2011/7/29 Stefan Behnel <stefan...@behnel.de>: > [moving this here from cython-users] > > Nikolaus Rath, 13.06.2011 16:59: >> >> Stefan Behnel writes: >>> >>> Nikolaus Rath, 13.06.2011 01:18: >>>> >>>> Stefan Behnel writes: >>>>> >>>>> Nikolaus Rath, 03.06.2011 23:24: >>>>>> >>>>>> Cython 0.14 generated code triggers lots of unused-but-set-variable >>>>>> warnings (which are new in GCC 4.6). >>>>> >>>>> Hmm, that's annoying. We actually generate a lot of useless "dangling >>>>> reset to 0" statements for safety (and also as a bit of a "now unused" >>>>> hint to the C compiler). >>>>> >>>>> We could get rid of most of them based on control flow analysis, but I >>>>> actually like having them there, just in case we accidentally generate >>>>> broken code at some point. A NULL pointer is a lot safer than an >>>>> arbitrarily dangling address, especially when it comes to CPython heap >>>>> allocated memory (which doesn't necessarily get freed, so you may not >>>>> get a quick segfault but a read from dead memory). >>>> >>>> I don't quite understand. The way to get rid of the warnings is to >>>> remove the unnecessary variables. How can this result in a dangling >>>> address? You'll get a syntax error from gcc about using an undeclared >>>> variable. >>> >>> Ah, sorry. I misunderstood the meaning of the warning message as >>> pointing at unnecessary assignments in general. Could you post a C >>> code snippet (and the corresponding Cython code) that triggers this? I >>> don't have gcc 4.6 available for testing. >> >> Sure. It's apparently triggered by unused function arguments: >> >> $ cat test.pyx >> class Operations(object): >> def handle_exc(self, fn, exc): >> pass >> >> $ cython test.pyx >> >> $ gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall >> -Wstrict-prototypes -fPIC -I/usr/include/python2.6 -c test.c -o test.o >> -D_FILE_OFFSET_BITS=64 -I/usr/include/fuse -Werror -Wall -Wextra >> -Wconversion -Wno-unused-parameter -Wno-sign-conversion -fno-strict-aliasing >> test.c: >> test.c:454:13: warning: variable ‘__pyx_v_exc’ set but not used >> [-Wunused-but-set-variable] >> test.c:453:13: warning: variable ‘__pyx_v_fn’ set but not used >> [-Wunused-but-set-variable] >> test.c:452:13: warning: variable ‘__pyx_v_self’ set but not used >> [-Wunused-but-set-variable] > > http://trac.cython.org/cython_trac/ticket/704 > > I think this is something that the control flow analysis could deal with. > Basically, every parameter that turns out to be unused in the function (and > this most likely only happens with parameters) could be ignored, unless it > requires a type conversion with potential side effects. In that (unlikely) > case, we could still drop the final assignment to the variable itself. >
There is entry.cf_unused flag it's set when the whole entry is not used. -- vitja. _______________________________________________ cython-devel mailing list cython-devel@python.org http://mail.python.org/mailman/listinfo/cython-devel
