[Constraint solver] Sink Expr::getPreorderIndexMap() into its client.

Author: DougGregor

include/swift/AST/Expr.h

@@ -530,12 +530,6 @@ class alignas(8) Expr {
   /// the parent map.
   llvm::DenseMap<Expr *, Expr *> getParentMap();
 
-  /// Produce a mapping from each expression to its index according to a
-  /// preorder traversal of the expressions. The parent has index 0, its first
-  /// child has index 1, its second child has index 2 if the first child is a
-  /// leaf node, etc.
-  llvm::DenseMap<Expr *, unsigned> getPreorderIndexMap();
-
   SWIFT_DEBUG_DUMP;
   void dump(raw_ostream &OS, unsigned Indent = 0) const;
   void dump(raw_ostream &OS, llvm::function_ref<Type(const Expr *)> getType,

lib/AST/Expr.cpp

@@ -721,28 +721,6 @@ llvm::DenseMap<Expr *, Expr *> Expr::getParentMap() {
   return parentMap;
 }
 
-llvm::DenseMap<Expr *, unsigned> Expr::getPreorderIndexMap() {
-  class RecordingTraversal : public ASTWalker {
-  public:
-    llvm::DenseMap<Expr *, unsigned> &IndexMap;
-    unsigned Index = 0;
-
-    explicit RecordingTraversal(llvm::DenseMap<Expr *, unsigned> &indexMap)
-      : IndexMap(indexMap) { }
-
-    std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
-      IndexMap[E] = Index;
-      Index++;
-      return { true, E };
-    }
-  };
-
-  llvm::DenseMap<Expr *, unsigned> indexMap;
-  RecordingTraversal traversal(indexMap);
-  walk(traversal);
-  return indexMap;
-}
-
 //===----------------------------------------------------------------------===//
 // Support methods for Exprs.
 //===----------------------------------------------------------------------===//

lib/Sema/ConstraintSystem.cpp

@@ -2727,6 +2727,29 @@ static DeclName getOverloadChoiceName(ArrayRef<OverloadChoice> choices) {
   return name;
 }
 
+/// Extend the given index map with all of the subexpressions in the given
+/// expression.
+static void extendPreorderIndexMap(
+    Expr *expr, llvm::DenseMap<Expr *, unsigned> &indexMap) {
+  class RecordingTraversal : public ASTWalker {
+  public:
+    llvm::DenseMap<Expr *, unsigned> &IndexMap;
+    unsigned Index = 0;
+
+    explicit RecordingTraversal(llvm::DenseMap<Expr *, unsigned> &indexMap)
+      : IndexMap(indexMap) { }
+
+    std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
+      IndexMap[E] = Index;
+      Index++;
+      return { true, E };
+    }
+  };
+
+  RecordingTraversal traversal(indexMap);
+  expr->walk(traversal);
+}
+
 bool ConstraintSystem::diagnoseAmbiguity(Expr *expr,
                                          ArrayRef<Solution> solutions) {
   // Produce a diff of the solutions.
@@ -2747,7 +2770,10 @@ bool ConstraintSystem::diagnoseAmbiguity(Expr *expr,
   // Heuristically, all other things being equal, we should complain about the
   // ambiguous expression that (1) has the most overloads, (2) is deepest, or
   // (3) comes earliest in the expression.
-  auto indexMap = expr->getPreorderIndexMap();
+  llvm::DenseMap<Expr *, unsigned> indexMap;
+  for (auto expr : InputExprs) {
+    extendPreorderIndexMap(expr, indexMap);
+  }
 
   for (unsigned i = 0, n = diff.overloads.size(); i != n; ++i) {
     auto &overload = diff.overloads[i];