Merge pull request swiftlang#66319 from DougGregor/cxx-import-field-caching

[Clang importer] Eliminate redundant imports of C++ fields as properties

Author: swift-ci

lib/ClangImporter/ClangImporter.cpp

@@ -5006,7 +5006,8 @@ DeclAttributes cloneImportedAttributes(ValueDecl *decl, ASTContext &context) {
   return attrs;
 }
 
-ValueDecl *cloneBaseMemberDecl(ValueDecl *decl, DeclContext *newContext) {
+static ValueDecl *
+cloneBaseMemberDecl(ValueDecl *decl, DeclContext *newContext) {
   if (auto fn = dyn_cast<FuncDecl>(decl)) {
     // TODO: function templates are specialized during type checking so to
     // support these we need to tell Swift to type check the synthesized bodies.
@@ -6290,16 +6291,23 @@ Decl *ClangImporter::importDeclDirectly(const clang::NamedDecl *decl) {
   return Impl.importDecl(decl, Impl.CurrentVersion);
 }
 
-ValueDecl *ClangImporter::importBaseMemberDecl(ValueDecl *decl,
-                                               DeclContext *newContext) {
+ValueDecl *ClangImporter::Implementation::importBaseMemberDecl(
+    ValueDecl *decl, DeclContext *newContext) {
   // Make sure we don't clone the decl again for this class, as that would
   // result in multiple definitions of the same symbol.
   std::pair<ValueDecl *, DeclContext *> key = {decl, newContext};
-  if (!Impl.clonedBaseMembers.count(key)) {
+  auto known = clonedBaseMembers.find(key);
+  if (known == clonedBaseMembers.end()) {
     ValueDecl *cloned = cloneBaseMemberDecl(decl, newContext);
-    Impl.clonedBaseMembers[key] = cloned;
+    known = clonedBaseMembers.insert({key, cloned}).first;
   }
-  return Impl.clonedBaseMembers[key];
+
+  return known->second;
+}
+
+ValueDecl *ClangImporter::importBaseMemberDecl(ValueDecl *decl,
+                                               DeclContext *newContext) {
+  return Impl.importBaseMemberDecl(decl, newContext);
 }
 
 void ClangImporter::diagnoseTopLevelValue(const DeclName &name) {

lib/ClangImporter/ImportDecl.cpp

@@ -3581,6 +3581,12 @@ namespace {
       if (!dc)
         return nullptr;
 
+      // While importing the DeclContext, we might have imported the decl
+      // itself.
+      auto known = Impl.importDeclCached(decl, getVersion());
+      if (known.has_value())
+        return known.value();
+
       // TODO: do we want to emit a diagnostic here?
       // Types that are marked as foreign references cannot be stored by value.
       if (auto recordType =
@@ -8761,8 +8767,6 @@ static void loadAllMembersOfSuperclassIfNeeded(ClassDecl *CD) {
     E->loadAllMembers();
 }
 
-ValueDecl *cloneBaseMemberDecl(ValueDecl *decl, DeclContext *newContext);
-
 void ClangImporter::Implementation::loadAllMembersOfRecordDecl(
     NominalTypeDecl *swiftDecl, const clang::RecordDecl *clangRecord) {
   // Import all of the members.
@@ -8793,7 +8797,7 @@ void ClangImporter::Implementation::loadAllMembersOfRecordDecl(
     // This means we found a member in a C++ record's base class.
     if (swiftDecl->getClangDecl() != clangRecord) {
       // So we need to clone the member into the derived class.
-      if (auto newDecl = cloneBaseMemberDecl(cast<ValueDecl>(member), swiftDecl)) {
+      if (auto newDecl = importBaseMemberDecl(cast<ValueDecl>(member), swiftDecl)) {
         swiftDecl->addMember(newDecl);
       }
       continue;

lib/ClangImporter/ImporterImpl.h

@@ -642,10 +642,14 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
   llvm::MapVector<std::pair<NominalTypeDecl *, Type>,
                   std::pair<FuncDecl *, FuncDecl *>> cxxSubscripts;
 
+private:
   // Keep track of the decls that were already cloned for this specific class.
   llvm::DenseMap<std::pair<ValueDecl *, DeclContext *>, ValueDecl *>
       clonedBaseMembers;
 
+  ValueDecl *importBaseMemberDecl(ValueDecl *decl, DeclContext *newContext);
+
+public:
   // Cache for already-specialized function templates and any thunks they may
   // have.
   llvm::DenseMap<clang::FunctionDecl *, ValueDecl *>