Index: lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
===================================================================
--- lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
+++ lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
@@ -319,6 +319,9 @@
 
   static lldb::LanguageType GetLanguage(DWARFUnit &unit);
 
+  typedef std::pair<std::string, std::string> FileSpecMapKey;
+  typedef std::map<FileSpecMapKey, lldb_private::FileSpec> FileSpecMap;
+
 protected:
   typedef llvm::DenseMap<const DWARFDebugInfoEntry *, lldb_private::Type *>
       DIEToTypePtr;
@@ -517,6 +520,7 @@
   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 +238,32 @@
 
   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);
+    std::string includeDir;
+    includeDir += prologue.getIncludeDirectoryFromEntry(
+        entry, llvm::DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath);
+    SymbolFileDWARF::FileSpecMapKey key = {includeDir,
+                                           *(entry.Name.getAsCString())};
+    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;
@@ -896,7 +916,7 @@
 
   comp_unit.SetSupportFiles(ParseSupportFilesFromPrologue(
       comp_unit.GetModule(), prologue, dwarf_cu->GetPathStyle(),
-      dwarf_cu->GetCompilationDirectory().GetCString()));
+      m_file_spec_map, dwarf_cu->GetCompilationDirectory().GetCString()));
 
   return true;
 }
@@ -941,8 +961,9 @@
     if (error) {
       report(std::move(error));
     } else {
-      list = ParseSupportFilesFromPrologue(GetObjectFile()->GetModule(),
-                                           prologue, tu.GetPathStyle());
+      list =
+          ParseSupportFilesFromPrologue(GetObjectFile()->GetModule(), prologue,
+                                        tu.GetPathStyle(), m_file_spec_map);
     }
   }
   return list;
Index: llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h
===================================================================
--- llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h
+++ llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h
@@ -118,6 +118,9 @@
     /// index.
     const llvm::DWARFDebugLine::FileNameEntry &
     getFileNameEntry(uint64_t Index) const;
+    StringRef getIncludeDirectoryFromEntry(
+        const llvm::DWARFDebugLine::FileNameEntry &Entry,
+        DILineInfoSpecifier::FileLineInfoKind Kind) const;
 
     bool hasFileAtIndex(uint64_t FileIndex) const;
 
Index: llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
===================================================================
--- llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
+++ llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
@@ -1365,19 +1365,7 @@
   }
 
   SmallString<16> FilePath;
-  StringRef IncludeDir;
-  // Be defensive about the contents of Entry.
-  if (getVersion() >= 5) {
-    // DirIdx 0 is the compilation directory, so don't include it for
-    // relative names.
-    if ((Entry.DirIdx != 0 || Kind != FileLineInfoKind::RelativeFilePath) &&
-        Entry.DirIdx < IncludeDirectories.size())
-      IncludeDir = IncludeDirectories[Entry.DirIdx].getAsCString().getValue();
-  } else {
-    if (0 < Entry.DirIdx && Entry.DirIdx <= IncludeDirectories.size())
-      IncludeDir =
-          IncludeDirectories[Entry.DirIdx - 1].getAsCString().getValue();
-  }
+  StringRef IncludeDir = getIncludeDirectoryFromEntry(Entry, Kind);
 
   // For absolute paths only, include the compilation directory of compile unit.
   // We know that FileName is not absolute, the only way to have an absolute
@@ -1396,6 +1384,25 @@
   return true;
 }
 
+StringRef DWARFDebugLine::Prologue::getIncludeDirectoryFromEntry(
+    const llvm::DWARFDebugLine::FileNameEntry &Entry,
+    FileLineInfoKind Kind) const {
+  StringRef IncludeDir;
+  // Be defensive about the contents of Entry.
+  if (getVersion() >= 5) {
+    // DirIdx 0 is the compilation directory, so don't include it for
+    // relative names.
+    if ((Entry.DirIdx != 0 || Kind != FileLineInfoKind::RelativeFilePath) &&
+        Entry.DirIdx < IncludeDirectories.size())
+      IncludeDir = IncludeDirectories[Entry.DirIdx].getAsCString().getValue();
+  } else {
+    if (0 < Entry.DirIdx && Entry.DirIdx <= IncludeDirectories.size())
+      IncludeDir =
+          IncludeDirectories[Entry.DirIdx - 1].getAsCString().getValue();
+  }
+  return IncludeDir;
+}
+
 bool DWARFDebugLine::LineTable::getFileLineInfoForAddress(
     object::SectionedAddress Address, const char *CompDir,
     FileLineInfoKind Kind, DILineInfo &Result) const {