bpo-30104: Use -fno-strict-aliasing on clang (#1376)
Python/dtoa.c is not compiled correctly with clang 4.0 and
optimization level -O2 or higher, because of an aliasing issue on the
double/ULong[2] union. Only compile dtoa.c with -fno-strict-aliasing.
LLVM bug report:
https://bugs.llvm.org//show_bug.cgi?id=31928
diff --git a/configure.ac b/configure.ac
index 2c8e246..6978b90 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1447,6 +1447,7 @@
# tweak OPT based on compiler and platform, only if the user didn't set
# it on the command line
AC_SUBST(OPT)
+AC_SUBST(CFLAGS_ALIASING)
if test "${OPT-unset}" = "unset"
then
case $GCC in
@@ -1459,30 +1460,49 @@
WRAP="-fwrapv"
fi
- # Clang also needs -fwrapv
case $CC in
- *clang*) WRAP="-fwrapv"
- ;;
+ *clang*)
+ cc_is_clang=1
+ ;;
+ *)
+ if $CC --version 2>&1 | grep -q clang
+ then
+ cc_is_clang=1
+ else
+ cc_is_clang=
+ fi
esac
+ if test -n "${cc_is_clang}"
+ then
+ # Clang also needs -fwrapv
+ WRAP="-fwrapv"
+ # bpo-30104: disable strict aliasing to compile correctly dtoa.c,
+ # see Makefile.pre.in for more information
+ CFLAGS_ALIASING="-fno-strict-aliasing"
+ fi
+
case $ac_cv_prog_cc_g in
yes)
if test "$Py_DEBUG" = 'true' ; then
# Optimization messes up debuggers, so turn it off for
# debug builds.
if "$CC" -v --help 2>/dev/null |grep -- -Og > /dev/null; then
- OPT="-g -Og -Wall $STRICT_PROTO"
+ OPT="-g -Og -Wall"
else
- OPT="-g -O0 -Wall $STRICT_PROTO"
+ OPT="-g -O0 -Wall"
fi
else
- OPT="-g $WRAP -O3 -Wall $STRICT_PROTO"
+ OPT="-g $WRAP -O3 -Wall"
fi
;;
*)
- OPT="-O3 -Wall $STRICT_PROTO"
+ OPT="-O3 -Wall"
;;
esac
+
+ OPT="$OPT $STRICT_PROTO"
+
case $ac_sys_system in
SCO_SV*) OPT="$OPT -m486 -DSCO5"
;;