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only use -fno-strict-aliasing when needed by compiler

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Benjamin Peterson 2010-06-21 17:04:07 +00:00
parent f7155a38cd
commit c2037d6ec8
2 changed files with 83 additions and 26 deletions
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38
configure.in
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@ -878,19 +878,37 @@ AC_SUBST(UNIVERSAL_ARCH_FLAGS)
# tweak BASECFLAGS based on compiler and platform
case $GCC in
yes)
# Python violates C99 rules, by casting between incompatible
# pointer types. GCC may generate bad code as a result of that,
# so use -fno-strict-aliasing if supported.
AC_MSG_CHECKING(whether $CC accepts -fno-strict-aliasing)
# Python doesn't violate C99 aliasing rules, but older versions of
# GCC produce warnings for legal Python code. Enable
# -fno-strict-aliasing on versions of GCC that support but produce
# warnings. See Issue3326
AC_MSG_CHECKING(whether $CC accepts and needs -fno-strict-aliasing)
ac_save_cc="$CC"
CC="$CC -fno-strict-aliasing"
AC_TRY_RUN([int main() { return 0; }],
ac_cv_no_strict_aliasing_ok=yes,
ac_cv_no_strict_aliasing_ok=no,
ac_cv_no_strict_aliasing_ok=no)
save_CFLAGS="$CFLAGS"
AC_CACHE_VAL(ac_cv_no_strict_aliasing,
AC_COMPILE_IFELSE(
[
AC_LANG_PROGRAM([[]], [[]])
],[
CC="$ac_save_cc -fstrict-aliasing"
CFLAGS="$CFLAGS -Werror -Wstrict-aliasing"
AC_COMPILE_IFELSE(
[
AC_LANG_PROGRAM([[void f(int **x) {}]],
[[double *x; f((int **) &x);]])
],[
ac_cv_no_strict_aliasing=no
],[
ac_cv_no_strict_aliasing=yes
])
],[
ac_cv_no_strict_aliasing=no
]))
CFLAGS="$save_CFLAGS"
CC="$ac_save_cc"
AC_MSG_RESULT($ac_cv_no_strict_aliasing_ok)
if test $ac_cv_no_strict_aliasing_ok = yes
AC_MSG_RESULT($ac_cv_no_strict_aliasing)
if test $ac_cv_no_strict_aliasing = yes
then
BASECFLAGS="$BASECFLAGS -fno-strict-aliasing"
fi