[modules] Defer merging deduced return types.

We can't read a deduced return type until we are sure that the types referred
to by it are not in the middle of being loaded. So defer all reading of such
deduced return types until the end of the recursive deserialization step.

Also, when we load a function type that has a deduced return type, update all
other redeclarations of the function to have that deduced return type.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@338798 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 78 insertions, 20 deletions

diff --git a/include/clang/Serialization/ASTReader.h b/include/clang/Serialization/ASTReader.h
index 0eecb6f5d6..b959f596f9 100644
--- a/include/clang/Serialization/ASTReader.h
+++ b/include/clang/Serialization/ASTReader.h
@@ -539,6 +539,11 @@ private:
   /// declaration that has an exception specification.
   llvm::SmallMapVector<Decl *, FunctionDecl *, 4> PendingExceptionSpecUpdates;
 
+  /// Deduced return type updates that have been loaded but not yet propagated
+  /// across the relevant redeclaration chain. The map key is the canonical
+  /// declaration and the value is the deduced return type.
+  llvm::SmallMapVector<FunctionDecl *, QualType, 4> PendingDeducedTypeUpdates;
+
   /// Declarations that have been imported and have typedef names for
   /// linkage purposes.
   llvm::DenseMap<std::pair<DeclContext *, IdentifierInfo *>, NamedDecl *>
@@ -1056,6 +1061,12 @@ private:
   /// Objective-C protocols.
   std::deque<InterestingDecl> PotentiallyInterestingDecls;
 
+  /// The list of deduced function types that we have not yet read, because
+  /// they might contain a deduced return type that refers to a local type
+  /// declared within the function.
+  SmallVector<std::pair<FunctionDecl *, serialization::TypeID>, 16>
+      PendingFunctionTypes;
+
   /// The list of redeclaration chains that still need to be
   /// reconstructed, and the local offset to the corresponding list
   /// of redeclarations.
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 723839ff62..8a02ea93f4 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -9254,7 +9254,7 @@ std::string ASTReader::getOwningModuleNameForDiagnostic(const Decl *D) {
 }
 
 void ASTReader::finishPendingActions() {
-  while (!PendingIdentifierInfos.empty() ||
+  while (!PendingIdentifierInfos.empty() || !PendingFunctionTypes.empty() ||
          !PendingIncompleteDeclChains.empty() || !PendingDeclChains.empty() ||
          !PendingMacroIDs.empty() || !PendingDeclContextInfos.empty() ||
          !PendingUpdateRecords.empty()) {
@@ -9273,6 +9273,21 @@ void ASTReader::finishPendingActions() {
       SetGloballyVisibleDecls(II, DeclIDs, &TopLevelDecls[II]);
     }
 
+    // Load each function type that we deferred loading because it was a
+    // deduced type that might refer to a local type declared within itself.
+    for (unsigned I = 0; I != PendingFunctionTypes.size(); ++I) {
+      auto *FD = PendingFunctionTypes[I].first;
+      FD->setType(GetType(PendingFunctionTypes[I].second));
+
+      // If we gave a function a deduced return type, remember that we need to
+      // propagate that along the redeclaration chain.
+      auto *DT = FD->getReturnType()->getContainedDeducedType();
+      if (DT && DT->isDeduced())
+        PendingDeducedTypeUpdates.insert(
+            {FD->getCanonicalDecl(), FD->getReturnType()});
+    }
+    PendingFunctionTypes.clear();
+
     // For each decl chain that we wanted to complete while deserializing, mark
     // it as "still needs to be completed".
     for (unsigned I = 0; I != PendingIncompleteDeclChains.size(); ++I) {
@@ -9282,7 +9297,8 @@ void ASTReader::finishPendingActions() {
 
     // Load pending declaration chains.
     for (unsigned I = 0; I != PendingDeclChains.size(); ++I)
-      loadPendingDeclChain(PendingDeclChains[I].first, PendingDeclChains[I].second);
+      loadPendingDeclChain(PendingDeclChains[I].first,
+                           PendingDeclChains[I].second);
     PendingDeclChains.clear();
 
     // Make the most recent of the top-level declarations visible.
@@ -11531,11 +11547,16 @@ void ASTReader::FinishedDeserializing() {
   --NumCurrentElementsDeserializing;
 
   if (NumCurrentElementsDeserializing == 0) {
-    // Propagate exception specification updates along redeclaration chains.
-    while (!PendingExceptionSpecUpdates.empty()) {
-      auto Updates = std::move(PendingExceptionSpecUpdates);
+    // Propagate exception specification and deduced type updates along
+    // redeclaration chains.
+    //
+    // We do this now rather than in finishPendingActions because we want to
+    // be able to walk the complete redeclaration chains of the updated decls.
+    while (!PendingExceptionSpecUpdates.empty() ||
+           !PendingDeducedTypeUpdates.empty()) {
+      auto ESUpdates = std::move(PendingExceptionSpecUpdates);
       PendingExceptionSpecUpdates.clear();
-      for (auto Update : Updates) {
+      for (auto Update : ESUpdates) {
         ProcessingUpdatesRAIIObj ProcessingUpdates(*this);
         auto *FPT = Update.second->getType()->castAs<FunctionProtoType>();
         auto ESI = FPT->getExtProtoInfo().ExceptionSpec;
@@ -11544,6 +11565,15 @@ void ASTReader::FinishedDeserializing() {
         for (auto *Redecl : Update.second->redecls())
           getContext().adjustExceptionSpec(cast<FunctionDecl>(Redecl), ESI);
       }
+
+      auto DTUpdates = std::move(PendingDeducedTypeUpdates);
+      PendingDeducedTypeUpdates.clear();
+      for (auto Update : DTUpdates) {
+        ProcessingUpdatesRAIIObj ProcessingUpdates(*this);
+        // FIXME: If the return type is already deduced, check that it matches.
+        getContext().adjustDeducedFunctionResultType(Update.first,
+                                                     Update.second);
+      }
     }
 
     if (ReadTimer)
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index d17ec8e046..613579d907 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -541,9 +541,6 @@ void ASTDeclReader::Visit(Decl *D) {
     // if we have a fully initialized TypeDecl, we can safely read its type now.
     ID->TypeForDecl = Reader.GetType(DeferredTypeID).getTypePtrOrNull();
   } else if (auto *FD = dyn_cast<FunctionDecl>(D)) {
-    if (DeferredTypeID)
-      FD->setType(Reader.GetType(DeferredTypeID));
-
     // FunctionDecl's body was written last after all other Stmts/Exprs.
     // We only read it if FD doesn't already have a body (e.g., from another
     // module).
@@ -844,10 +841,11 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
     // We'll set up the real type in Visit, once we've finished loading the
     // function.
     FD->setType(FD->getTypeSourceInfo()->getType());
+    Reader.PendingFunctionTypes.push_back({FD, DeferredTypeID});
   } else {
     FD->setType(Reader.GetType(DeferredTypeID));
-    DeferredTypeID = 0;
   }
+  DeferredTypeID = 0;
 
   ReadDeclarationNameLoc(FD->DNLoc, FD->getDeclName());
   FD->IdentifierNamespace = Record.readInt();
@@ -3370,6 +3368,11 @@ void ASTDeclReader::attachPreviousDeclImpl(ASTReader &Reader,
   }
 }
 
+static bool isUndeducedReturnType(QualType T) {
+  auto *DT = T->getContainedDeducedType();
+  return DT && !DT->isDeduced();
+}
+
 template<>
 void ASTDeclReader::attachPreviousDeclImpl(ASTReader &Reader,
                                            Redeclarable<FunctionDecl> *D,
@@ -3401,17 +3404,26 @@ void ASTDeclReader::attachPreviousDeclImpl(ASTReader &Reader,
     FD->setImplicitlyInline(true);
   }
 
-  // If we need to propagate an exception specification along the redecl
-  // chain, make a note of that so that we can do so later.
   auto *FPT = FD->getType()->getAs<FunctionProtoType>();
   auto *PrevFPT = PrevFD->getType()->getAs<FunctionProtoType>();
   if (FPT && PrevFPT) {
+    // If we need to propagate an exception specification along the redecl
+    // chain, make a note of that so that we can do so later.
     bool IsUnresolved = isUnresolvedExceptionSpec(FPT->getExceptionSpecType());
     bool WasUnresolved =
         isUnresolvedExceptionSpec(PrevFPT->getExceptionSpecType());
     if (IsUnresolved != WasUnresolved)
       Reader.PendingExceptionSpecUpdates.insert(
-          std::make_pair(Canon, IsUnresolved ? PrevFD : FD));
+          {Canon, IsUnresolved ? PrevFD : FD});
+
+    // If we need to propagate a deduced return type along the redecl chain,
+    // make a note of that so that we can do it later.
+    bool IsUndeduced = isUndeducedReturnType(FPT->getReturnType());
+    bool WasUndeduced = isUndeducedReturnType(PrevFPT->getReturnType());
+    if (IsUndeduced != WasUndeduced)
+      Reader.PendingDeducedTypeUpdates.insert(
+          {cast<FunctionDecl>(Canon),
+           (IsUndeduced ? PrevFPT : FPT)->getReturnType()});
   }
 }
 
@@ -4328,14 +4340,10 @@ void ASTDeclReader::UpdateDecl(Decl *D,
     }
 
     case UPD_CXX_DEDUCED_RETURN_TYPE: {
-      // FIXME: Also do this when merging redecls.
+      auto *FD = cast<FunctionDecl>(D);
       QualType DeducedResultType = Record.readType();
-      for (auto *Redecl : merged_redecls(D)) {
-        // FIXME: If the return type is already deduced, check that it matches.
-        auto *FD = cast<FunctionDecl>(Redecl);
-        Reader.getContext().adjustDeducedFunctionResultType(FD,
-                                                            DeducedResultType);
-      }
+      Reader.PendingDeducedTypeUpdates.insert(
+          {FD->getCanonicalDecl(), DeducedResultType});
       break;
     }
 
diff --git a/test/Modules/merge-deduced-return.cpp b/test/Modules/merge-deduced-return.cpp
index 0a4de7b975..71dc29b633 100644
--- a/test/Modules/merge-deduced-return.cpp
+++ b/test/Modules/merge-deduced-return.cpp
@@ -8,6 +8,8 @@ module A {}
 #pragma clang module begin A
 inline auto f() { struct X {}; return X(); }
 inline auto a = f();
+auto g(int);
+template<typename T> auto h(T t) { return g(t); }
 #pragma clang module end
 #pragma clang module endbuild
 
@@ -17,12 +19,14 @@ module B {}
 #pragma clang module begin B
 inline auto f() { struct X {}; return X(); }
 inline auto b = f();
+auto g(int) { return 0; }
 #pragma clang module end
 #pragma clang module endbuild
 
 #ifdef LOCAL
 inline auto f() { struct X {}; return X(); }
 inline auto b = f();
+auto g(int) { return 0; }
 #else
 #pragma clang module import B
 #endif
@@ -31,3 +35,5 @@ inline auto b = f();
 
 using T = decltype(a);
 using T = decltype(b);
+
+int test_g = h(0);
diff --git a/test/Modules/merge-lambdas.cpp b/test/Modules/merge-lambdas.cpp
index 8b3b501328..463a4c9b2f 100644
--- a/test/Modules/merge-lambdas.cpp
+++ b/test/Modules/merge-lambdas.cpp
@@ -46,3 +46,6 @@ using U = decltype(y2);
 
 using V = decltype(x3);
 using V = decltype(y3);
+
+#pragma clang module import A
+void (*p)() = f<int>();