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

This commit is contained in:
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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71
configure vendored
View File

@ -5295,33 +5295,72 @@ 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.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC accepts -fno-strict-aliasing" >&5
$as_echo_n "checking whether $CC accepts -fno-strict-aliasing... " >&6; }
# 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
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC accepts and needs -fno-strict-aliasing" >&5
$as_echo_n "checking whether $CC accepts and needs -fno-strict-aliasing... " >&6; }
ac_save_cc="$CC"
CC="$CC -fno-strict-aliasing"
if test "$cross_compiling" = yes; then :
ac_cv_no_strict_aliasing_ok=no
save_CFLAGS="$CFLAGS"
if test "${ac_cv_no_strict_aliasing+set}" = set; then :
$as_echo_n "(cached) " >&6
else
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
int main() { return 0; }
int
main ()
{
;
return 0;
}
_ACEOF
if ac_fn_c_try_run "$LINENO"; then :
ac_cv_no_strict_aliasing_ok=yes
if ac_fn_c_try_compile "$LINENO"; then :
CC="$ac_save_cc -fstrict-aliasing"
CFLAGS="$CFLAGS -Werror -Wstrict-aliasing"
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
void f(int **x) {}
int
main ()
{
double *x; f((int **) &x);
;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"; then :
ac_cv_no_strict_aliasing=no
else
ac_cv_no_strict_aliasing_ok=no
ac_cv_no_strict_aliasing=yes
fi
rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
conftest.$ac_objext conftest.beam conftest.$ac_ext
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
else
ac_cv_no_strict_aliasing=no
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
fi
CFLAGS="$save_CFLAGS"
CC="$ac_save_cc"
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_no_strict_aliasing_ok" >&5
$as_echo "$ac_cv_no_strict_aliasing_ok" >&6; }
if test $ac_cv_no_strict_aliasing_ok = yes
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_no_strict_aliasing" >&5
$as_echo "$ac_cv_no_strict_aliasing" >&6; }
if test $ac_cv_no_strict_aliasing = yes
then
BASECFLAGS="$BASECFLAGS -fno-strict-aliasing"
fi

38
configure.in
View File

@ -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