[m-rev.] diff: fix bug #293: asm_fast grades and GCC 4.8

[Julien Fischer]

Branches: 13.05, master

Fix bug #293: GCC 4.8 and the asm_fast grades.

configure.ac:
      Pass -fno-tree-dominator-opts to GCC 4.8 on x86-64 and x86; gcc labels
      are not working correctly in the presence of that optimisation.

NEWS:
      Announce the above.

Julien.

diff --git a/NEWS b/NEWS
index d3c6eac..18ca7e0 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,8 @@ This is a bug-fix release.
    are now applied to all executables in the Mercury system.  Likewise,
    for shared libraries and the LD_LIBFLAGS and EXTRA_LD_LIBFLAGS mmake
    variables.  (Bug #288)
+* We have added a workaround for a problem that was preventing the
+  asm_fast grades working with GCC 4.8.  (Bug #293)


  NEWS for Mercury 13.05.1
diff --git a/configure.ac b/configure.ac
index 67489a9..1a01d5e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2470,6 +2470,14 @@ case "$ac_cv_prog_gcc" in yes)
              CFLAGS_FOR_GOTOS="$CFLAGS_FOR_GOTOS -fomit-frame-pointer"
              ;;
          i*86-*|x86_64*)
+            # On x86-64 with GCC 4.8, gcc labels do not work correctly with
+            # -ftree-dominator-opts -- we disable it for x86 in this case too.
+            #
+            case "$C_COMPILER_TYPE" in
+                gcc_4_8_*)
+                  CFLAGS_FOR_GOTOS="$CFLAGS_FOR_GOTOS -fno-tree-dominator-opts"
+                ;;
+            esac
              CFLAGS_FOR_REGS="-fno-builtin -fno-omit-frame-pointer"
              ;;
          # We need a special-case hack here, because the auto-config