Debug Info: Generate imported entities for implicitly imported parent modules.

The Swift compiler uses an ugly hack that auto-imports a submodule's
top-level-module, even if we didn't ask for it. Reflect that in the
debug info.

<rdar://problem/31310320>

Author: adrian-prantl

lib/IRGen/IRGenDebugInfo.cpp

@@ -96,6 +96,8 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
 
   /// A list of replaceable fwddecls that need to be RAUWed at the end.
   std::vector<std::pair<TypeBase *, llvm::TrackingMDRef>> ReplaceMap;
+  /// The set of imported modules.
+  llvm::DenseSet<ModuleDecl::ImportedModule> ImportedModules;
 
   llvm::BumpPtrAllocator DebugInfoNames;
   StringRef CWDName;                    /// The current working directory.
@@ -1550,6 +1552,15 @@ IRGenDebugInfoImpl::IRGenDebugInfoImpl(const IRGenOptions &Opts,
 void IRGenDebugInfoImpl::finalize() {
   assert(LocationStack.empty() && "Mismatch of pushLoc() and popLoc().");
 
+  // Get the list of imported modules (which may actually be different
+  // from all ImportDecls).
+  SmallVector<ModuleDecl::ImportedModule, 8> ModuleWideImports;
+  IGM.getSwiftModule()->getImportedModules(ModuleWideImports,
+                                           ModuleDecl::ImportFilter::All);
+  for (auto M : ModuleWideImports)
+    if (!ImportedModules.count(M))
+       DBuilder.createImportedModule(MainFile, getOrCreateModule(M), 0);
+
   // Finalize all replaceable forward declarations.
   for (auto &Ty : ReplaceMap) {
     llvm::TempMDNode FwdDecl(cast<llvm::MDNode>(Ty.second));
@@ -1716,9 +1727,11 @@ void IRGenDebugInfoImpl::emitImport(ImportDecl *D) {
     assert(M && "Could not find module for import decl.");
     return;
   }
-  auto DIMod = getOrCreateModule({D->getModulePath(), M});
+  ModuleDecl::ImportedModule Imported = {D->getModulePath(), M};
+  auto DIMod = getOrCreateModule(Imported);
   auto L = getDebugLoc(*this, D);
   DBuilder.createImportedModule(getOrCreateFile(L.Filename), DIMod, L.Line);
+  ImportedModules.insert(Imported);
 }
 
 llvm::DISubprogram *IRGenDebugInfoImpl::emitFunction(SILFunction &SILFn,

test/DebugInfo/ImportClangSubmodule.swift

@@ -10,7 +10,12 @@
 // CHECK-SAME:                         configMacros:
 // CHECK-SAME:                         {{..}}-DFOO=foo{{..}}
 // CHECK-SAME:                         {{..}}-UBAR{{..}}
+
 // CHECK: !DIImportedEntity({{.*}}, entity: ![[SUBMODULE]], line: [[@LINE+1]])
 import ClangModule.SubModule
 
+// The Swift compiler uses an ugly hack that auto-imports a
+// submodule's top-level-module, even if we didn't ask for it.
+// CHECK: !DIImportedEntity({{.*}}, entity: ![[CLANGMODULE]])
+
 let bar = Bar()