Build fails with strict-aliasing violations #246
Description
Here is some generated code in cybin.pyx -> cybin.c:
/* "cybin.pyx":102
*
* cdef inline int write_double(CyTransportBase buf, double val) except -1:
* cdef int64_t v = htobe64((<int64_t*>(&val))[0]) # <<<<<<<<<<<<<<
* buf.c_write(<char*>(&v), 8)
* return 0
*/
__pyx_v_v = htobe64((((int64_t *)(&__pyx_v_val))[0]));and
/* "cybin.pyx":290
* elif ttype == T_DOUBLE:
* n = read_i64(buf)
* return (<double*>(&n))[0] # <<<<<<<<<<<<<<
*
* elif ttype == T_BINARY:
*/
__Pyx_XDECREF(__pyx_r);
__pyx_t_2 = PyFloat_FromDouble((((double *)(&__pyx_v_n))[0])); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 290, __pyx_L1_error)
__Pyx_GOTREF(__pyx_t_2);
__pyx_r = __pyx_t_2;
__pyx_t_2 = 0;
goto __pyx_L0;Attempting to compile thriftpy2 produces the following compiler errors:
2024-03-03 15:49:54,283 root INFO x86_64-pc-linux-gnu-gcc -Wsign-compare -DNDEBUG -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-clash-protection -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wformat -Werror=format-security -Werror=implicit-function-declaration -Werror=implicit-int -Werror=int-conversion -Werror=incompatible-pointer-types -Wno-error=incompatible-pointer-types -DNDEBUG -fPIC -I/usr/include/python3.11 -c thriftpy2/protocol/cybin/cybin.c -o /var/tmp/portage/dev-python/thriftpy2-0.4.20/work/thriftpy2-0.4.20-python3_11/build/temp.linux-x86_64-cpython-311/thriftpy2/protocol/cybin/cybin.o
In file included from /usr/include/sys/types.h:176,
from /usr/include/stdlib.h:514,
from /usr/include/python3.11/Python.h:23,
from thriftpy2/protocol/cybin/cybin.c:34:
thriftpy2/protocol/cybin/cybin.c: In function ‘__pyx_f_5cybin_write_double’:
thriftpy2/protocol/cybin/cybin.c:4623:51: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
4623 | __pyx_v_v = htobe64((((int64_t *)(&__pyx_v_val))[0]));
| ^
thriftpy2/protocol/cybin/cybin.c: In function ‘__pyx_f_5cybin_c_read_val’:
thriftpy2/protocol/cybin/cybin.c:6850:61: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
6850 | __pyx_t_2 = PyFloat_FromDouble((((double *)(&__pyx_v_n))[0])); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 290, __pyx_L1_error)
| ^
I suspect there are easier ways to bitfiddle a double.