Index: lib/Tooling/ASTDiff/ASTDiff.cpp
===================================================================
--- lib/Tooling/ASTDiff/ASTDiff.cpp
+++ lib/Tooling/ASTDiff/ASTDiff.cpp
@@ -162,9 +162,20 @@
   if (!N)
     return true;
   SourceLocation SLoc = N->getLocStart();
-  return SLoc.isValid() && SrcMgr.isInSystemHeader(SLoc);
+  if (!SLoc.isValid())
+    return false;
+  // Ignore everything from other files.
+  if (!SrcMgr.isInMainFile(SLoc))
+    return true;
+  // Ignore macros.
+  if (N->getLocStart() != SrcMgr.getSpellingLoc(N->getLocStart()))
+    return true;
+  return false;
 }
 
+static bool isDeclExcluded(const Decl *D) { return D->isImplicit(); }
+static bool isStmtExcluded(const Stmt *S) { return false; }
+
 namespace {
 /// Counts the number of nodes that will be compared.
 struct NodeCountVisitor : public RecursiveASTVisitor<NodeCountVisitor> {
@@ -172,14 +183,16 @@
   const SyntaxTree::Impl &Tree;
   NodeCountVisitor(const SyntaxTree::Impl &Tree) : Tree(Tree) {}
   bool TraverseDecl(Decl *D) {
-    if (isNodeExcluded(Tree.AST.getSourceManager(), D))
+    if (isNodeExcluded(Tree.AST.getSourceManager(), D) || isDeclExcluded(D))
       return true;
     ++Count;
     RecursiveASTVisitor<NodeCountVisitor>::TraverseDecl(D);
     return true;
   }
   bool TraverseStmt(Stmt *S) {
-    if (isNodeExcluded(Tree.AST.getSourceManager(), S))
+    if (S)
+      S = S->IgnoreImplicit();
+    if (isNodeExcluded(Tree.AST.getSourceManager(), S) || isStmtExcluded(S))
       return true;
     ++Count;
     RecursiveASTVisitor<NodeCountVisitor>::TraverseStmt(S);
@@ -233,7 +246,7 @@
       N.Height = std::max(N.Height, 1 + Tree.getNode(Child).Height);
   }
   bool TraverseDecl(Decl *D) {
-    if (isNodeExcluded(Tree.AST.getSourceManager(), D))
+    if (isNodeExcluded(Tree.AST.getSourceManager(), D) || isDeclExcluded(D))
       return true;
     auto SavedState = PreTraverse(D);
     RecursiveASTVisitor<PreorderVisitor>::TraverseDecl(D);
@@ -241,7 +254,9 @@
     return true;
   }
   bool TraverseStmt(Stmt *S) {
-    if (isNodeExcluded(Tree.AST.getSourceManager(), S))
+    if (S)
+      S = S->IgnoreImplicit();
+    if (isNodeExcluded(Tree.AST.getSourceManager(), S) || isStmtExcluded(S))
       return true;
     auto SavedState = PreTraverse(S);
     RecursiveASTVisitor<PreorderVisitor>::TraverseStmt(S);
Index: test/Tooling/clang-diff-ast.cpp
===================================================================
--- test/Tooling/clang-diff-ast.cpp
+++ test/Tooling/clang-diff-ast.cpp
@@ -12,7 +12,8 @@
   // CHECK: IntegerLiteral: 1
   auto i = 1;
   // CHECK: CallExpr(
-  // CHECK: DeclRefExpr: f(
+  // CHECK-NOT: ImplicitCastExpr
+  // CHECK-NEXT: DeclRefExpr: f(
   f();
   // CHECK: BinaryOperator: =(
   i = i;
@@ -37,6 +38,7 @@
     if (i == 0)
       // CHECK: StringLiteral: foo(
       return "foo";
+    // CHECK-NOT: ImplicitCastExpr
     return 0;
   }
 
@@ -48,3 +50,22 @@
     int x = m;
   }
 };
+
+#define M (void)1
+#define MA(a, b) (void)a, b
+// CHECK: FunctionDecl
+// CHECK-NEXT: CompoundStmt
+void macros() {
+  M;
+  MA(1, 2);
+}
+// CHECK-NEXT: NamespaceDecl
+
+#ifndef GUARD
+#define GUARD
+namespace world {
+// nodes from other files are excluded
+// CHECK-NOT {{.}}
+#include "clang-diff-ast.cpp"
+}
+#endif