my first change.
make test passes.
----------
components: Interpreter Core
files: if_no_else.patch
keywords: patch
messages: 130623
nosy: eltoder
priority: normal
severity: normal
status: open
title: If without else generates redundant jump
type: performance
versions: Python 3.3
Added file: http://bugs.python.org/file21091/if_no_else.patch
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue11471>
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