8295116: C2: assert(dead->outcnt() == 0 && !dead->is_top()) failed: node must be dead

Reviewed-by: thartmann, rcastanedalo

Author: chhagedorn

src/hotspot/share/opto/ifnode.cpp

@@ -733,6 +733,7 @@ bool IfNode::is_ctrl_folds(Node* ctrl, PhaseIterGVN* igvn) {
     ctrl->in(0)->as_If()->cmpi_folds(igvn, true) &&
     // Must compare same value
     ctrl->in(0)->in(1)->in(1)->in(1) != NULL &&
+    ctrl->in(0)->in(1)->in(1)->in(1) != igvn->C->top() &&
     ctrl->in(0)->in(1)->in(1)->in(1) == in(1)->in(1)->in(1);
 }