except.c (push_eh_entry): Eliminate start of exception region label, as it isn't used.

	* except.c (push_eh_entry): Eliminate start of exception region
	label, as it isn't used.  Rename end_label to outer_context.
	(expand_eh_region_start_for_decl): Likewise.
	(expand_leftover_cleanups): Likewise.
	(expand_start_all_catch): Likewise.
	* except.h (eh_entry): Likewise.
	* except.c (expand_eh_region_end): Likewise.  Jump around the nop
	that we insert, so that we can optimize it away, if it is unused,
	also so that flow analysis can tell if we fall through to the end
	of a function or not so that it can know if a function that returns
	a value, in fact does or not.
Fixes g++.jason/return2.C when using -fno-sjlj-exceptions

From-SVN: r14135

gcc/except.c

@@ -533,26 +533,22 @@ copy_eh_entry (entry)
   return newentry;
 }
 
-/* Push a new eh_node entry onto STACK, and return the start label for
-   the entry.  */
+/* Push a new eh_node entry onto STACK.  */
 
-static rtx
+static void
 push_eh_entry (stack)
      struct eh_stack *stack;
 {
   struct eh_node *node = (struct eh_node *) xmalloc (sizeof (struct eh_node));
   struct eh_entry *entry = (struct eh_entry *) xmalloc (sizeof (struct eh_entry));
 
-  entry->start_label = gen_label_rtx ();
-  entry->end_label = gen_label_rtx ();
+  entry->outer_context = gen_label_rtx ();
   entry->exception_handler_label = gen_label_rtx ();
   entry->finalization = NULL_TREE;
 
   node->entry = entry;
   node->chain = stack->top;
   stack->top = node;
-
-  return entry->start_label;
 }
 
 /* Pop an entry from the given STACK.  */
@@ -1007,7 +1003,7 @@ expand_eh_region_start_for_decl (decl)
 
   if (exceptions_via_longjmp == 0)
     note = emit_note (NULL_PTR, NOTE_INSN_EH_REGION_BEG);
-  emit_label (push_eh_entry (&ehstack));
+  push_eh_entry (&ehstack);
   if (exceptions_via_longjmp == 0)
     NOTE_BLOCK_NUMBER (note)
       = CODE_LABEL_NUMBER (ehstack.top->entry->exception_handler_label);
@@ -1047,21 +1043,25 @@ expand_eh_region_end (handler)
 
   if (exceptions_via_longjmp == 0)
     {
+      rtx label;
       rtx note = emit_note (NULL_PTR, NOTE_INSN_EH_REGION_END);
       NOTE_BLOCK_NUMBER (note) = CODE_LABEL_NUMBER (entry->exception_handler_label);
-    }
 
-  /* Emit a label marking the end of this exception region.  */
-  emit_label (entry->end_label);
+      label = gen_label_rtx ();
+      emit_jump (label);
+
+      /* Emit a label marking the end of this exception region that
+	 is used for rethrowing into the outer context.  */
+      emit_label (entry->outer_context);
 
-  if (exceptions_via_longjmp == 0)
-    {
       /* Put in something that takes up space, as otherwise the end
 	 address for this EH region could have the exact same address as
 	 its outer region. This would cause us to miss the fact that
 	 resuming exception handling with this PC value would be inside
 	 the outer region.  */
       emit_insn (gen_nop ());
+      emit_barrier ();
+      emit_label (label);
     }
 
   entry->finalization = handler;
@@ -1181,11 +1181,12 @@ expand_leftover_cleanups ()
 	    emit_throw ();
 	  else
 	    {
-	      /* The below can be optimized away, and we could just fall into the
-		 next EH handler, if we are certain they are nested.  */
+	      /* The below can be optimized away, and we could just
+		 fall into the next EH handler, if we are certain they
+		 are nested.  */
 	      /* Emit code to throw to the outer context if we fall off
 		 the end of the handler.  */
-	      expand_internal_throw (entry->end_label);
+	      expand_internal_throw (entry->outer_context);
 	    }
 	}
 
@@ -1302,7 +1303,7 @@ expand_start_all_catch ()
 		 into the next EH handler) if we are certain they are
 		 nested.  */
 
-	      expand_internal_throw (entry->end_label);
+	      expand_internal_throw (entry->outer_context);
 	    }
 	}
       free (entry);

gcc/except.h

@@ -38,9 +38,7 @@ struct label_node {
 
 /* An eh_entry is used to describe one exception handling region.
 
-   START_LABEL is the label corresponding to the start of the region.
-
-   END_LABEL is the label corresponding to the end of the region.
+   OUTER_CONTEXT is the label used for rethrowing into the outer context.
 
    EXCEPTION_HANDLER_LABEL is the label corresponding to the handler
    for this region.
@@ -50,8 +48,7 @@ struct label_node {
    end of a group of try blocks.  */
 
 struct eh_entry {
-  rtx start_label;
-  rtx end_label;
+  rtx outer_context;
   rtx exception_handler_label;
 
   tree finalization;