[evaluator] Avoid recording dependency sources and sinks when disabled

Short-circuit the logic here early to avoid the dependency logic if
recording is disabled.

Author: hamishknight

include/swift/AST/Evaluator.h

@@ -414,6 +414,8 @@ class Evaluator {
             typename std::enable_if<Request::isDependencySink>::type * = nullptr>
   void handleDependencySinkRequest(const Request &r,
                                    const typename Request::OutputType &o) {
+    if (!recorder.isRecordingEnabled())
+      return;
     evaluator::DependencyCollector collector(recorder);
     r.writeDependencySink(collector, o);
   }
@@ -425,6 +427,8 @@ class Evaluator {
   template <typename Request,
             typename std::enable_if<Request::isDependencySource>::type * = nullptr>
   void handleDependencySourceRequest(const Request &r) {
+    if (!recorder.isRecordingEnabled())
+      return;
     auto source = r.readDependencySource(recorder);
     if (!source.isNull() && source.get()->isPrimary()) {
       recorder.handleDependencySourceRequest(r, source.get());

include/swift/AST/EvaluatorDependencies.h

@@ -94,6 +94,9 @@ class DependencyRecorder {
 public:
   DependencyRecorder(bool shouldRecord) : shouldRecord(shouldRecord) {}
 
+  /// Whether dependency recording is enabled.
+  bool isRecordingEnabled() const { return shouldRecord; }
+
   /// Push a new empty set onto the activeRequestReferences stack.
   template<typename Request>
   void beginRequest();