[C++] Small optimizations

runtime/Cpp/runtime/src/atn/ParserATNSimulator.cpp

@@ -124,6 +124,8 @@ size_t ParserATNSimulator::adaptivePredict(TokenStream *input, size_t decision,
     } else {
       dfa::DFAState *newState = new dfa::DFAState(std::move(s0_closure)); /* mem-check: managed by the DFA or deleted below */
       s0 = addDFAState(dfa, newState);
+
+      delete dfa.s0; // Delete existing s0 DFA state, if there's any. 
       dfa.s0 = s0;
       if (s0 != newState) {
         delete newState; // If there was already a state with this config set we don't need the new one.

runtime/Cpp/runtime/src/dfa/DFA.cpp

@@ -26,35 +26,34 @@ DFA::DFA(atn::DecisionState *atnStartState, size_t decision)
     if (static_cast<atn::StarLoopEntryState *>(atnStartState)->isPrecedenceDecision) {
       _precedenceDfa = true;
       s0 = new DFAState(std::unique_ptr<atn::ATNConfigSet>(new atn::ATNConfigSet()));
-      _s0Shadow = s0;
       s0->isAcceptState = false;
       s0->requiresFullContext = false;
     }
   }
 }
 
-DFA::DFA(DFA &&other) : atnStartState(std::move(other.atnStartState)), decision(std::move(other.decision)) {
+DFA::DFA(DFA &&other) : atnStartState(other.atnStartState), decision(other.decision) {
   // Source states are implicitly cleared by the move.
   states = std::move(other.states);
 
-  // Manually move s0 pointers.
+  other.atnStartState = nullptr;
+  other.decision = 0;
   s0 = other.s0;
   other.s0 = nullptr;
-  _s0Shadow = other._s0Shadow;
-  other._s0Shadow = nullptr;
-
   _precedenceDfa = other._precedenceDfa;
+  other._precedenceDfa = false;
 }
 
 DFA::~DFA() {
-  // ml: s0 can be set either in our constructor or by external code, so we need a way to track our own creation.
-  // We could use a shared pointer again (and force that on all external assignments etc.) or just shadow it.
-  // I hesitate moving s0 to the normal states list as this might conflict with consumers of that list.
-  delete _s0Shadow;
-
+  bool s0InList = (s0 == nullptr);
   for (auto state : states) {
+    if (state == s0)
+      s0InList = true;
     delete state;
   }
+
+  if (!s0InList)
+    delete s0;
 }
 
 bool DFA::isPrecedenceDfa() const {

runtime/Cpp/runtime/src/dfa/DFA.h

@@ -20,10 +20,10 @@ namespace dfa {
     /// Set only allows you to see if it's there.
 
     /// From which ATN state did we create this DFA?
-    atn::DecisionState *const atnStartState;
+    atn::DecisionState *atnStartState;
     std::unordered_set<DFAState *, DFAState::Hasher, DFAState::Comparer> states; // States are owned by this class.
     DFAState *s0;
-    const size_t decision;
+    size_t decision;
 
     DFA(atn::DecisionState *atnStartState);
     DFA(atn::DecisionState *atnStartState, size_t decision);
@@ -85,7 +85,6 @@ namespace dfa {
      * {@code false}. This is the backing field for {@link #isPrecedenceDfa}.
      */
     bool _precedenceDfa;
-    DFAState *_s0Shadow = nullptr; // ml: assigned when we created s0 ourselves.
   };
 
 } // namespace atn

tool/resources/org/antlr/v4/tool/templates/codegen/Cpp/Cpp.stg

@@ -1024,7 +1024,7 @@ ContextRuleListIndexedGetterDecl(r) ::= <<
 
 >>
 
-LexerRuleContext() ::= "antlr4::RuleContext"
+LexerRuleContext() ::= "RuleContext"
 
 // The rule context name is the rule followed by a suffix; e.g. r becomes rContext.
 RuleContextNameSuffix() ::= "Context"