re PR rtl-optimization/7520 (internal compiler error in verify_local_live_at_start)

        PR optimization/7520
        * cfganal.c (flow_active_insn_p): New.
        (forwarder_block_p): Use it.

From-SVN: r57593

gcc/ChangeLog

 2002-09-27  Richard Henderson  <rth@redhat.com>
 
+	PR optimization/7520
+	* cfganal.c (flow_active_insn_p): New.
+	(forwarder_block_p): Use it.
+
+2002-09-27  Richard Henderson  <rth@redhat.com>
+
 	* emit-rtl.c (active_insn_p): Revert last change.
 
 2002-09-27  Jakub Jelinek  <jakub@redhat.com>

gcc/cfganal.c

@@ -54,7 +54,31 @@ static void flow_dfs_compute_reverse_finish
   PARAMS ((depth_first_search_ds));
 static void remove_fake_successors	PARAMS ((basic_block));
 static bool need_fake_edge_p		PARAMS ((rtx));
+static bool flow_active_insn_p		PARAMS ((rtx));
 
+/* Like active_insn_p, except keep the return value clobber around
+   even after reload.  */
+
+static bool
+flow_active_insn_p (insn)
+     rtx insn;
+{
+  if (active_insn_p (insn))
+    return true;
+
+  /* A clobber of the function return value exists for buggy 
+     programs that fail to return a value.  It's effect is to
+     keep the return value from being live across the entire
+     function.  If we allow it to be skipped, we introduce the
+     possibility for register livetime aborts.  */
+  if (GET_CODE (PATTERN (insn)) == CLOBBER
+      && GET_CODE (XEXP (PATTERN (insn), 0)) == REG
+      && REG_FUNCTION_VALUE_P (XEXP (PATTERN (insn), 0)))
+    return true;
+
+  return false;
+}
+
 /* Return true if the block has no effect and only forwards control flow to
    its single destination.  */
 
@@ -69,12 +93,12 @@ forwarder_block_p (bb)
     return false;
 
   for (insn = bb->head; insn != bb->end; insn = NEXT_INSN (insn))
-    if (INSN_P (insn) && active_insn_p (insn))
+    if (INSN_P (insn) && flow_active_insn_p (insn))
       return false;
 
   return (!INSN_P (insn)
 	  || (GET_CODE (insn) == JUMP_INSN && simplejump_p (insn))
-	  || !active_insn_p (insn));
+	  || !flow_active_insn_p (insn));
 }
 
 /* Return nonzero if we can reach target from src by falling through.  */

gcc/testsuite/gcc.c-torture/compile/20020927-1.c

+/* PR optimization/7520 */
+/* ICE at -O3 on x86 due to register life problems caused by
+   the return-without-value in bar.  */
+
+int
+foo ()
+{
+  int i;
+  long long int j;
+
+  while (1)
+    {
+      if (j & 1)
+	++i;
+      j >>= 1;
+      if (j)
+	return i;
+    }
+}
+
+int
+bar ()
+{
+  if (foo ())
+    return;
+}