Index: clang-tidy/misc/UnusedParametersCheck.cpp
===================================================================
--- clang-tidy/misc/UnusedParametersCheck.cpp
+++ clang-tidy/misc/UnusedParametersCheck.cpp
@@ -74,7 +74,7 @@
 class UnusedParametersCheck::IndexerVisitor
     : public RecursiveASTVisitor<IndexerVisitor> {
 public:
-  IndexerVisitor(TranslationUnitDecl *Top) { TraverseDecl(Top); }
+  IndexerVisitor(ASTContext &Ctx) { TraverseAST(Ctx); }
 
   const std::unordered_set<const CallExpr *> &
   getFnCalls(const FunctionDecl *Fn) {
@@ -136,8 +136,7 @@
   auto MyDiag = diag(Param->getLocation(), "parameter %0 is unused") << Param;
 
   if (!Indexer) {
-    Indexer = llvm::make_unique<IndexerVisitor>(
-        Result.Context->getTranslationUnitDecl());
+    Indexer = llvm::make_unique<IndexerVisitor>(*Result.Context);
   }
 
   // Comment out parameter name for non-local functions.
Index: clang-tidy/modernize/LoopConvertCheck.cpp
===================================================================
--- clang-tidy/modernize/LoopConvertCheck.cpp
+++ clang-tidy/modernize/LoopConvertCheck.cpp
@@ -899,7 +899,7 @@
   // variable declared inside the loop outside of it.
   // FIXME: Determine when the external dependency isn't an expression converted
   // by another loop.
-  TUInfo->getParentFinder().gatherAncestors(Context->getTranslationUnitDecl());
+  TUInfo->getParentFinder().gatherAncestors(*Context);
   DependencyFinderASTVisitor DependencyFinder(
       &TUInfo->getParentFinder().getStmtToParentStmtMap(),
       &TUInfo->getParentFinder().getDeclToParentStmtMap(),
Index: clang-tidy/modernize/LoopConvertUtils.h
===================================================================
--- clang-tidy/modernize/LoopConvertUtils.h
+++ clang-tidy/modernize/LoopConvertUtils.h
@@ -56,12 +56,12 @@
 public:
   StmtAncestorASTVisitor() { StmtStack.push_back(nullptr); }
 
-  /// \brief Run the analysis on the TranslationUnitDecl.
+  /// \brief Run the analysis on the AST.
   ///
   /// In case we're running this analysis multiple times, don't repeat the work.
-  void gatherAncestors(const clang::TranslationUnitDecl *T) {
+  void gatherAncestors(ASTContext &Ctx) {
     if (StmtAncestors.empty())
-      TraverseDecl(const_cast<clang::TranslationUnitDecl *>(T));
+      TraverseAST(Ctx);
   }
 
   /// Accessor for StmtAncestors.
Index: clang-tidy/readability/SimplifyBooleanExprCheck.h
===================================================================
--- clang-tidy/readability/SimplifyBooleanExprCheck.h
+++ clang-tidy/readability/SimplifyBooleanExprCheck.h
@@ -79,6 +79,7 @@
                  SourceLocation Loc, StringRef Description,
                  SourceRange ReplacementRange, StringRef Replacement);
 
+  bool MatchedOnce = false;
   const bool ChainedConditionalReturn;
   const bool ChainedConditionalAssignment;
 };
Index: clang-tidy/readability/SimplifyBooleanExprCheck.cpp
===================================================================
--- clang-tidy/readability/SimplifyBooleanExprCheck.cpp
+++ clang-tidy/readability/SimplifyBooleanExprCheck.cpp
@@ -507,8 +507,16 @@
                 ChainedConditionalAssignment);
 }
 
+// This is a silly hack to let us run a RecursiveASTVisitor on the Context.
+// We want to match exactly one node in the AST, doesn't matter which.
+AST_MATCHER_P(Decl, matchOnce, bool *, Matched) {
+  if (*Matched)
+    return false;
+  return *Matched = true;
+}
+
 void SimplifyBooleanExprCheck::registerMatchers(MatchFinder *Finder) {
-  Finder->addMatcher(translationUnitDecl().bind("top"), this);
+  Finder->addMatcher(matchOnce(&MatchedOnce), this);
 
   matchBoolCondition(Finder, true, ConditionThenStmtId);
   matchBoolCondition(Finder, false, ConditionElseStmtId);
@@ -556,8 +564,8 @@
   else if (const auto *Compound =
                Result.Nodes.getNodeAs<CompoundStmt>(CompoundNotBoolId))
     replaceCompoundReturnWithCondition(Result, Compound, true);
-  else if (const auto TU = Result.Nodes.getNodeAs<Decl>("top"))
-    Visitor(this, Result).TraverseDecl(const_cast<Decl*>(TU));
+  else // MatchOnce matcher
+    Visitor(this, Result).TraverseAST(*Result.Context);
 }
 
 void SimplifyBooleanExprCheck::issueDiag(