Expand and update comments.

Author: bazuzi

clang/include/clang/Analysis/FlowSensitive/ASTOps.h

@@ -146,9 +146,9 @@ struct ReferencedDecls {
   /// Free functions and member functions which are referenced (but not
   /// necessarily called).
   llvm::DenseSet<const FunctionDecl *> Functions;
-  /// Parameters of other functions, captured by reference by a lambda. This is
-  /// empty except when ReferencedDecls are computed for a lambda's call
-  /// operator.
+  /// When analyzing a lambda's call operator, the set of all parameters (from
+  /// the surrounding function) that the lambda captures. Captured local
+  /// variables are already included in `Locals` above.
   llvm::DenseSet<const ParmVarDecl *> LambdaCapturedParams;
 };
 

clang/lib/Analysis/FlowSensitive/ASTOps.cpp

@@ -282,6 +282,17 @@ ReferencedDecls getReferencedDecls(const FunctionDecl &FD) {
   Visitor.TraverseStmt(FD.getBody());
   if (const auto *CtorDecl = dyn_cast<CXXConstructorDecl>(&FD))
     Visitor.traverseConstructorInits(CtorDecl);
+
+  // If analyzing a lambda call operator, collect all captures of parameters (of
+  // the surrounding function). This collects them even if they are not
+  // referenced in the body of the lambda call operator. Non-parameter local
+  // variables that are captured are already collected into
+  // `ReferencedDecls.Locals` when traversing the call operator body, but we
+  // collect parameters here to avoid needing to check at each referencing node
+  // whether the parameter is a lambda capture from a surrounding function or is
+  // a parameter of the current function. If it becomes necessary to limit this
+  // set to the parameters actually referenced in the body, alternative
+  // optimizations can be implemented to minimize duplicative work.
   if (const auto *Method = dyn_cast<CXXMethodDecl>(&FD);
       Method && isLambdaCallOperator(Method)) {
     for (const auto &Capture : Method->getParent()->captures()) {