Use -fwrapv in CFLAGS if we are using a version of gcc that accepts this flag.

This prevents compiler optimizations that assume overflow won't occur, which
breaks numerous overflow tests that we need to have working.  It is known
that gcc 4.3 causes problems and possible that 4.1 does.  Per my proposal
of some time ago and a recent report from Kris Jurka.

Backpatch as far as 8.0, which is as far as the patch conveniently goes.
7.x was pretty short of overflow tests anyway, so it may not matter there,
even assuming that anyone cares whether 7.x builds on recent gcc.

diff --git a/configure b/configure
index 476ce76c8ad5672ad56ad5d1237a7e3ea3d662dc..c93694a0a2c931762c8c55eeafee0bf88c8ba0f7 100755 (executable)
--- a/configure
+++ b/configure
@@ -3563,6 +3563,56 @@ sed 's/^/| /' conftest.$ac_ext >&5
 echo "${ECHO_T}no" >&6; }
 fi
 
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+  # Disable optimizations that assume no overflow; needed for gcc 4.3+
+  { echo "$as_me:$LINENO: checking if $CC supports -fwrapv" >&5
+echo $ECHO_N "checking if $CC supports -fwrapv... $ECHO_C" >&6; }
+pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -fwrapv"
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  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.$ac_objext; then
+  { echo "$as_me:$LINENO: result: yes" >&5
+echo "${ECHO_T}yes" >&6; }
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+       CFLAGS="$pgac_save_CFLAGS"
+                    { echo "$as_me:$LINENO: result: no" >&5
+echo "${ECHO_T}no" >&6; }
+fi
+
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 
 elif test "$ICC" = yes; then

diff --git a/configure.in b/configure.in
index d3e5765748a49dc8392bdf99e8881ce93257d594..e1582aa91f8bd0355ae14ada705099e5bfe8907f 100644 (file)
--- a/configure.in
+++ b/configure.in
@@ -284,6 +284,8 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CC_CFLAGS_OPT([-Wendif-labels])
   # Disable strict-aliasing rules; needed for gcc 3.3+
   PGAC_PROG_CC_CFLAGS_OPT([-fno-strict-aliasing])
+  # Disable optimizations that assume no overflow; needed for gcc 4.3+
+  PGAC_PROG_CC_CFLAGS_OPT([-fwrapv])
 elif test "$ICC" = yes; then
   # Intel's compiler has a bug/misoptimization in checking for
   # division by NAN (NaN == 0), -mp1 fixes it, so add it to the CFLAGS.