Teach ModuleManager::addModule() to check whether a particular module

has already been loaded before allocating a new Module structure. If
the module has already been loaded (uniquing based on file name), then
just return the existing module rather than trying to load it again.

This allows us to load a DAG of modules. Introduce a simple test case
that forms a diamond-shaped module graph, and illustrates that a
source file importing the bottom of the diamond can see declarations
in all four of the modules that make up the diamond.

llvm-svn: 137925

clang/include/clang/Serialization/ASTReader.h

@@ -507,8 +507,11 @@ public:
   ///
   /// \param ImportedBy The module that is importing this module, or NULL if
   /// this module is imported directly by the user.
-  Module &addModule(StringRef FileName, ModuleKind Type,
-                    Module *ImportedBy);
+  ///
+  /// \return A pointer to the module that corresponds to this file name,
+  /// and a boolean indicating whether the module was newly added.
+  std::pair<Module *, bool> 
+  addModule(StringRef FileName, ModuleKind Type, Module *ImportedBy);
   
   /// \brief Add an in-memory buffer the list of known buffers
   void addInMemoryBuffer(StringRef FileName, llvm::MemoryBuffer *Buffer);

clang/lib/Serialization/ASTReader.cpp

@@ -2831,7 +2831,23 @@ ASTReader::ASTReadResult ASTReader::ReadAST(const std::string &FileName,
 ASTReader::ASTReadResult ASTReader::ReadASTCore(StringRef FileName,
                                                 ModuleKind Type,
                                                 Module *ImportedBy) {
-  Module &F = ModuleMgr.addModule(FileName, Type, ImportedBy);
+  Module *M;
+  bool NewModule;
+  llvm::tie(M, NewModule) = ModuleMgr.addModule(FileName, Type, ImportedBy);
+
+  if (!M) {
+    // We couldn't load the module.
+    std::string Msg = "Unable to load module \"" + FileName.str() + "\"";
+    Error(Msg);
+    return Failure;
+  }
+
+  if (!NewModule) {
+    // We've already loaded this module.
+    return Success;
+  }
+
+  Module &F = *M;
 
   if (FileName != "-") {
     CurrentDir = llvm::sys::path::parent_path(FileName);
@@ -5709,25 +5725,34 @@ llvm::MemoryBuffer *ModuleManager::lookupBuffer(StringRef Name) {
   return InMemoryBuffers[Entry];
 }
 
-/// \brief Creates a new module and adds it to the list of known modules
-Module &ModuleManager::addModule(StringRef FileName, ModuleKind Type,
-                                 Module *ImportedBy) {
-  Module *Current = new Module(Type);
-  Current->FileName = FileName.str();
-  Chain.push_back(Current);
-
+std::pair<Module *, bool>
+ModuleManager::addModule(StringRef FileName, ModuleKind Type, 
+                         Module *ImportedBy) {
   const FileEntry *Entry = FileMgr.getFile(FileName);
-  // FIXME: Check whether we already loaded this module, before 
-  Modules[Entry] = Current;
+  if (!Entry)
+    return std::make_pair(static_cast<Module*>(0), false);
 
-  if (ImportedBy) {
-    Current->ImportedBy.insert(ImportedBy);
-    ImportedBy->Imports.insert(Current);
-  } else {
-    Current->DirectlyImported = true;
+  // Check whether we already loaded this module, before 
+  Module *&ModuleEntry = Modules[Entry];
+  bool NewModule = false;
+  if (!ModuleEntry) {
+    // Allocate a new module.
+    Module *New = new Module(Type);
+    New->FileName = FileName.str();
+    Chain.push_back(New);
+  
+    NewModule = true;
+    ModuleEntry = New;
   }
 
-  return *Current;
+  if (ImportedBy) {
+    ModuleEntry->ImportedBy.insert(ImportedBy);
+    ImportedBy->Imports.insert(ModuleEntry);
+  } else {
+    ModuleEntry->DirectlyImported = true;
+  }
+  
+  return std::make_pair(ModuleEntry, NewModule);
 }
 
 void ModuleManager::addInMemoryBuffer(StringRef FileName, 

clang/test/Modules/Inputs/diamond_bottom.h

@@ -0,0 +1 @@
+char bottom(char *x);

clang/test/Modules/Inputs/diamond_left.h

@@ -0,0 +1 @@
+float left(float *);

clang/test/Modules/Inputs/diamond_right.h

@@ -0,0 +1 @@
+double right(double *);

clang/test/Modules/Inputs/diamond_top.h

@@ -0,0 +1 @@
+int top(int *);

clang/test/Modules/diamond.c

@@ -0,0 +1,14 @@
+// in diamond-bottom.h: expected-note{{passing argument to parameter 'x' here}}
+void test_diamond(int i, float f, double d, char c) {
+  top(&i);
+  left(&f);
+  right(&d);
+  bottom(&c);
+  bottom(&d); // expected-warning{{incompatible pointer types passing 'double *' to parameter of type 'char *'}}
+}
+
+// RUN: %clang_cc1 -emit-pch -o %t_top.h.pch %S/Inputs/diamond_top.h
+// RUN: %clang_cc1 -import-module %t_top.h.pch -emit-pch -o %t_left.h.pch %S/Inputs/diamond_left.h
+// RUN: %clang_cc1 -import-module %t_top.h.pch -emit-pch -o %t_right.h.pch %S/Inputs/diamond_right.h
+// RUN: %clang_cc1 -import-module %t_left.h.pch -import-module %t_right.h.pch -emit-pch -o %t_bottom.h.pch %S/Inputs/diamond_bottom.h
+// RUN: %clang_cc1 -import-module %t_bottom.h.pch -verify %s