Disable -faggressive-loop-optimizations in gcc 4.8+ for pre-9.2 branches.

With this optimization flag enabled, recent versions of gcc can generate
incorrect code that assumes variable-length arrays (such as oidvector)
are actually fixed-length because they're embedded in some larger struct.
The known instance of this problem was fixed in 9.2 and up by commit
8137f2c323 and followon work, which hides
actually-variable-length catalog fields from the compiler altogether.
And we plan to gradually convert variable-length fields to official
"flexible array member" notation over time, which should prevent this type
of bug from reappearing as gcc gets smarter.  We're not going to try to
back-port those changes into older branches, though, so apply this
band-aid instead.

Andres Freund

configure

@@ -4367,6 +4367,68 @@ if test x"$pgac_cv_prog_cc_cflags__fexcess_precision_standard" = x"yes"; then
   CFLAGS="$CFLAGS -fexcess-precision=standard"
 fi
 
+  # Disable loop optimizations that get confused by variable-length struct
+  # declarations in gcc 4.8+
+  { $as_echo "$as_me:$LINENO: checking whether $CC supports -fno-aggressive-loop-optimizations" >&5
+$as_echo_n "checking whether $CC supports -fno-aggressive-loop-optimizations... " >&6; }
+if test "${pgac_cv_prog_cc_cflags__fno_aggressive_loop_optimizations+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -fno-aggressive-loop-optimizations"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+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=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$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
+  pgac_cv_prog_cc_cflags__fno_aggressive_loop_optimizations=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	pgac_cv_prog_cc_cflags__fno_aggressive_loop_optimizations=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+fi
+{ $as_echo "$as_me:$LINENO: result: $pgac_cv_prog_cc_cflags__fno_aggressive_loop_optimizations" >&5
+$as_echo "$pgac_cv_prog_cc_cflags__fno_aggressive_loop_optimizations" >&6; }
+if test x"$pgac_cv_prog_cc_cflags__fno_aggressive_loop_optimizations" = x"yes"; then
+  CFLAGS="$CFLAGS -fno-aggressive-loop-optimizations"
+fi
+
 elif test "$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.

configure.in

@@ -438,6 +438,9 @@ if test "$GCC" = yes -a "$ICC" = no; then
   PGAC_PROG_CC_CFLAGS_OPT([-fwrapv])
   # Disable FP optimizations that cause various errors on gcc 4.5+ or maybe 4.6+
   PGAC_PROG_CC_CFLAGS_OPT([-fexcess-precision=standard])
+  # Disable loop optimizations that get confused by variable-length struct
+  # declarations in gcc 4.8+
+  PGAC_PROG_CC_CFLAGS_OPT([-fno-aggressive-loop-optimizations])
 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.