Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
@@ -319,6 +319,8 @@
 
   static lldb::LanguageType GetLanguage(DWARFUnit &unit);
 
+  typedef std::pair<int, std::string> FileSpecMapKey;
+  typedef std::map<FileSpecMapKey, lldb_private::FileSpec> FileSpecMap;
 protected:
   typedef llvm::DenseMap<const DWARFDebugInfoEntry *, lldb_private::Type *>
       DIEToTypePtr;
@@ -517,6 +519,7 @@
   llvm::DenseMap<dw_offset_t, lldb_private::FileSpecList>
       m_type_unit_support_files;
   std::vector<uint32_t> m_lldb_cu_to_dwarf_unit;
+  FileSpecMap m_file_spec_map;
 };
 
 #endif // LLDB_SOURCE_PLUGINS_SYMBOLFILE_DWARF_SYMBOLFILEDWARF_H
Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -224,6 +224,7 @@
 ParseSupportFilesFromPrologue(const lldb::ModuleSP &module,
                               const llvm::DWARFDebugLine::Prologue &prologue,
                               FileSpec::Style style,
+                              SymbolFileDWARF::FileSpecMap &file_spec_map,
                               llvm::StringRef compile_dir = {}) {
   FileSpecList support_files;
   size_t first_file = 0;
@@ -237,13 +238,29 @@
 
   const size_t number_of_files = prologue.FileNames.size();
   for (size_t idx = first_file; idx <= number_of_files; ++idx) {
-    std::string remapped_file;
-    if (auto file_path = GetFileByIndex(prologue, idx, compile_dir, style))
-      if (!module->RemapSourceFile(llvm::StringRef(*file_path), remapped_file))
-        remapped_file = std::move(*file_path);
+    FileSpec remapped_file;
+    // Constructing the paths and then validating when constructing the FileSpec has
+    // proven to be expensive in large C++ projects with lots of include files, so
+    // first we check if we've cached the FileSpec.
+    auto entry = prologue.getFileNameEntry(idx);
+    auto name = entry.Name.getAsCString();
+    if (name) {
+      SymbolFileDWARF::FileSpecMapKey key = {entry.DirIdx, *name};
+      auto map_entry = file_spec_map.find(key);
+      if (map_entry != file_spec_map.end()) {
+        remapped_file = map_entry->second;
+      } else if (auto file_path = GetFileByIndex(prologue, idx, compile_dir, style)) {
+        std::string remapped_file_name;
+        if (module->RemapSourceFile(llvm::StringRef(*file_path), remapped_file_name))
+          remapped_file = FileSpec(remapped_file_name, style);
+        else
+          remapped_file = FileSpec(std::move(*file_path), style);
+        file_spec_map.emplace(key, remapped_file);
+      }
+    }
 
     // Unconditionally add an entry, so the indices match up.
-    support_files.EmplaceBack(remapped_file, style);
+    support_files.EmplaceBack(remapped_file);
   }
 
   return support_files;
@@ -895,7 +912,7 @@
     return false;
 
   comp_unit.SetSupportFiles(ParseSupportFilesFromPrologue(
-      comp_unit.GetModule(), prologue, dwarf_cu->GetPathStyle(),
+      comp_unit.GetModule(), prologue, dwarf_cu->GetPathStyle(), m_file_spec_map,
       dwarf_cu->GetCompilationDirectory().GetCString()));
 
   return true;
@@ -942,7 +959,7 @@
       report(std::move(error));
     } else {
       list = ParseSupportFilesFromPrologue(GetObjectFile()->GetModule(),
-                                           prologue, tu.GetPathStyle());
+                                           prologue, tu.GetPathStyle(), m_file_spec_map);
     }
   }
   return list;