[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.

llvm-svn: 338798

2 files changed, 58 insertions, 20 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 723839ff62b..8a02ea93f40 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/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/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index d17ec8e0461..613579d9079 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/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;
     }