Add support for remembering origins to ExternalASTMerger

[spyffe]

Summary

ExternalASTMerger has hitherto relied on being able to look up any Decl through its named DeclContext chain. This works for many cases, but causes problems for function-local structs, which cannot be looked up in their containing FunctionDecl. An example case is

void f() {
  { struct S { int a; }; }
  { struct S { bool b; }; }
}

It is not possible to lookup either of the two Ses individually (or even to provide enough information to disambiguate) after parsing is over; and there is typically no need to, since they are invisible to the outside world.

However, ExternalASTMerger needs to be able to complete either S on demand. This led to an XFAIL on test/Import/local-struct, which this patch removes. The way the patch works is:

• It defines a new data structure, ExternalASTMerger::OriginMap, which clients are expected to maintain (default-constructing if the origin does not have an ExternalASTMerger servicing it)
• As DeclContexts are imported, if they cannot be looked up by name they are placed in the OriginMap. This allows ExternalASTMerger to complete them later if necessary.
• As DeclContexts are imported from an origin that already has its own OriginMap, the origins are forwarded – but only for those DeclContexts that are actually used. This keeps the amount of stored data minimal.

[spyffe]

Updated the patch to eliminate the need to pass in an OriginMap for the target. The OriginMap can be extracted afterward, and merged by other algorithms if necessary.

[spyffe]

Updated the patch to make it possible for external clients to record the origins of types manually, a requirement for LLDB.

[spyffe]

Added more tests, and added an option to clang-import-test to actually use the origin-forwarding code. Also fixed some errors in CompleteType that were caught by these new tests.

[spyffe]

Removed unnecessary code and improved code coverage. Also made a few operational changes:

• In initial lookup, accept forward declarations. They can be completed later.
• When doing lookup in a DeclContext, only look at source DeclContexts of the same type.
• Assume that only Decls with hasExternalLexicalStorage are actually completed, saving runtime and simplifying the code. Fixed one case in Sema where this rule was violated.

[spyffe]

Added DEBUG_PRINTF code to enable introspection into what's happening.

[bruno]

Hi Sean,

Thanks for making this functionality available in clang. Comments below.

Can you please add cfe-commits to the review for the next round?

include/clang/AST/ExternalASTMerger.h

60–66

Please add a comment explaining what Origins means and what it's used for.

81

Cool, I like these abstraction more than ImporterEndpoint. Please add comments explaining what ImporterTarget and ImporterSource represent in this context.

lib/AST/ExternalASTMerger.cpp

21

This seems brittle. Maybe hide this logic behind a variable that can be setup through clang-importer-test invocation by passing down a flag? Another solution is to hide users on dump functions, along the line of AST dumpers, etc.

35–36

Please add a comment explaining what do you mean by canonicalization here.

71

Why is it best to rely on the Origins map?

83–84

Add some comments on why you need a LazyASTImporter, so users know what to expect. Is LazyASTImporter expected to have other users outside this in the future? I wonder if it's worth to have this in ExternalASTMerger.h or any other place.

84

Odd identation here.

97

Please add a comment explaining what this method does.

99

This doesn't seem to be clang-formatted.

102

merger -> Merger

104

Same here!

107

Same here! And all the other places.

114

auto SourceDC -> auto *SourceDC

195

What's the deal with this commented out snippet?

203

auto T1 -> auto *T1

204

auto T2 -> auto *T2, please also fix other places with * or & where appropriate.

206

This is an example of where having a variable for conditionally printing extra information becomes handy.

229

No need for curly braces here.

[spyffe]

Updated to reflect Bruno's suggestions.

• Commented ExternalASTMerger.h extensively.
• Refactored the log into a pluggable raw_ostream that defaults to llvm::nulls().
• Added comments per Bruno's requests
• Fixed some indentation
• Fixed some variable names and auto [*&] s
• Removed some commented-out code
• Cleaned up some curly braces

[bruno]

Thanks for the additional docs! More comments below.

lib/AST/ExternalASTMerger.cpp

116

Can you conditionalize the logging?

126

Same here.

134

Same here.

213

Same here.

286

Ditto

292

Ditto

tools/clang-import-test/clang-import-test.cpp

232

Can you also add a brief documentation for this one?

242

No need for the else here.

256

No need for curly braces here.

326

No need for the else here.

333

No need for curly braces here.

354

No need for the else here.

365

No need for braces in this entire block

376

No need for the else here.

[spyffe]

At @bruno 's request, abandoning this revision in favor of the updated https://reviews.llvm.org/D38208.
That revision has all the changes requested.

include/clang/AST/ExternalASTMerger.h

 //  from several different ASTContext/FileManager pairs
 //
 //===----------------------------------------------------------------------===//
 #ifndef LLVM_CLANG_AST_EXTERNALASTMERGER_H
 #define LLVM_CLANG_AST_EXTERNALASTMERGER_H
 
 #include "clang/AST/ASTImporter.h"
 #include "clang/AST/ExternalASTSource.h"
+#include "llvm/Support/raw_ostream.h"
 
 namespace clang {
 
+/// ExternalASTSource implementation that merges information from several
+/// ASTContexts.
+///
+/// ExtermalASTMerger maintains a vector of ASTImporters that it uses to import
+/// (potentially incomplete) Decls and DeclContexts from the source ASTContexts
+/// in response to ExternalASTSource API calls.
+///
+/// When lookup occurs in the resulting imported DeclContexts, the original
+/// DeclContexts need to be queried.  Roughly, there are three cases here:
+///
+/// - The DeclContext of origin can be found by simple name lookup.  In this
+///   case, no additional state is required.
+///
+/// - The DeclContext of origin is different from what would be found by name
+///   lookup.  In this case, Origins contains an entry overriding lookup and
+///   specifying the correct pair of DeclContext/ASTContext.
+///
+/// - The DeclContext of origin was determined by another ExterenalASTMerger. 
+///   (This is possible when the source ASTContext for one of the Importers has
+///   its own ExternalASTMerger).  The origin must be properly forwarded in this
+///   case.
+///
+/// ExternalASTMerger's job is to maintain the data structures necessary to
+/// allow this.  The data structures themselves can be extracted (read-only) and
+/// copied for re-use.
 class ExternalASTMerger : public ExternalASTSource {
 public:
-  struct ImporterPair {
-    std::unique_ptr<ASTImporter> Forward;
-    std::unique_ptr<ASTImporter> Reverse;
+  /// A single origin for a DeclContext.  Unlike Decls, DeclContexts do
+  /// not allow their containing ASTContext to be determined in all cases.
+  struct DCOrigin {
+    DeclContext *DC;
+    ASTContext *AST;
   };
 
+  typedef std::map<const DeclContext *, DCOrigin> OriginMap;
+  typedef std::vector<std::unique_ptr<ASTImporter>> ImporterVector;
 private:
-  std::vector<ImporterPair> Importers;
+  /// One importer exists for each source.  
+  ImporterVector Importers;
+  /// Overrides in case name lookup would return nothing or would return
+  /// the wrong thing.
+  OriginMap Origins;
+  /// The installed log stream.
+  llvm::raw_ostream *LogStream;
 
 public:
-  struct ImporterEndpoint {
+  /// The target for an ExternalASTMerger.
+  ///
+  /// ASTImporters require both ASTContext and FileManager to be able to
+  /// import SourceLocations properly.
+  struct ImporterTarget {
     ASTContext &AST;
     FileManager &FM;
   };
-  ExternalASTMerger(const ImporterEndpoint &Target,
-                    llvm::ArrayRef<ImporterEndpoint> Sources);
+  /// A source for an ExternalASTMerger.
+  ///
+  /// ASTImporters require both ASTContext and FileManager to be able to
+  /// import SourceLocations properly.  Additionally, when import occurs for
+  /// a DeclContext whose origin has been overridden, then this
+  /// ExternalASTMerger must be able to determine that.
+  struct ImporterSource {
+    ASTContext &AST;
+    FileManager &FM;
+    const OriginMap &OM;
+  };
 
+private:
+  /// The target for this ExtenralASTMerger.
+  ImporterTarget Target;
+
+public:
+  ExternalASTMerger(const ImporterTarget &Target,
+                    llvm::ArrayRef<ImporterSource> Sources);
+
+  /// Add a set of ASTContexts as possible origins.
+  ///
+  /// Usually the set will be initialized in the constructor, but long-lived
+  /// ExternalASTMergers may neeed to import from new sources (for example,
+  /// newly-parsed source files).
+  ///
+  /// Ensures that Importers does not gain duplicate entries as a result.
+  void AddSources(llvm::ArrayRef<ImporterSource> Sources);
+
+  /// Remove a set of ASTContexts as possible origins.
+  ///
+  /// Sometimes an origin goes away (for example, if a source file gets
+  /// superseded by a newer version). 
+  ///
+  /// The caller is responsible for ensuring that this doesn't leave
+  /// DeclContexts that can't be completed.
+  void RemoveSources(llvm::ArrayRef<ImporterSource> Sources);
+
+  /// Implementation of the ExternalASTSource API.
   bool FindExternalVisibleDeclsByName(const DeclContext *DC,
                                       DeclarationName Name) override;
 
+  /// Implementation of the ExternalASTSource API.
   void
   FindExternalLexicalDecls(const DeclContext *DC,
                            llvm::function_ref<bool(Decl::Kind)> IsKindWeWant,
                            SmallVectorImpl<Decl *> &Result) override;
+
+  /// Implementation of the ExternalASTSource API.
+  void CompleteType(TagDecl *Tag) override;
+
+  /// Implementation of the ExternalASTSource API.
+  void CompleteType(ObjCInterfaceDecl *Interface) override;
+
+  /// Returns true if DC can be found in any source AST context.
+  bool CanComplete(DeclContext *DC);
+
+  /// Records an origin in Origins only if name lookup would find
+  /// something different or nothing at all.
+  void MaybeRecordOrigin(const DeclContext *ToDC, DCOrigin Origin);
+
+  /// Regardless of any checks, override the Origin for a DeclContext.
+  void ForceRecordOrigin(const DeclContext *ToDC, DCOrigin Origin);
+
+  /// Get a read-only view of the Origins map, for use in constructing
+  /// an ImporterSource for another ExternalASTMerger.
+  const OriginMap &GetOrigins() { return Origins; }
+
+  /// Returns true if Importers contains an ASTImporter whose source is
+  /// OriginContext.
+  bool HasImporterForOrigin(ASTContext &OriginContext);
+
+  /// Returns a reference to the ASTRImporter from Importers whose origin
+  /// is OriginContext.  This allows manual import of ASTs while preserving the
+  /// OriginMap correctly.
+  ASTImporter &ImporterForOrigin(ASTContext &OriginContext);
+
+  /// Sets the current log stream.
+  void SetLogStream(llvm::raw_string_ostream &Stream) { LogStream = &Stream; }
+private:
+  /// Records and origin in Origins.
+  void RecordOriginImpl(const DeclContext *ToDC, DCOrigin Origin,
+                                  ASTImporter &importer);
+
+  /// Performs an action for every DeclContext that is identified as
+  /// corresponding (either by forced origin or by name lookup) to DC.
+  template <typename CallbackType>
+  void ForEachMatchingDC(const DeclContext *DC, CallbackType Callback);
+
+public: 
+  /// Log something if there is a logging callback installed.
+  llvm::raw_ostream &logs() { return *LogStream; }
+
+  /// True if the log stream is not llvm::nulls();
+  bool LoggingEnabled() { return LogStream != &llvm::nulls(); }
 };
 
 } // end namespace clang
 
 #endif

lib/AST/ExternalASTMerger.cpp

 //===- ExternalASTMerger.cpp - Merging External AST Interface ---*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 //  This file implements the ExternalASTMerger, which vends a combination of
 //  ASTs from several different ASTContext/FileManager pairs
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
+#include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/ExternalASTMerger.h"
 
 using namespace clang;
 
 namespace {
 
 template <typename T> struct Source {
   T t;
   Source(T t) : t(t) {}
   operator T() { return t; }
   template <typename U = T> U &get() { return t; }
   template <typename U = T> const U &get() const { return t; }
   template <typename U> operator Source<U>() { return Source<U>(t); }
 };
 
 typedef std::pair<Source<NamedDecl *>, ASTImporter *> Candidate;
 
-class LazyASTImporter : public ASTImporter {
-public:
-  LazyASTImporter(ASTContext &ToContext, FileManager &ToFileManager,
-                  ASTContext &FromContext, FileManager &FromFileManager)
-      : ASTImporter(ToContext, ToFileManager, FromContext, FromFileManager,
-                    /*MinimalImport=*/true) {}
-  Decl *Imported(Decl *From, Decl *To) override {
-    if (auto ToTag = dyn_cast<TagDecl>(To)) {
-      ToTag->setHasExternalLexicalStorage();
-      ToTag->setMustBuildLookupTable();
-    } else if (auto ToNamespace = dyn_cast<NamespaceDecl>(To)) {
-      ToNamespace->setHasExternalVisibleStorage();
-    } else if (auto ToContainer = dyn_cast<ObjCContainerDecl>(To)) {
-      ToContainer->setHasExternalLexicalStorage();
-      ToContainer->setMustBuildLookupTable();
-    }
-    return ASTImporter::Imported(From, To);
-  }
-};
+/// For the given DC, return the DC that is safe to perform lookups on.  This is
+/// the DC we actually want to work with most of the time.
+const DeclContext *CanonicalizeDC(const DeclContext *DC) {
+  if (isa<LinkageSpecDecl>(DC))
+    return DC->getRedeclContext();
+  return DC;
 
 Source<const DeclContext *>
 LookupSameContext(Source<TranslationUnitDecl *> SourceTU, const DeclContext *DC,
                   ASTImporter &ReverseImporter) {
+  DC = CanonicalizeDC(DC);
   if (DC->isTranslationUnit()) {
     return SourceTU;
   }
   Source<const DeclContext *> SourceParentDC =
       LookupSameContext(SourceTU, DC->getParent(), ReverseImporter);
   if (!SourceParentDC) {
     // If we couldn't find the parent DC in this TranslationUnit, give up.
     return nullptr;
   }
-  auto ND = cast<NamedDecl>(DC);
+  auto *ND = cast<NamedDecl>(DC);
   DeclarationName Name = ND->getDeclName();
   Source<DeclarationName> SourceName = ReverseImporter.Import(Name);
   DeclContext::lookup_result SearchResult =
       SourceParentDC.get()->lookup(SourceName.get());
   size_t SearchResultSize = SearchResult.size();
-  // Handle multiple candidates once we have a test for it.
-  // This may turn up when we import template specializations correctly.
-  assert(SearchResultSize < 2);
-  if (SearchResultSize == 0) {
-    // couldn't find the name, so we have to give up
+  if (SearchResultSize == 0 || SearchResultSize > 1) {
+    // There are two cases here.  First, we might not find the name.
+    // We might also find multiple copies, in which case we have no
+    // guarantee that the one we wanted is the one we pick.  (E.g.,
+    // if we have two specializations of the same template it is
+    // very hard to determine which is the one you want.)
+    //
+    // The Origins map fixes this problem by allowing the origin to be
+    // explicitly recorded, so we trigger that recording by returning
+    // nothing (rather than a possibly-inaccurate guess) here.
     return nullptr;
   } else {
     NamedDecl *SearchResultDecl = SearchResult[0];
-    return dyn_cast<DeclContext>(SearchResultDecl);
+    if (isa<DeclContext>(SearchResultDecl) &&
+        SearchResultDecl->getKind() == DC->getDeclKind())
+      return cast<DeclContext>(SearchResultDecl)->getPrimaryContext();
+    else
+      return nullptr; // This type of lookup is unsupported
   }
 }
 
-bool IsForwardDeclaration(Decl *D) {
-  if (auto TD = dyn_cast<TagDecl>(D)) {
-    return !TD->isThisDeclarationADefinition();
-  } else if (auto FD = dyn_cast<FunctionDecl>(D)) {
-    return !FD->isThisDeclarationADefinition();
-  } else if (auto OID = dyn_cast<ObjCInterfaceDecl>(D)) {
-     return OID->isThisDeclarationADefinition();
+/// A custom implementation of ASTImporter, for ExternalASTMerger's purposes.
+///
+/// There are several modifications:
+///
+/// - It enables lazy lookup (via the HasExternalLexicalStorage flag and a few
+///   others), which instructs Clang to refer to ExternalASTMerger.  Also, it
+///   forces MinimalImport to true, which is necessary to make this work.
+/// - It maintains a reverse importer for use with names.  This allows lookup of
+///   arbitrary names in the source context.
+/// - It updates the ExternalASTMerger's origin map as needed whenever a
+///   it sees a DeclContext.
+class LazyASTImporter : public ASTImporter {
+private:
+  ExternalASTMerger &Parent;
+  ASTImporter Reverse;
+  const ExternalASTMerger::OriginMap &FromOrigins;
+
+  llvm::raw_ostream &logs() { return Parent.logs(); }
+public:
+  LazyASTImporter(ExternalASTMerger &_Parent, ASTContext &ToContext,
+                  FileManager &ToFileManager, ASTContext &FromContext,
+                  FileManager &FromFileManager,
+                  const ExternalASTMerger::OriginMap &_FromOrigins)
+      : ASTImporter(ToContext, ToFileManager, FromContext, FromFileManager,
+                    /*MinimalImport=*/true),
+        Parent(_Parent), Reverse(FromContext, FromFileManager, ToContext,
+                                 ToFileManager, /*MinimalImport=*/true), FromOrigins(_FromOrigins) {}
+
+  /// Whenever a DeclContext is imported, ensure that ExternalASTSource's origin
+  /// map is kept up to date.  Also set the appropriate flags.
+  Decl *Imported(Decl *From, Decl *To) override {
+    if (auto *ToDC = dyn_cast<DeclContext>(To)) {
+      logs() << "(ExternalASTMerger*)" << (void*)&Parent
+             << " imported (DeclContext*)" << (void*)ToDC
+             << ", (ASTContext*)" << (void*)&getToContext()
+             << " from (DeclContext*)" << (void*)llvm::cast<DeclContext>(From)
+             << ", (ASTContext*)" << (void*)&getFromContext()
+             << "\n";
+      Source<DeclContext *> FromDC(
+          cast<DeclContext>(From)->getPrimaryContext());
+      if (FromOrigins.count(FromDC) &&
+          Parent.HasImporterForOrigin(*FromOrigins.at(FromDC).AST)) {
+        logs() << "(ExternalASTMerger*)" << (void*)&Parent
+               << " forced origin (DeclContext*)"
+               << (void*)FromOrigins.at(FromDC).DC
+               << ", (ASTContext*)"
+               << (void*)FromOrigins.at(FromDC).AST
+               << "\n";
+        Parent.ForceRecordOrigin(ToDC, FromOrigins.at(FromDC));
       } else {
+        logs() << "(ExternalASTMerger*)" << (void*)&Parent
+               << " maybe recording origin (DeclContext*)" << (void*)FromDC
+               << ", (ASTContext*)" << (void*)&getFromContext()
+               << "\n";
+        Parent.MaybeRecordOrigin(ToDC, {FromDC, &getFromContext()});
+      }
+    }
+    if (auto *ToTag = dyn_cast<TagDecl>(To)) {
+      ToTag->setHasExternalLexicalStorage();
+      ToTag->setMustBuildLookupTable();
+      assert(Parent.CanComplete(ToTag));
+    } else if (auto *ToNamespace = dyn_cast<NamespaceDecl>(To)) {
+      ToNamespace->setHasExternalVisibleStorage();
+      assert(Parent.CanComplete(ToNamespace));
+    } else if (auto *ToContainer = dyn_cast<ObjCContainerDecl>(To)) {
+      ToContainer->setHasExternalLexicalStorage();
+      ToContainer->setMustBuildLookupTable();
+      assert(Parent.CanComplete(ToContainer));
+    }
+    return ASTImporter::Imported(From, To);
+  }
+  ASTImporter &GetReverse() { return Reverse; }
+};
+
+bool HasDeclOfSameType(llvm::ArrayRef<Candidate> Decls, const Candidate &C) {
+  if (isa<FunctionDecl>(C.first.get()))
     return false;
+  return llvm::any_of(Decls, [&](const Candidate &D) {
+    return C.first.get()->getKind() == D.first.get()->getKind();
+  });
+}
+
+} // end namespace
+
+ASTImporter &ExternalASTMerger::ImporterForOrigin(ASTContext &OriginContext) {
+  for (const std::unique_ptr<ASTImporter> &I : Importers) {
+    if (&I->getFromContext() == &OriginContext)
+      return *I;
+  }
+  llvm_unreachable("We should have an importer for this origin!");
+}
+
+namespace {
+LazyASTImporter &LazyImporterForOrigin(ExternalASTMerger &Merger,
+                                   ASTContext &OriginContext) {
+  return static_cast<LazyASTImporter &>(
+      Merger.ImporterForOrigin(OriginContext));
+}
+}
+
+bool ExternalASTMerger::HasImporterForOrigin(ASTContext &OriginContext) {
+  for (const std::unique_ptr<ASTImporter> &I : Importers) {
+    if (&I->getFromContext() == &OriginContext)
+      return true;
   }
+  return false;
 }
 
 template <typename CallbackType>
-void ForEachMatchingDC(
-    const DeclContext *DC,
-    llvm::ArrayRef<ExternalASTMerger::ImporterPair> Importers,
+void ExternalASTMerger::ForEachMatchingDC(const DeclContext *DC,
                                           CallbackType Callback) {
-  for (const ExternalASTMerger::ImporterPair &IP : Importers) {
+  if (Origins.count(DC)) {
+    ExternalASTMerger::DCOrigin Origin = Origins[DC];
+    LazyASTImporter &Importer = LazyImporterForOrigin(*this, *Origin.AST);
+    Callback(Importer, Importer.GetReverse(), Origin.DC);
+  } else {
+    bool DidCallback = false;
+    for (const std::unique_ptr<ASTImporter> &Importer : Importers) {
       Source<TranslationUnitDecl *> SourceTU =
-        IP.Forward->getFromContext().getTranslationUnitDecl();
-    if (auto SourceDC = LookupSameContext(SourceTU, DC, *IP.Reverse))
-      Callback(IP, SourceDC);
+          Importer->getFromContext().getTranslationUnitDecl();
+      ASTImporter &Reverse =
+          static_cast<LazyASTImporter *>(Importer.get())->GetReverse();
+      if (auto SourceDC = LookupSameContext(SourceTU, DC, Reverse)) {
+        DidCallback = true;
+        if (Callback(*Importer, Reverse, SourceDC))
+          break;
+      }
+    }
+    if (!DidCallback)
+      logs() << "(ExternalASTMerger*)" << (void*)this
+             << " asserting for (DeclContext*)" << (void*)DC
+             << ", (ASTContext*)" << (void*)&Target.AST
+             << "\n";
+    assert(DidCallback && "Couldn't find a source context matching our DC");
   }
 }
 
-bool HasDeclOfSameType(llvm::ArrayRef<Candidate> Decls, const Candidate &C) {
-  return llvm::any_of(Decls, [&](const Candidate &D) {
-    return C.first.get()->getKind() == D.first.get()->getKind();
+void ExternalASTMerger::CompleteType(TagDecl *Tag) {
+  assert(Tag->hasExternalLexicalStorage());
+  ForEachMatchingDC(Tag, [&](ASTImporter &Forward, ASTImporter &Reverse,
+                             Source<const DeclContext *> SourceDC) -> bool {
+    auto *SourceTag = const_cast<TagDecl *>(cast<TagDecl>(SourceDC.get()));
+    if (SourceTag->hasExternalLexicalStorage())
+      SourceTag->getASTContext().getExternalSource()->CompleteType(SourceTag);
+    if (!SourceTag->getDefinition())
+      return false;
+    Forward.Imported(SourceTag, Tag);
+    Forward.ImportDefinition(SourceTag);
+    Tag->setCompleteDefinition(SourceTag->isCompleteDefinition());
+    return true;
   });
 }
-} // end namespace
 
-ExternalASTMerger::ExternalASTMerger(const ImporterEndpoint &Target,
-                                     llvm::ArrayRef<ImporterEndpoint> Sources) {
-  for (const ImporterEndpoint &S : Sources) {
-    Importers.push_back(
-        {llvm::make_unique<LazyASTImporter>(Target.AST, Target.FM, S.AST, S.FM),
-         llvm::make_unique<ASTImporter>(S.AST, S.FM, Target.AST, Target.FM,
-                                        /*MinimalImport=*/true)});
+void ExternalASTMerger::CompleteType(ObjCInterfaceDecl *Interface) {
+  assert(Interface->hasExternalLexicalStorage());
+  ForEachMatchingDC(
+      Interface, [&](ASTImporter &Forward, ASTImporter &Reverse,
+                     Source<const DeclContext *> SourceDC) -> bool {
+        auto *SourceInterface = const_cast<ObjCInterfaceDecl *>(
+            cast<ObjCInterfaceDecl>(SourceDC.get()));
+        if (SourceInterface->hasExternalLexicalStorage())
+          SourceInterface->getASTContext().getExternalSource()->CompleteType(
+              SourceInterface);
+        if (!SourceInterface->getDefinition())
+          return false;
+        Forward.Imported(SourceInterface, Interface);
+        Forward.ImportDefinition(SourceInterface);
+        return true;
+      });
+}
+
+bool ExternalASTMerger::CanComplete(DeclContext *Interface) {
+  assert(Interface->hasExternalLexicalStorage() ||
+         Interface->hasExternalVisibleStorage());
+  bool FoundMatchingDC = false;
+  ForEachMatchingDC(Interface,
+                    [&](ASTImporter &Forward, ASTImporter &Reverse,
+                        Source<const DeclContext *> SourceDC) -> bool {
+                      FoundMatchingDC = true;
+                      return true;
+                    });
+  return FoundMatchingDC;
+}
+
+namespace {
+bool IsSameDC(const DeclContext *D1, const DeclContext *D2) {
+  if (isa<ObjCContainerDecl>(D1) && isa<ObjCContainerDecl>(D2))
+    return true; // There are many cases where Objective-C is ambiguous.
+  if (auto *T1 = dyn_cast<TagDecl>(D1))
+    if (auto *T2 = dyn_cast<TagDecl>(D2))
+      if (T1->getFirstDecl() == T2->getFirstDecl())
+        return true;
+  return D1 == D2 || D1 == CanonicalizeDC(D2);
+}
+}
+
+void ExternalASTMerger::MaybeRecordOrigin(const DeclContext *ToDC, DCOrigin Origin) {
+  LazyASTImporter &Importer = LazyImporterForOrigin(*this, *Origin.AST);
+  ASTImporter &Reverse = Importer.GetReverse();
+  Source<const DeclContext *> FoundFromDC =
+      LookupSameContext(Origin.AST->getTranslationUnitDecl(), ToDC, Reverse);
+  if (!FoundFromDC || !IsSameDC(FoundFromDC.get(), Origin.DC)) {
+    logs() << "(ExternalASTMerger*)" << (void*)this
+           << " decided to record origin (DeclContext*)" << (void*)Origin.DC
+           << ", (ASTContext*)" << (void*)&Origin.AST
+           << "\n";
+    RecordOriginImpl(ToDC, Origin, Importer);
+  } else {
+    logs() << "(ExternalASTMerger*)" << (void*)this
+           << " decided NOT to record origin (DeclContext*)" << (void*)Origin.DC
+           << ", (ASTContext*)" << (void*)&Origin.AST
+           << "\n";
+  }
+}
+
+void ExternalASTMerger::ForceRecordOrigin(const DeclContext *ToDC,
+                                          DCOrigin Origin) {
+  RecordOriginImpl(ToDC, Origin, ImporterForOrigin(*Origin.AST));
+}
+
+void ExternalASTMerger::RecordOriginImpl(const DeclContext *ToDC, DCOrigin Origin,
+                                         ASTImporter &Importer) {
+  Origins[ToDC] = Origin;
+  Importer.ASTImporter::Imported(cast<Decl>(Origin.DC), const_cast<Decl*>(cast<Decl>(ToDC)));
+}
+
+ExternalASTMerger::ExternalASTMerger(const ImporterTarget &Target,
+                                     llvm::ArrayRef<ImporterSource> Sources) : LogStream(&llvm::nulls()), Target(Target) {
+  AddSources(Sources);
+}
+
+void ExternalASTMerger::AddSources(llvm::ArrayRef<ImporterSource> Sources) {
+  for (const ImporterSource &S : Sources) {
+    assert(&S.AST != &Target.AST);
+    Importers.push_back(llvm::make_unique<LazyASTImporter>(
+        *this, Target.AST, Target.FM, S.AST, S.FM, S.OM));
+  }
+}
+
+void ExternalASTMerger::RemoveSources(llvm::ArrayRef<ImporterSource> Sources) {
+  if (LoggingEnabled())
+    for (const ImporterSource &S : Sources)
+      logs() << "(ExternalASTMerger*)" << (void*)this
+             << " removing source (ASTContext*)" << (void*)&S.AST
+             << "\n";
+  Importers.erase(
+      std::remove_if(Importers.begin(), Importers.end(),
+                     [&Sources](std::unique_ptr<ASTImporter> &Importer) -> bool {
+                       for (const ImporterSource &S : Sources) {
+                         if (&Importer->getFromContext() == &S.AST)
+                           return true;
+                       }
+                       return false;
+                     }),
+      Importers.end());
+  for (OriginMap::iterator OI = Origins.begin(), OE = Origins.end(); OI != OE; ) {
+    std::pair<const DeclContext *, DCOrigin> Origin = *OI;
+    bool Erase = false;
+    for (const ImporterSource &S : Sources) {
+      if (&S.AST == Origin.second.AST) {
+        Erase = true;
+        break;
+      }
+    }
+    if (Erase)
+      OI = Origins.erase(OI);
+    else
+      ++OI;
   }
 }
 
 bool ExternalASTMerger::FindExternalVisibleDeclsByName(const DeclContext *DC,
                                                        DeclarationName Name) {
   llvm::SmallVector<NamedDecl *, 1> Decls;
-  llvm::SmallVector<Candidate, 4> CompleteDecls;
-  llvm::SmallVector<Candidate, 4> ForwardDecls;
+  llvm::SmallVector<Candidate, 4> Candidates;
 
-  auto FilterFoundDecl = [&CompleteDecls, &ForwardDecls](const Candidate &C) {
-    if (IsForwardDeclaration(C.first.get())) {
-      if (!HasDeclOfSameType(ForwardDecls, C)) {
-        ForwardDecls.push_back(C);
-      }
-    } else {
-      CompleteDecls.push_back(C);
-    }
+  auto FilterFoundDecl = [&Candidates](const Candidate &C) {
+   if (!HasDeclOfSameType(Candidates, C))
+     Candidates.push_back(C);
   };
 
-  ForEachMatchingDC(
-      DC, Importers,
-      [&](const ImporterPair &IP, Source<const DeclContext *> SourceDC) {
-        DeclarationName FromName = IP.Reverse->Import(Name);
-        DeclContextLookupResult Result = SourceDC.get()->lookup(FromName);
-        for (NamedDecl *FromD : Result) {
-          FilterFoundDecl(std::make_pair(FromD, IP.Forward.get()));
-        }
-      });
+  ForEachMatchingDC(DC, [&](ASTImporter &Forward, ASTImporter &Reverse,
+                            Source<const DeclContext *> SourceDC) -> bool {
+    DeclarationName FromName = Reverse.Import(Name);
+      FilterFoundDecl(std::make_pair(FromD, &Forward));
+    return false;
 
-  llvm::ArrayRef<Candidate> DeclsToReport =
-      CompleteDecls.empty() ? ForwardDecls : CompleteDecls;
-
-  if (DeclsToReport.empty()) {
+  if (Candidates.empty()) {
     return false;
   }
 
-  Decls.reserve(DeclsToReport.size());
-  for (const Candidate &C : DeclsToReport) {
+  Decls.reserve(Candidates.size());
+  for (const Candidate &C : Candidates) {
     NamedDecl *d = cast<NamedDecl>(C.second->Import(C.first.get()));
     assert(d);
     Decls.push_back(d);
   }
   SetExternalVisibleDeclsForName(DC, Name, Decls);
   return true;
 }
 
 void ExternalASTMerger::FindExternalLexicalDecls(
     const DeclContext *DC, llvm::function_ref<bool(Decl::Kind)> IsKindWeWant,
     SmallVectorImpl<Decl *> &Result) {
-  ForEachMatchingDC(
-      DC, Importers,
-      [&](const ImporterPair &IP, Source<const DeclContext *> SourceDC) {
-        for (const Decl *SourceDecl : SourceDC.get()->decls()) {
-          if (IsKindWeWant(SourceDecl->getKind())) {
-            Decl *ImportedDecl =
-                IP.Forward->Import(const_cast<Decl *>(SourceDecl));
-            assert(ImportedDecl->getDeclContext() == DC);
-            (void)ImportedDecl;
-          }
-        }
-      });
+  ForEachMatchingDC(DC, [&](ASTImporter &Forward, ASTImporter &Reverse,
+                            Source<const DeclContext *> SourceDC) -> bool {
+        Decl *ImportedDecl = Forward.Import(const_cast<Decl *>(SourceDecl));
+        assert(!ImportedDecl || IsSameDC(ImportedDecl->getDeclContext(), DC));
+    return false;
 }
 

lib/Sema/SemaType.cpp

         Tag ? static_cast<NamedDecl *>(Tag->getDecl()) : IFace->getDecl();
 
     // Avoid diagnosing invalid decls as incomplete.
     if (D->isInvalidDecl())
       return true;
 
     // Give the external AST source a chance to complete the type.
     if (auto *Source = Context.getExternalSource()) {
-      if (Tag)
-        Source->CompleteType(Tag->getDecl());
-      else
-        Source->CompleteType(IFace->getDecl());
-
+      if (Tag) {
+        TagDecl *TagD = Tag->getDecl();
+        if (TagD->hasExternalLexicalStorage())
+          Source->CompleteType(TagD);
+      } else {
+        ObjCInterfaceDecl *IFaceD = IFace->getDecl();
+        if (IFaceD->hasExternalLexicalStorage())
+          Source->CompleteType(IFace->getDecl());
+      }
       // If the external source completed the type, go through the motions
       // again to ensure we're allowed to use the completed type.
       if (!T->isIncompleteType())
         return RequireCompleteTypeImpl(Loc, T, Diagnoser);
     }
   }
 
   // If we have a class template specialization or a class member of a

test/Import/extern-c-function/Inputs/F.cpp

-void f(int arg) { }
+extern "C" {
+  void f(int arg);
+}

test/Import/extern-c-function/test.cpp

-// RUN: clang-import-test -import %S/Inputs/F1.c -import %S/Inputs/F2.c -expression %s
+// RUN: clang-import-test -import %S/Inputs/F.cpp -expression %s
 void expr() {
   f(2);
-  f("world");
-  S s;
-  f(s);
-}
+}

test/Import/forward-declared-objc-class/Inputs/S1.m

-struct S;
+@class MyClass;
 No newline at end of file

test/Import/forward-declared-objc-class/Inputs/S2.m

-struct S {
-  int a;
+@interface MyClass {
+  int j;
 };
++(MyClass*)fromInteger:(int)_j;
+-(int)getInteger;
+@end
 No newline at end of file

test/Import/forward-declared-objc-class/Inputs/S3.m

-struct S;
+@class MyClass;
 No newline at end of file

test/Import/forward-declared-objc-class/test.m

-// RUN: clang-import-test -import %S/Inputs/S1.c --import %S/Inputs/S2.c -expression %s
+// RUN: clang-import-test -x objective-c++ -import %S/Inputs/S1.m --import %S/Inputs/S2.m --import %S/Inputs/S3.m -expression %s
 void expr() {
-  struct S MyS;
-  MyS.a = 3;
+  MyClass *c = [MyClass fromInteger:3];
+  const int i = [c getInteger];
+  const int j = c->j;
 }

test/Import/forward-declared-struct/test.c

-// RUN: clang-import-test -import %S/Inputs/S1.c --import %S/Inputs/S2.c -expression %s
+// RUN: clang-import-test -import %S/Inputs/S1.c --import %S/Inputs/S2.c --import %S/Inputs/S3.c -expression %s
 void expr() {
   struct S MyS;
   MyS.a = 3;
 }

test/Import/local-struct-use-origins/test.cpp

-// RUN: clang-import-test -dump-ir -import %S/Inputs/Callee.cpp -expression %s | FileCheck %s
-// XFAIL: *
+// RUN: clang-import-test -dump-ir -use-origins -import %S/Inputs/Callee.cpp -expression %s | FileCheck %s
 // CHECK: %struct.S = type { i
-// CHECK: %struct.S.0 = type { i1 }
+// CHECK: %struct.S.0 = type { i
 
 void foo() {
   return Bar().bar(3, true);
 }

test/Import/local-struct/test.cpp

 // RUN: clang-import-test -dump-ir -import %S/Inputs/Callee.cpp -expression %s | FileCheck %s
-// XFAIL: *
 // CHECK: %struct.S = type { i
-// CHECK: %struct.S.0 = type { i1 }
+// CHECK: %struct.S.0 = type { i
 
 void foo() {
   return Bar().bar(3, true);
 }

test/Import/objc-definitions-in-expression/test.m

 // RUN: clang-import-test -x objective-c++ -import %S/Inputs/S.m -expression %s
+@class D;
+
+@interface B {
+  int x;
+  int y;
+}
+@end
+
+@interface D : B {
+  int z;
+}
+-(int)n;
+@end
+
 void expr() {
   C *c;
   int i = [c m];
+  D *d;
+  int j = [d n] + d->x;
 }

test/Import/struct-and-var/Inputs/S1.cpp

-class T;
-
-class S {
-  T *t;
-  int a;
-};
+int F;

test/Import/struct-and-var/Inputs/S2.cpp

-class U {
-  int b;
-};
-
-class T {
-  U u;
+struct F {
+  int a;
 };

test/Import/struct-and-var/test.cpp

 // RUN: clang-import-test --import %S/Inputs/S1.cpp --import %S/Inputs/S2.cpp -expression %s
 void expr() {
-  S MyS;
-  T MyT;
-  MyS.a = 3;
-  MyT.u.b = 2;
+  struct F f;
+  int x = f.a;
 }

test/Import/template/Inputs/T.cpp

 template <typename T> struct A {
-};
-
-template <> struct A<int> {
-  struct B {
-    int f;
-  };
-};
-
-template <> struct A<bool> {
   struct B {
-    int g;
+    T f;
   };
 };

test/Import/template/test.cpp

 // RUN: clang-import-test -import %S/Inputs/T.cpp -expression %s
-// XFAIL: *
 void expr() {
-  A<int>::B b1;
-  A<bool>::B b2;
-  b1.f + b2.g;
+  A<int>::B b;
 }

tools/clang-import-test/clang-import-test.cpp

static llvm::cl::opt<std::string> Expression(
     llvm::cl::desc("Path to a file containing the expression to parse"));
 
 static llvm::cl::list<std::string>
     Imports("import", llvm::cl::ZeroOrMore,
             llvm::cl::desc("Path to a file containing declarations to import"));
 
 static llvm::cl::opt<bool>
     Direct("direct", llvm::cl::Optional,
-             llvm::cl::desc("Use the parsed declarations without indirection"));
 
+static llvm::cl::opt<bool>
+    UseOrigins("use-origins", llvm::cl::Optional,
+           llvm::cl::desc("Use DeclContext origin information for more accurate lookups"));  
+
 static llvm::cl::list<std::string>
     ClangArgs("Xcc", llvm::cl::ZeroOrMore,
               llvm::cl::desc("Argument to pass to the CompilerInvocation"),
               llvm::cl::CommaSeparated);
 
 static llvm::cl::opt<std::string>
     Input("x", llvm::cl::Optional,
           llvm::cl::desc("The language to parse (default: c++)"),
           llvm::cl::init("c++"));
 
-static llvm::cl::opt<bool>
-DumpAST("dump-ast", llvm::cl::init(false),
+static llvm::cl::opt<bool> DumpAST("dump-ast", llvm::cl::init(false),
                                    llvm::cl::desc("Dump combined AST"));
 
-static llvm::cl::opt<bool>
-DumpIR("dump-ir", llvm::cl::init(false),
+static llvm::cl::opt<bool> DumpIR("dump-ir", llvm::cl::init(false),
                                   llvm::cl::desc("Dump IR from final parse"));
 
 namespace init_convenience {
 class TestDiagnosticConsumer : public DiagnosticConsumer {
 private:
   std::unique_ptr<TextDiagnosticBuffer> Passthrough;
   const LangOptions *LangOpts = nullptr;
 
 public:
if (Info.hasSourceManager() && LangOpts) {
           llvm::errs() << Ref << '\n';
         }
       }
     }
     DiagnosticConsumer::HandleDiagnostic(DiagLevel, Info);
   }
 };
 
-std::unique_ptr<CompilerInstance>
-BuildCompilerInstance() {
+std::unique_ptr<CompilerInstance> BuildCompilerInstance() {
   auto Ins = llvm::make_unique<CompilerInstance>();
   auto DC = llvm::make_unique<TestDiagnosticConsumer>();
   const bool ShouldOwnClient = true;
   Ins->createDiagnostics(DC.release(), ShouldOwnClient);
 
   auto Inv = llvm::make_unique<CompilerInvocation>();
 
   std::vector<const char *> ClangArgv(ClangArgs.size());
std::unique_ptr<CodeGenerator> BuildCodeGen(CompilerInstance &CI,
   StringRef ModuleName("$__module");
   return std::unique_ptr<CodeGenerator>(CreateLLVMCodeGen(
       CI.getDiagnostics(), ModuleName, CI.getHeaderSearchOpts(),
       CI.getPreprocessorOpts(), CI.getCodeGenOpts(), LLVMCtx));
 }
 } // end namespace
 
 namespace {
- 
-void AddExternalSource(
-    CompilerInstance &CI,
-    llvm::ArrayRef<std::unique_ptr<CompilerInstance>> Imports) {
-  ExternalASTMerger::ImporterEndpoint Target({CI.getASTContext(), CI.getFileManager()});
-  llvm::SmallVector<ExternalASTMerger::ImporterEndpoint, 3> Sources;
-  for (const std::unique_ptr<CompilerInstance> &CI : Imports) {
-    Sources.push_back({CI->getASTContext(), CI->getFileManager()});
+struct CIAndOrigins {
+  using OriginMap = clang::ExternalASTMerger::OriginMap;
+  std::unique_ptr<CompilerInstance> CI;
+
+  ASTContext &getASTContext() { return CI->getASTContext(); }
+  FileManager &getFileManager() { return CI->getFileManager(); }
+  const OriginMap &getOriginMap() {
+    static const OriginMap EmptyOriginMap;
+    if (ExternalASTSource *Source = CI->getASTContext().getExternalSource())
+      return static_cast<ExternalASTMerger *>(Source)->GetOrigins();
+    else
+      return EmptyOriginMap;
+  }
+  DiagnosticConsumer &getDiagnosticClient() {
+    return CI->getDiagnosticClient();
+  }
+  CompilerInstance &getCompilerInstance() { return *CI; }
+};
+
+void AddExternalSource(CIAndOrigins &CI,
+                       llvm::MutableArrayRef<CIAndOrigins> Imports) {
+  ExternalASTMerger::ImporterTarget Target(
+      {CI.getASTContext(), CI.getFileManager()});
+  llvm::SmallVector<ExternalASTMerger::ImporterSource, 3> Sources;
+  for (CIAndOrigins &Import : Imports) {
+    Sources.push_back(
+        {Import.getASTContext(), Import.getFileManager(), Import.getOriginMap()});
   }
   auto ES = llvm::make_unique<ExternalASTMerger>(Target, Sources);
   CI.getASTContext().setExternalSource(ES.release());
   CI.getASTContext().getTranslationUnitDecl()->setHasExternalVisibleStorage();
 }
 
-std::unique_ptr<CompilerInstance> BuildIndirect(std::unique_ptr<CompilerInstance> &CI) {
-  std::unique_ptr<CompilerInstance> IndirectCI =
-      init_convenience::BuildCompilerInstance();
+CIAndOrigins BuildIndirect(CIAndOrigins &CI) {
+  CIAndOrigins IndirectCI{init_convenience::BuildCompilerInstance()};
   auto ST = llvm::make_unique<SelectorTable>();
   auto BC = llvm::make_unique<Builtin::Context>();
-  std::unique_ptr<ASTContext> AST =
-      init_convenience::BuildASTContext(*IndirectCI, *ST, *BC);
-  IndirectCI->setASTContext(AST.release());
-  AddExternalSource(*IndirectCI, CI);
+  std::unique_ptr<ASTContext> AST = init_convenience::BuildASTContext(
+      IndirectCI.getCompilerInstance(), *ST, *BC);
+  IndirectCI.getCompilerInstance().setASTContext(AST.release());
+  AddExternalSource(IndirectCI, CI);
   return IndirectCI;
 }
 
 llvm::Error ParseSource(const std::string &Path, CompilerInstance &CI,
                         ASTConsumer &Consumer) {
   SourceManager &SM = CI.getSourceManager();
   const FileEntry *FE = CI.getFileManager().getFile(Path);
   if (!FE) {
     return llvm::make_error<llvm::StringError>(
         llvm::Twine("Couldn't open ", Path), std::error_code());
   }
   SM.setMainFileID(SM.createFileID(FE, SourceLocation(), SrcMgr::C_User));
   ParseAST(CI.getPreprocessor(), &Consumer, CI.getASTContext());
   return llvm::Error::success();
 }
 
-llvm::Expected<std::unique_ptr<CompilerInstance>>
-Parse(const std::string &Path,
-      llvm::ArrayRef<std::unique_ptr<CompilerInstance>> Imports,
+llvm::Expected<CIAndOrigins> Parse(const std::string &Path,
+                                   llvm::MutableArrayRef<CIAndOrigins> Imports,
                                    bool ShouldDumpAST, bool ShouldDumpIR) {
-  std::unique_ptr<CompilerInstance> CI =
-      init_convenience::BuildCompilerInstance();
+  CIAndOrigins CI{init_convenience::BuildCompilerInstance()};
   auto ST = llvm::make_unique<SelectorTable>();
   auto BC = llvm::make_unique<Builtin::Context>();
   std::unique_ptr<ASTContext> AST =
-      init_convenience::BuildASTContext(*CI, *ST, *BC);
-  CI->setASTContext(AST.release());
+      init_convenience::BuildASTContext(CI.getCompilerInstance(), *ST, *BC);
+  CI.getCompilerInstance().setASTContext(AST.release());
   if (Imports.size())
-    AddExternalSource(*CI, Imports);
+    AddExternalSource(CI, Imports);
 
   std::vector<std::unique_ptr<ASTConsumer>> ASTConsumers;
 
   auto LLVMCtx = llvm::make_unique<llvm::LLVMContext>();
-  ASTConsumers.push_back(init_convenience::BuildCodeGen(*CI, *LLVMCtx));
-  auto &CG = *static_cast<CodeGenerator*>(ASTConsumers.back().get());
+  ASTConsumers.push_back(
+      init_convenience::BuildCodeGen(CI.getCompilerInstance(), *LLVMCtx));
+  auto &CG = *static_cast<CodeGenerator *>(ASTConsumers.back().get());
 
   if (ShouldDumpAST)
     ASTConsumers.push_back(CreateASTDumper("", true, false, false));
 
-  CI->getDiagnosticClient().BeginSourceFile(CI->getLangOpts(),
-                                            &CI->getPreprocessor());
+  CI.getDiagnosticClient().BeginSourceFile(
+      CI.getCompilerInstance().getLangOpts(),
+      &CI.getCompilerInstance().getPreprocessor());
   MultiplexConsumer Consumers(std::move(ASTConsumers));
-  Consumers.Initialize(CI->getASTContext());
+  Consumers.Initialize(CI.getASTContext());
 
-  if (llvm::Error PE = ParseSource(Path, *CI, Consumers)) {
+  if (llvm::Error PE = ParseSource(Path, CI.getCompilerInstance(), Consumers)) {
     return std::move(PE);
   }
-  CI->getDiagnosticClient().EndSourceFile();
+  CI.getDiagnosticClient().EndSourceFile();
   if (ShouldDumpIR)
     CG.GetModule()->print(llvm::outs(), nullptr);
-  if (CI->getDiagnosticClient().getNumErrors()) {
+  if (CI.getDiagnosticClient().getNumErrors()) {
     return llvm::make_error<llvm::StringError>(
         "Errors occured while parsing the expression.", std::error_code());
   } else {
     return std::move(CI);
   }
 }
 
+void Forget(CIAndOrigins &CI, llvm::MutableArrayRef<CIAndOrigins> Imports) {
+  llvm::SmallVector<ExternalASTMerger::ImporterSource, 3> Sources;
+  for (CIAndOrigins &Import : Imports) {
+    Sources.push_back(
+        {Import.getASTContext(), Import.getFileManager(), Import.getOriginMap()});
+  }
+  ExternalASTSource *Source = CI.CI->getASTContext().getExternalSource();
+  auto *Merger = static_cast<ExternalASTMerger *>(Source);
+  Merger->RemoveSources(Sources);
+}
+
 } // end namespace
 
 int main(int argc, const char **argv) {
   const bool DisableCrashReporting = true;
   llvm::sys::PrintStackTraceOnErrorSignal(argv[0], DisableCrashReporting);
   llvm::cl::ParseCommandLineOptions(argc, argv);
-  std::vector<std::unique_ptr<CompilerInstance>> ImportCIs;
+  std::vector<CIAndOrigins> ImportCIs;
   for (auto I : Imports) {
-    llvm::Expected<std::unique_ptr<CompilerInstance>> ImportCI =
-      Parse(I, {}, false, false);
+    llvm::Expected<CIAndOrigins> ImportCI = Parse(I, {}, false, false);
     if (auto E = ImportCI.takeError()) {
       llvm::errs() << llvm::toString(std::move(E));
       exit(-1);
     } else {
       ImportCIs.push_back(std::move(*ImportCI));
     }
   }
-  std::vector<std::unique_ptr<CompilerInstance>> IndirectCIs;
-  if (!Direct) {
+  std::vector<CIAndOrigins> IndirectCIs;
+  if (!Direct || UseOrigins) {
     for (auto &ImportCI : ImportCIs) {
-      std::unique_ptr<CompilerInstance> IndirectCI = BuildIndirect(ImportCI);
+      CIAndOrigins IndirectCI = BuildIndirect(ImportCI);
       IndirectCIs.push_back(std::move(IndirectCI));
     }
   }
-  llvm::Expected<std::unique_ptr<CompilerInstance>> ExpressionCI =
-      Parse(Expression, Direct ? ImportCIs : IndirectCIs, DumpAST, DumpIR);
+  if (UseOrigins) {
+    for (auto &ImportCI : ImportCIs) {
+      IndirectCIs.push_back(std::move(ImportCI));
+    }
+  }
+  llvm::Expected<CIAndOrigins> ExpressionCI =
+      Parse(Expression, (Direct && !UseOrigins) ? ImportCIs : IndirectCIs,
+            DumpAST, DumpIR);
   if (auto E = ExpressionCI.takeError()) {
     llvm::errs() << llvm::toString(std::move(E));
     exit(-1);
   } else {
+    Forget(*ExpressionCI, (Direct && !UseOrigins) ? ImportCIs : IndirectCIs);
     return 0;
   }
 }
-