Author: benjamin.peterson Date: Tue Mar 30 19:34:47 2010 New Revision: 79499 Log: build without -fno-strict-aliasing when gcc isn't buggy #3326 Patch from Daniel Stutzbach Modified: python/branches/py3k/Misc/NEWS python/branches/py3k/configure python/branches/py3k/configure.in Modified: python/branches/py3k/Misc/NEWS ============================================================================== --- python/branches/py3k/Misc/NEWS (original) +++ python/branches/py3k/Misc/NEWS Tue Mar 30 19:34:47 2010 @@ -883,6 +883,9 @@ Build ----- +- Issue #3326: Build Python without -fno-strict-aliasing when the gcc does not + give false warnings. + - Issue #1628484: The Makefile doesn't ignore the CFLAGS environment variable anymore. It also forwards the LDFLAGS settings to the linker when building a shared library. Modified: python/branches/py3k/configure ============================================================================== --- python/branches/py3k/configure (original) +++ python/branches/py3k/configure Tue Mar 30 19:34:47 2010 @@ -1,5 +1,5 @@ #! /bin/sh -# From configure.in Revision: 78965 . +# From configure.in Revision: 79401 . # Guess values for system-dependent variables and create Makefiles. # Generated by GNU Autoconf 2.61 for python 3.2. # @@ -4569,14 +4569,16 @@ # tweak BASECFLAGS based on compiler and platform case $GCC in yes) - # Python violates C99 rules, by casting between incompatible - # pointer types. GCC may generate bad code as a result of that, - # so use -fno-strict-aliasing if supported. - { echo "$as_me:$LINENO: checking whether $CC accepts -fno-strict-aliasing" >&5 -echo $ECHO_N "checking whether $CC accepts -fno-strict-aliasing... $ECHO_C" >&6; } + # Python doesn't violate C99 aliasing rules, but older versions of + # GCC produce warnings for legal Python code. Enable + # -fno-strict-aliasing on versions of GCC that support but produce + # warnings. See Issue3326 + { echo "$as_me:$LINENO: checking whether $CC accepts and needs -fno-strict-aliasing" >&5 +echo $ECHO_N "checking whether $CC accepts and needs -fno-strict-aliasing... $ECHO_C" >&6; } ac_save_cc="$CC" CC="$CC -fno-strict-aliasing" - if test "${ac_cv_no_strict_aliasing_ok+set}" = set; then + save_CFLAGS="$CFLAGS" + if test "${ac_cv_no_strict_aliasing+set}" = set; then echo $ECHO_N "(cached) $ECHO_C" >&6 else cat >conftest.$ac_ext <<_ACEOF @@ -4611,21 +4613,64 @@ test -z "$ac_c_werror_flag" || test ! -s conftest.err } && test -s conftest.$ac_objext; then - ac_cv_no_strict_aliasing_ok=yes + CC="$ac_save_cc -fstrict-aliasing" + CFLAGS="$CFLAGS -Werror -Wstrict-aliasing" + cat >conftest.$ac_ext <<_ACEOF +/* confdefs.h. */ +_ACEOF +cat confdefs.h >>conftest.$ac_ext +cat >>conftest.$ac_ext <<_ACEOF +/* end confdefs.h. */ + +int +main () +{ +void f(int **x) {} int main() { double *x; f((int **) &x); return 0; } + ; + return 0; +} +_ACEOF +rm -f conftest.$ac_objext +if { (ac_try="$ac_compile" +case "(($ac_try" in + *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;; + *) ac_try_echo=$ac_try;; +esac +eval "echo \"\$as_me:$LINENO: $ac_try_echo\"") >&5 + (eval "$ac_compile") 2>conftest.er1 + ac_status=$? + grep -v '^ *+' conftest.er1 >conftest.err + rm -f conftest.er1 + cat conftest.err >&5 + echo "$as_me:$LINENO: \$? = $ac_status" >&5 + (exit $ac_status); } && { + test -z "$ac_c_werror_flag" || + test ! -s conftest.err + } && test -s conftest.$ac_objext; then + ac_cv_no_strict_aliasing=no +else + echo "$as_me: failed program was:" >&5 +sed 's/^/| /' conftest.$ac_ext >&5 + + ac_cv_no_strict_aliasing=yes +fi + +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext else echo "$as_me: failed program was:" >&5 sed 's/^/| /' conftest.$ac_ext >&5 - ac_cv_no_strict_aliasing_ok=no + ac_cv_no_strict_aliasing=no fi rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext fi + CFLAGS="$save_CFLAGS" CC="$ac_save_cc" - { echo "$as_me:$LINENO: result: $ac_cv_no_strict_aliasing_ok" >&5 -echo "${ECHO_T}$ac_cv_no_strict_aliasing_ok" >&6; } - if test $ac_cv_no_strict_aliasing_ok = yes + { echo "$as_me:$LINENO: result: $ac_cv_no_strict_aliasing" >&5 +echo "${ECHO_T}$ac_cv_no_strict_aliasing" >&6; } + if test $ac_cv_no_strict_aliasing = yes then BASECFLAGS="$BASECFLAGS -fno-strict-aliasing" fi Modified: python/branches/py3k/configure.in ============================================================================== --- python/branches/py3k/configure.in (original) +++ python/branches/py3k/configure.in Tue Mar 30 19:34:47 2010 @@ -867,19 +867,26 @@ # 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="$CC -fno-strict-aliasing" - AC_CACHE_VAL(ac_cv_no_strict_aliasing_ok, - AC_TRY_COMPILE([],[int main() { return 0; }], - ac_cv_no_strict_aliasing_ok=yes, - ac_cv_no_strict_aliasing_ok=no)) + save_CFLAGS="$CFLAGS" + AC_CACHE_VAL(ac_cv_no_strict_aliasing, + AC_TRY_COMPILE([],[int main() { return 0; }], + CC="$ac_save_cc -fstrict-aliasing" + CFLAGS="$CFLAGS -Werror -Wstrict-aliasing" + AC_TRY_COMPILE([],[void f(int **x) {} int main() { double *x; f((int **) &x); return 0; }], + 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