8330159: [C2] Remove or clarify Compile::init_start

Reviewed-by: chagedorn, dlong

src/hotspot/share/opto/compile.cpp

@@ -754,14 +754,14 @@ Compile::Compile( ciEnv* ci_env, ciMethod* target, int osr_bci,
       init_tf(TypeFunc::make(domain, range));
       StartNode* s = new StartOSRNode(root(), domain);
       initial_gvn()->set_type_bottom(s);
-      init_start(s);
+      verify_start(s);
       cg = CallGenerator::for_osr(method(), entry_bci());
     } else {
       // Normal case.
       init_tf(TypeFunc::make(method()));
       StartNode* s = new StartNode(root(), tf()->domain());
       initial_gvn()->set_type_bottom(s);
-      init_start(s);
+      verify_start(s);
       if (method()->intrinsic_id() == vmIntrinsics::_Reference_get) {
         // With java.lang.ref.reference.get() we must go through the
         // intrinsic - even when get() is the root
@@ -1105,13 +1105,12 @@ void Compile::Init(bool aliasing) {
   probe_alias_cache(nullptr)->_index = AliasIdxTop;
 }
 
-//---------------------------init_start----------------------------------------
-// Install the StartNode on this compile object.
-void Compile::init_start(StartNode* s) {
-  if (failing())
-    return; // already failing
-  assert(s == start(), "");
+#ifdef ASSERT
+// Verify that the current StartNode is valid.
+void Compile::verify_start(StartNode* s) const {
+  assert(failing() || s == start(), "should be StartNode");
 }
+#endif
 
 /**
  * Return the 'StartNode'. We must not have a pending failure, since the ideal graph

src/hotspot/share/opto/compile.hpp

@@ -864,7 +864,7 @@ class Compile : public Phase {
   RootNode*    root() const                { return _root; }
   void         set_root(RootNode* r)       { _root = r; }
   StartNode*   start() const;              // (Derived from root.)
-  void         init_start(StartNode* s);
+  void         verify_start(StartNode* s) const NOT_DEBUG_RETURN;
   Node*        immutable_memory();
 
   Node*        recent_alloc_ctl() const    { return _recent_alloc_ctl; }

src/hotspot/share/opto/generateOptoStub.cpp

@@ -261,7 +261,7 @@ void GraphKit::gen_stub(address C_function,
                                           frameptr(),
                                           returnadr());
   root()->add_req(_gvn.transform(to_exc));  // bind to root to keep live
-  C->init_start(start);
+  C->verify_start(start);
 
   //-----------------------------
   // If this is a normal subroutine return, issue the return and be done.