Index: COFF/PDB.cpp
===================================================================
--- COFF/PDB.cpp
+++ COFF/PDB.cpp
@@ -115,11 +115,11 @@
   /// If the object does not use a type server PDB (compiled with /Z7), we merge
   /// all the type and item records from the .debug$S stream and fill in the
   /// caller-provided ObjectIndexMap.
-  Expected<const CVIndexMap&> mergeDebugT(ObjFile *File,
-                                          CVIndexMap &ObjectIndexMap);
+  Expected<const CVIndexMap &> mergeDebugT(ObjFile *File,
+                                           CVIndexMap &ObjectIndexMap);
 
-  Expected<const CVIndexMap&> maybeMergeTypeServerPDB(ObjFile *File,
-                                                      TypeServer2Record &TS);
+  Expected<const CVIndexMap &> maybeMergeTypeServerPDB(ObjFile *File,
+                                                       TypeServer2Record &TS);
 
   /// Add the section map and section contributions to the PDB.
   void addSections(ArrayRef<OutputSection *> OutputSections,
@@ -256,8 +256,8 @@
   return std::move(TS);
 }
 
-Expected<const CVIndexMap&> PDBLinker::mergeDebugT(ObjFile *File,
-                                                   CVIndexMap &ObjectIndexMap) {
+Expected<const CVIndexMap &>
+PDBLinker::mergeDebugT(ObjFile *File, CVIndexMap &ObjectIndexMap) {
   ScopedTimer T(TypeMergingTimer);
 
   ArrayRef<uint8_t> Data = getDebugSection(File, ".debug$T");
@@ -332,15 +332,15 @@
   return std::move(NS);
 }
 
-Expected<const CVIndexMap&> PDBLinker::maybeMergeTypeServerPDB(ObjFile *File,
-                                                               TypeServer2Record &TS) {
-  const GUID& TSId = TS.getGuid();
+Expected<const CVIndexMap &>
+PDBLinker::maybeMergeTypeServerPDB(ObjFile *File, TypeServer2Record &TS) {
+  const GUID &TSId = TS.getGuid();
   StringRef TSPath = TS.getName();
 
   // First, check if the PDB has previously failed to load.
   if (MissingTypeServerPDBs.count(TSId))
     return make_error<pdb::GenericError>(
-      pdb::generic_error_code::type_server_not_found, TSPath);
+        pdb::generic_error_code::type_server_not_found, TSPath);
 
   // Second, check if we already loaded a PDB with this GUID. Return the type
   // index mapping if we have it.
@@ -361,8 +361,8 @@
     StringRef LocalPath =
         !File->ParentName.empty() ? File->ParentName : File->getName();
     SmallString<128> Path = sys::path::parent_path(LocalPath);
-    sys::path::append(
-        Path, sys::path::filename(TSPath, sys::path::Style::windows));
+    sys::path::append(Path,
+                      sys::path::filename(TSPath, sys::path::Style::windows));
     ExpectedSession = tryToLoadPDB(TSId, Path);
   }
   if (auto E = ExpectedSession.takeError()) {
@@ -1085,6 +1085,21 @@
       EBS, Allocator, CodeViewContainer::Pdb));
 }
 
+static void addLinkerModuleCoffGroup(const Chunk *firstChunk,
+                                     const Chunk *lastChunk,
+                                     pdb::DbiModuleDescriptorBuilder &Mod,
+                                     OutputSection &OS,
+                                     BumpPtrAllocator &Allocator) {
+  CoffGroupSym CGS(SymbolRecordKind::CoffGroupSym);
+  CGS.Name = firstChunk->getSectionName();
+  CGS.Segment = OS.SectionIndex;
+  CGS.Offset = firstChunk->getRVA() - OS.getRVA();
+  CGS.Size = lastChunk->getRVA() + lastChunk->getSize() - firstChunk->getRVA();
+  CGS.Characteristics = firstChunk->getOutputCharacteristics();
+  Mod.addSymbol(codeview::SymbolSerializer::writeOneSymbol(
+      CGS, Allocator, CodeViewContainer::Pdb));
+}
+
 static void addLinkerModuleSectionSymbol(pdb::DbiModuleDescriptorBuilder &Mod,
                                          OutputSection &OS,
                                          BumpPtrAllocator &Allocator) {
@@ -1097,6 +1112,39 @@
   Sym.SectionNumber = OS.SectionIndex;
   Mod.addSymbol(codeview::SymbolSerializer::writeOneSymbol(
       Sym, Allocator, CodeViewContainer::Pdb));
+
+  // Output COFF groups for individual chunks of this section.
+  // There may be several chunks with the same name (e.g. .text$di), but we only
+  // want to output each unique chunk once.
+  Chunk *firstChunkInSubSection = nullptr;
+  Chunk *lastChunkInSubSection = nullptr;
+
+  for (Chunk *C : OS.getChunks()) {
+    auto *SecChunk = dyn_cast<SectionChunk>(C);
+
+    // If this chunk doesn't represent an unmerged input file chunk, or it
+    // didn't contribute to the final output file, skip it.
+    if (!SecChunk || !SecChunk->isLive())
+      continue;
+
+    if (!firstChunkInSubSection) {
+      firstChunkInSubSection = C;
+    }
+
+    if (C->getSectionName() != firstChunkInSubSection->getSectionName()) {
+      addLinkerModuleCoffGroup(firstChunkInSubSection, lastChunkInSubSection,
+                               Mod, OS, Allocator);
+
+      firstChunkInSubSection = C;
+    }
+
+    lastChunkInSubSection = C;
+  }
+
+  if (firstChunkInSubSection && lastChunkInSubSection) {
+    addLinkerModuleCoffGroup(firstChunkInSubSection, lastChunkInSubSection, Mod,
+                             OS, Allocator);
+  }
 }
 
 // Creates a PDB file.