Index: include/llvm/DebugInfo/DWARF/DWARFDebugLine.h
===================================================================
--- include/llvm/DebugInfo/DWARF/DWARFDebugLine.h
+++ include/llvm/DebugInfo/DWARF/DWARFDebugLine.h
@@ -188,6 +188,9 @@
     bool lookupAddressRange(uint64_t address, uint64_t size,
                             std::vector<uint32_t> &result) const;
 
+    bool hasFileNameByIndex(uint64_t FileIndex,
+                            DILineInfoSpecifier::FileLineInfoKind Kind) const;
+
     // Extracts filename by its index in filename table in prologue.
     // Returns true on success.
     bool getFileNameByIndex(uint64_t FileIndex, const char *CompDir,
Index: lib/DebugInfo/DWARF/DWARFDebugLine.cpp
===================================================================
--- lib/DebugInfo/DWARF/DWARFDebugLine.cpp
+++ lib/DebugInfo/DWARF/DWARFDebugLine.cpp
@@ -624,13 +624,22 @@
   return true;
 }
 
-bool DWARFDebugLine::LineTable::getFileNameByIndex(uint64_t FileIndex,
-                                                   const char *CompDir,
-                                                   FileLineInfoKind Kind,
-                                                   std::string &Result) const {
+bool
+DWARFDebugLine::LineTable::hasFileNameByIndex(uint64_t FileIndex,
+                                              FileLineInfoKind Kind) const {
   if (FileIndex == 0 || FileIndex > Prologue.FileNames.size() ||
       Kind == FileLineInfoKind::None)
     return false;
+  return true;
+}
+
+bool
+DWARFDebugLine::LineTable::getFileNameByIndex(uint64_t FileIndex,
+                                              const char *CompDir,
+                                              FileLineInfoKind Kind,
+                                              std::string &Result) const {
+  if (!hasFileNameByIndex(FileIndex, Kind))
+    return false;
   const FileNameEntry &Entry = Prologue.FileNames[FileIndex - 1];
   const char *FileName = Entry.Name;
   if (Kind != FileLineInfoKind::AbsoluteFilePath ||
Index: tools/dsymutil/DwarfLinker.cpp
===================================================================
--- tools/dsymutil/DwarfLinker.cpp
+++ tools/dsymutil/DwarfLinker.cpp
@@ -1633,11 +1633,8 @@
           // FIXME: Passing U.getOrigUnit().getCompilationDir()
           // instead of "" would allow more uniquing, but for now, do
           // it this way to match dsymutil-classic.
-          std::string File;
-          if (LT->getFileNameByIndex(
-                  FileNum, "",
-                  DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath,
-                  File)) {
+          if (LT->hasFileNameByIndex(FileNum,
+                    DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath)) {
             Line = DIE->getAttributeValueAsUnsignedConstant(
                 &U.getOrigUnit(), dwarf::DW_AT_decl_line, 0);
             // Cache the resolved paths, because calling realpath is expansive.
@@ -1646,6 +1643,13 @@
               FileRef = ResolvedPath;
             } else {
 #ifdef HAVE_REALPATH
+              std::string File;
+              bool gotFileName =
+                LT->getFileNameByIndex(FileNum, "",
+                        DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath,
+                        File);
+              (void)gotFileName;
+              assert(gotFileName && "Must get file name from line table");
               char RealPath[PATH_MAX + 1];
               RealPath[PATH_MAX] = 0;
               if (::realpath(File.c_str(), RealPath))