Use -fno-strict-aliasing if available. Fixes #766696. Will backport to 2.2.

loewis · loewis · commit 70fedcd583e1 · 2003-07-07T21:26:19.000Z
diff --git a/configure b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision: 1.421 .
+# From configure.in Revision: 1.422 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.53 for python 2.3.
 #
@@ -3645,6 +3645,49 @@ fi
 # 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... $ECHO_C" >&6
+     ac_save_cc="$CC"
+     CC="$CC -fno-strict-aliasing"
+     if test "$cross_compiling" = yes; then
+  ac_cv_no_strict_aliasing_ok=no
+else
+  cat >conftest.$ac_ext <<_ACEOF
+#line $LINENO "configure"
+#include "confdefs.h"
+int main() { return 0; }
+_ACEOF
+rm -f conftest$ac_exeext
+if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
+  (eval $ac_link) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && { ac_try='./conftest$ac_exeext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  ac_cv_no_strict_aliasing_ok=yes
+else
+  echo "$as_me: program exited with status $ac_status" >&5
+echo "$as_me: failed program was:" >&5
+cat conftest.$ac_ext >&5
+( exit $ac_status )
+ac_cv_no_strict_aliasing_ok=no
+fi
+rm -f core core.* *.core conftest$ac_exeext conftest.$ac_objext conftest.$ac_ext
+fi
+     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 $ac_cv_no_strict_aliasing_ok = yes
+    then
+      BASECFLAGS="$BASECFLAGS -fno-strict-aliasing"
+    fi
     case $ac_sys_system in
 	SCO_SV*)
 	    BASECFLAGS="$BASECFLAGS -m486 -DSCO5"
diff --git a/configure.in b/configure.in
@@ -641,6 +641,22 @@ AC_SUBST(BASECFLAGS)
 # 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 $CC accepts -fno-strict-aliasing)
+     ac_save_cc="$CC"
+     CC="$CC -fno-strict-aliasing"
+     AC_TRY_RUN([int main() { return 0; }],
+     ac_cv_no_strict_aliasing_ok=yes,
+     ac_cv_no_strict_aliasing_ok=no,
+     ac_cv_no_strict_aliasing_ok=no)
+     CC="$ac_save_cc"
+    AC_MSG_RESULT($ac_cv_no_strict_aliasing_ok)
+    if test $ac_cv_no_strict_aliasing_ok = yes
+    then
+      BASECFLAGS="$BASECFLAGS -fno-strict-aliasing"
+    fi
     case $ac_sys_system in
 	SCO_SV*)
 	    BASECFLAGS="$BASECFLAGS -m486 -DSCO5"
