On Tue, Jul 2, 2013 at 4:54 AM, Yury V. Zaytsev <y...@shurup.com> wrote: > Hi, > > The simplest possible program using memory views compiles with a large > number of warnings for me, even for a rather outdated version of gcc: > > def hello(int [:] a): > print(a, "world") > > If I translate it with the latest released version of Cython like this: > > cython cpp.pyx > cython --cplus cpp.pyx > > and compile like this: > > gcc -O3 -march=native -Wall -fPIC > -I/opt/ActivePython-2.7/include/python2.7 -c ./cpp.c -o cpp.o > g++ -O3 -march=native -Wall -fPIC > -I/opt/ActivePython-2.7/include/python2.7 -c ./cpp.cpp -o cpp.o > > I get lots of warnings (see attached). > > It doesn't seem to be related to C++ as such, but rather it seems that > the memory views code indeed somehow violates strict-aliasing rules. > > I'm not sure of how severe it is, but the documentation seems to suggest > that this might even lead to incorrect results. > > Can this possibly be fixed in Cython and how important is that? Shall I > create a bug report on the Trac? Is my only resort to test whether the > compiler supports -fno-strict-aliasing and use that?
You should compile with -fno-strict-aliasing--if you were using distutils rather than gcc directly it should add the all necessary flags for you. Aliasing different pointer types is necessary for Cython--it's how it implements inheritance (in plain C, a PyObject* could be a pointer to a list or dict or your own cdef class--pointer aliasing right there. Also with memory views (and numpy arrays), the underlying data is allocated as a char* and interpreted as a float* or int* or according to the metadata in the array. - Robert _______________________________________________ cython-devel mailing list cython-devel@python.org http://mail.python.org/mailman/listinfo/cython-devel
