New issue 2883: Bytecode contains jump-to-unconditional-jump
https://bitbucket.org/pypy/pypy/issues/2883/bytecode-contains-jump-to-unconditional
Vincent Pelletier:
Found while comparing cPython 2.7.15 with pypy 6.0.0.
This seems suboptimal, any jump (conditional or not) jumping to an interrupted
chain of unconditional jumps should be possible to simplify by updating
original instruction to jump to the last element in that chain, modulo
absolute/relative addressing considerations. In below example, 19 jump to 29
which is an unconditional jump.
I tried poking at pypy/astcompiler/assemble.py:_resolve_block_targets but could
not get good enough results. I am not sure all the code is visible to it
(code-less blocks ?).
Also, "<n> JUMP <n+1>" (below, 29 jumps to 32) instructions should be possible
to remove entirely (which may require updating anything jumping to that
instruction).
$ python -c "import dis, t; dis.dis(t)" > cpython.t.pydis
$ pypy -c "import dis, t; dis.dis(t)" > pypy.t.pydis
$ diff -u cpython.t.pydis pypy.t.pydis
--- cpython.t.pydis 2018-09-09 06:03:51.763765156 +0000
+++ pypy.t.pydis 2018-09-09 06:04:02.987767118 +0000
@@ -16,12 +16,12 @@
10 12 LOAD_GLOBAL 0 (bar)
15 CALL_FUNCTION 0
18 POP_TOP
- 19 JUMP_ABSOLUTE 32
+ 19 JUMP_FORWARD 7 (to 29)
12 >> 22 LOAD_GLOBAL 1 (baz)
25 CALL_FUNCTION 0
28 POP_TOP
- 29 JUMP_FORWARD 0 (to 32)
+ >> 29 JUMP_FORWARD 0 (to 32)
>> 32 LOAD_CONST 0 (None)
35 RETURN_VALUE
$ cat t.py
def bar():
pass
def baz():
pass
def foo(a, b):
if a:
if b:
bar()
else:
baz()
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