Index: source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
+++ source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
@@ -186,7 +186,7 @@
 
   AccessType accessibility = eAccessNone;
   if (die) {
-    SymbolFileDWARF *dwarf = die.GetDWARF();
+    SymbolFileDWARF *dwarf = die.GetMainDWARF();
     if (log) {
       DWARFDIE context_die;
       clang::DeclContext *context =
@@ -3555,7 +3555,7 @@
 
 Type *DWARFASTParserClang::GetTypeForDIE(const DWARFDIE &die) {
   if (die) {
-    SymbolFileDWARF *dwarf = die.GetDWARF();
+    SymbolFileDWARF *dwarf = die.GetMainDWARF();
     DWARFAttributes attributes;
     const size_t num_attributes = die.GetAttributes(attributes);
     if (num_attributes > 0) {
@@ -3613,7 +3613,7 @@
   case DW_TAG_variable:
   case DW_TAG_constant:
   case DW_TAG_formal_parameter: {
-    SymbolFileDWARF *dwarf = die.GetDWARF();
+    SymbolFileDWARF *dwarf = die.GetMainDWARF();
     Type *type = GetTypeForDIE(die);
     if (dwarf && type) {
       const char *name = die.GetName();
@@ -3627,7 +3627,7 @@
     break;
   }
   case DW_TAG_imported_declaration: {
-    SymbolFileDWARF *dwarf = die.GetDWARF();
+    SymbolFileDWARF *dwarf = die.GetMainDWARF();
     DWARFDIE imported_uid = die.GetAttributeValueAsReferenceDIE(DW_AT_import);
     if (imported_uid) {
       CompilerDecl imported_decl = imported_uid.GetDecl();
@@ -3645,7 +3645,7 @@
     break;
   }
   case DW_TAG_imported_module: {
-    SymbolFileDWARF *dwarf = die.GetDWARF();
+    SymbolFileDWARF *dwarf = die.GetMainDWARF();
     DWARFDIE imported_uid = die.GetAttributeValueAsReferenceDIE(DW_AT_import);
 
     if (imported_uid) {
@@ -3701,7 +3701,7 @@
     }
 
     if (decl_ctx == nullptr && try_parsing_type) {
-      Type *type = die.GetDWARF()->ResolveType(die);
+      Type *type = die.GetMainDWARF()->ResolveType(die);
       if (type)
         decl_ctx = GetCachedClangDeclContextForDIE(die);
     }
Index: source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.h
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.h
+++ source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.h
@@ -213,6 +213,11 @@
 
   dw_offset_t GetBaseObjOffset() const { return m_data->m_base_obj_offset; }
 
+  // DW_TAG_compile_unit with DW_TAG_imported_unit for this DW_TAG_partial_unit.
+  DWARFCompileUnit *GetMainCU() const {
+    return const_cast<DWARFCompileUnit *>(this);
+  }
+
   dw_offset_t GetFileOffset() const { return m_data->m_file_offset; }
   dw_offset_t FileOffsetToUniqOffset(dw_offset_t file) const {
     return ThisCUFileOffsetToUniq(file);
Index: source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
+++ source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
@@ -600,7 +600,8 @@
       // Don't specify the compile unit offset as we don't know it because the
       // DIE belongs to
       // a different compile unit in the same symbol file.
-      return m_data->m_dwarf2Data->DebugInfo()->GetDIEForDIEOffset(die_offset);
+      return GetMainCU()->m_data->m_dwarf2Data->DebugInfo()
+          ->GetDIEForDIEOffset(die_offset);
     }
   }
   return DWARFDIE(); // Not found
@@ -1103,6 +1104,8 @@
 }
 
 LanguageType DWARFCompileUnit::GetLanguageType() {
+  if (GetMainCU() != this)
+    return GetMainCU()->GetLanguageType();
   if (m_data->m_language_type != eLanguageTypeUnknown)
     return m_data->m_language_type;
 
@@ -1140,6 +1143,8 @@
 }
 
 TypeSystem *DWARFCompileUnit::GetTypeSystem() {
+  if (GetMainCU() != this)
+    return GetMainCU()->GetTypeSystem();
   if (m_data->m_dwarf2Data)
     return m_data->m_dwarf2Data->GetTypeSystemForLanguage(GetLanguageType());
   else
Index: source/Plugins/SymbolFile/DWARF/DWARFDIE.h
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFDIE.h
+++ source/Plugins/SymbolFile/DWARF/DWARFDIE.h
@@ -57,6 +57,9 @@
   //----------------------------------------------------------------------
   SymbolFileDWARF *GetDWARF() const;
 
+  // File which referenced DWZCommonFile (where this DIE may be located).
+  SymbolFileDWARF *GetMainDWARF() const;
+
   DWARFCompileUnit *GetCU() const { return m_cu; }
 
   DWARFDebugInfoEntry *GetDIE() const { return m_die; }
Index: source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
+++ source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
@@ -135,7 +135,8 @@
     DWARFFormValue form_value;
     if (m_die->GetAttributeValue(dwarf, cu, attr, form_value, nullptr,
                                  check_specification_or_abstract_origin))
-      return dwarf->GetDIE(DIERef(form_value));
+      return cu->GetMainCU()->GetSymbolFileDWARF()
+          ->GetDIE(DIERef(form_value));
   }
   return DWARFDIE();
 }
@@ -241,7 +242,7 @@
 }
 
 lldb_private::Type *DWARFDIE::ResolveTypeUID(const DIERef &die_ref) const {
-  SymbolFileDWARF *dwarf = GetDWARF();
+  SymbolFileDWARF *dwarf = GetMainDWARF();
   if (dwarf)
     return dwarf->ResolveTypeUID(dwarf->GetDIE(die_ref), true);
   else
@@ -347,6 +348,13 @@
     return nullptr;
 }
 
+SymbolFileDWARF *DWARFDIE::GetMainDWARF() const {
+  if (m_cu)
+    return m_cu->GetMainCU()->GetSymbolFileDWARF();
+  else
+    return nullptr;
+}
+
 lldb_private::TypeSystem *DWARFDIE::GetTypeSystem() const {
   if (m_cu)
     return m_cu->GetTypeSystem();
Index: source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
+++ source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
@@ -76,6 +76,8 @@
     for (size_t idx = 0; idx < num_compile_units; ++idx) {
       DWARFCompileUnit *cu = GetCompileUnitAtIndex(idx);
 
+      if (cu->GetMainCU() != cu)
+        continue;
       dw_offset_t offset = cu->GetOffset();
       if (cus_with_data.find(offset) == cus_with_data.end()) {
         if (log) {
@@ -194,7 +196,10 @@
 }
 
 DWARFCompileUnit *DWARFDebugInfo::GetCompileUnit(const DIERef &die_ref) {
-  if (die_ref.cu_offset == DW_INVALID_OFFSET)
+  if (die_ref.cu_offset == DW_INVALID_OFFSET
+      // FIXME: Workaround default cu_offset = 0 in DIERef ctor.
+      // Why does GetCompileUnit exist at all?
+      || (die_ref.cu_offset == 0 /* && m_dwarf2Data->GetDWZSymbolFile() */ ))
     return GetCompileUnitContainingDIEOffset(die_ref.die_offset);
   else
     return GetCompileUnit(die_ref.cu_offset);
Index: source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp
+++ source/Plugins/SymbolFile/DWARF/DWARFDebugInfoEntry.cpp
@@ -385,6 +385,9 @@
     int &call_column, DWARFExpression *frame_base) const {
   if (dwarf2Data == nullptr)
     return false;
+  // DIERef(DWARFFormValue)->DWARFFormValue::Reference() may need
+  // FileOffsetToUniqOffset.
+  dwarf2Data->PreloadSymbols();
 
   SymbolFileDWARFDwo *dwo_symbol_file = cu->GetDwoSymbolFile();
   if (dwo_symbol_file)
@@ -569,7 +572,8 @@
   if (ranges.IsEmpty() || name == NULL || mangled == NULL) {
     for (const DIERef &die_ref : die_refs) {
       if (die_ref.die_offset != DW_INVALID_OFFSET) {
-        DWARFDIE die = dwarf2Data->GetDIE(die_ref);
+        DWARFDIE die = cu->GetMainCU()->GetSymbolFileDWARF()
+            ->GetDIE(die_ref);
         if (die)
           die.GetDIE()->GetDIENamesAndRanges(
               die.GetDWARF(), die.GetCU(), name, mangled, ranges, decl_file,
@@ -1323,7 +1327,7 @@
 void DWARFDebugInfoEntry::BuildAddressRangeTable(
     SymbolFileDWARF *dwarf2Data, const DWARFCompileUnit *cu,
     DWARFDebugAranges *debug_aranges) const {
-  if (m_tag) {
+  if (m_tag && m_tag != DW_TAG_partial_unit) {
     if (m_tag == DW_TAG_subprogram) {
       dw_addr_t lo_pc = LLDB_INVALID_ADDRESS;
       dw_addr_t hi_pc = LLDB_INVALID_ADDRESS;
Index: source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===================================================================
--- source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -735,6 +735,8 @@
 
     DWARFCompileUnit *dwarf_cu =
         info->GetCompileUnit((dw_offset_t)comp_unit->GetID());
+    if (dwarf_cu)
+      dwarf_cu = dwarf_cu->GetMainCU();
     if (dwarf_cu && dwarf_cu->GetUserData() == NULL)
       dwarf_cu->SetUserData(comp_unit);
     return dwarf_cu;
@@ -764,6 +766,7 @@
                                                    uint32_t cu_idx) {
   CompUnitSP cu_sp;
   if (dwarf_cu) {
+    dwarf_cu = dwarf_cu->GetMainCU();
     CompileUnit *comp_unit = (CompileUnit *)dwarf_cu->GetUserData();
     if (comp_unit) {
       // We already parsed this compile unit, had out a shared pointer to it
@@ -1371,6 +1374,9 @@
 
 Type *SymbolFileDWARF::ResolveTypeUID(const DWARFDIE &die,
                                       bool assert_not_being_parsed) {
+  // this can be neither die.GetDWARF() nor die.GetMainDWARF().
+  if (die.GetMainDWARF() != this)
+    return die.GetMainDWARF()->ResolveTypeUID(die, assert_not_being_parsed);
   if (die) {
     Log *log(LogChannelDWARF::GetLogIfAll(DWARF_LOG_DEBUG_INFO));
     if (log)
@@ -1483,6 +1489,10 @@
 Type *SymbolFileDWARF::ResolveType(const DWARFDIE &die,
                                    bool assert_not_being_parsed,
                                    bool resolve_function_context) {
+  // this can be neither die.GetDWARF() nor die.GetMainDWARF().
+  if (die.GetMainDWARF() != this)
+    return die.GetMainDWARF()->ResolveType(
+        die, assert_not_being_parsed, resolve_function_context);
   if (die) {
     Type *type = GetTypeForDIE(die, resolve_function_context).get();
 
@@ -1503,6 +1513,7 @@
 CompileUnit *
 SymbolFileDWARF::GetCompUnitForDWARFCompUnit(DWARFCompileUnit *dwarf_cu,
                                              uint32_t cu_idx) {
+  dwarf_cu = dwarf_cu->GetMainCU();
   // Check if the symbol vendor already knows about this compile unit?
   if (dwarf_cu->GetUserData() == NULL) {
     // The symbol vendor doesn't know about this compile unit, we