[backport gcc-4.9/trunk r199264 <mikpe@it.uu.se>]

gcc/

2013-05-23  Richard Henderson  <rth@redhat.com>

	PR target/56742
	* config/i386/i386.c (ix86_seh_fixup_eh_fallthru): New.
	(ix86_reorg): Call it.

--- gcc-4.8.0/gcc/config/i386/i386.c.~1~	2013-02-21 11:57:10.000000000 +0100
+++ gcc-4.8.0/gcc/config/i386/i386.c	2013-05-25 12:04:29.195939965 +0200
@@ -35427,6 +35427,46 @@ ix86_pad_short_function (void)
     }
 }
 
+/* Fix up a Windows system unwinder issue.  If an EH region falls thru into
+   the epilogue, the Windows system unwinder will apply epilogue logic and
+   produce incorrect offsets.  This can be avoided by adding a nop between
+   the last insn that can throw and the first insn of the epilogue.  */
+
+static void
+ix86_seh_fixup_eh_fallthru (void)
+{
+  edge e;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds)
+    {
+      rtx insn, next;
+
+      /* Find the beginning of the epilogue.  */
+      for (insn = BB_END (e->src); insn != NULL; insn = PREV_INSN (insn))
+	if (NOTE_P (insn) && NOTE_KIND (insn) == NOTE_INSN_EPILOGUE_BEG)
+	  break;
+      if (insn == NULL)
+	continue;
+
+      /* We only care about preceeding insns that can throw.  */
+      insn = prev_active_insn (insn);
+      if (insn == NULL || !can_throw_internal (insn))
+	continue;
+
+      /* Do not separate calls from their debug information.  */
+      for (next = NEXT_INSN (insn); next != NULL; next = NEXT_INSN (next))
+	if (NOTE_P (next)
+            && (NOTE_KIND (next) == NOTE_INSN_VAR_LOCATION
+                || NOTE_KIND (next) == NOTE_INSN_CALL_ARG_LOCATION))
+	  insn = next;
+	else
+	  break;
+
+      emit_insn_after (gen_nops (const1_rtx), insn);
+    }
+}
+
 /* Implement machine specific optimizations.  We implement padding of returns
    for K8 CPUs and pass to avoid 4 jumps in the single 16 byte window.  */
 static void
@@ -35436,6 +35476,9 @@ ix86_reorg (void)
      with old MDEP_REORGS that are not CFG based.  Recompute it now.  */
   compute_bb_for_insn ();
 
+  if (TARGET_SEH && current_function_has_exception_handlers ())
+    ix86_seh_fixup_eh_fallthru ();
+
   if (optimize && optimize_function_for_speed_p (cfun))
     {
       if (TARGET_PAD_SHORT_FUNCTION)