[pypy-dev] hunting for reason of a failing test (rpython/memory/test/)

[Gregor Wegberg]

Hi,

I'm working on an object pinning feature for incminimark right now. 
There is always one failing test (depending on the platform) 
in rpython/memory/test/test_incminimark_gc.py which I just can't solve. 
I'd appreciate any form of help. Even if it is just a "I may imagine 
that it is connected to X and Y" :-)

Basic resources:
- all my changes are in the following fork & branch: 
https://bitbucket.org/groggi/pypy/branch/gc-incminimark-pinning
- my `gc-incminimark-pinning` branch is based on PyPy's `release-2.3.x` 
branch
- pinning should work for "simple" objects, i.e. basically RPython 
strings. GC cards are not supported. More tests are needed of course.
- I am "gregor_w" in #pypy, so feel free to ping me

The following test results I get on the three major platforms running 
pytest on /rpython/memory/test:
- Windows (Visual Studio 2013 native tools): 
http://paste.pound-python.org/show/LPw4eCHE1EsfFTykQkWA/
   => failing test: test_print_leak

- OS X (clang): http://paste.pound-python.org/show/l85sUl56UCMDVxu1vrSS/
   => failing test: test_tagged_id

- Ubuntu (gcc): http://paste.pound-python.org/show/oAYctWSzF3OpqLtlBlUX/
   => failing tests: test_tagged_id

I have no idea why on Windows I get an other test to fail and 
test_tagged_id passes. However, maybe this gives you a hint.

I imagine that one of the following three reasons are responsible for 
the failing tests:
1.) I did some address calculations wrong inside incminimark. However, 
I'd expect to see way more failing tests in this case.
2.) My changes to get the GC transformation working with pin()/unpin() 
or the translation for the same two functions is wrong, so there is some 
error in
   rpython/memory/gctransform/framework.py,
   rpython/memory/gctransform/transform.py,
   rpython/rtyper/llinterp.py or
   rpython/rtyper/lltypesystem/lloperation.py.
   On the other hand I can translate PyPy with a PyPy binary containing 
my changes -- so this seems also somehow impossible?!
3.) It is some side effect as a result of the following changeset 
(llarena and lltype modification): 
https://bitbucket.org/groggi/pypy/commits/84898085a09814d1ec4f6b2b0d4202c7a985c0f9

I tried my best to check all three explanations and some more. However, 
I just can't see what is going wrong.

What I observed (only on OS X right now):
- changing `taggedpointers` to False solves the problem, i.e. test passes
- splitting both `print` statements inside the `fn` function into six 
prints with only one parameter (`print a, b, c` -> `print a\n print b\n 
print c`) leads to an error while executing the `print x`
- splitting the `print` statements again as before *and* setting 
`taggedpointers` to False leads to the same error as the original 
version of the test without modifications.

After 13-15 work hours trying to solve the bug I'm just lost. I have the 
feeling that it is something stupid and/or simple but my lack of PyPy 
knowledge stops me from seeing it. Any help is very much appreciated.

Cheers and thank you in advance,
Gregor