Index: lib/DebugInfo/DWARF/DWARFDebugLine.cpp
===================================================================
--- lib/DebugInfo/DWARF/DWARFDebugLine.cpp
+++ lib/DebugInfo/DWARF/DWARFDebugLine.cpp
@@ -953,6 +953,14 @@
   return None;
 }
 
+static bool isPathAbsoluteOnWindowsOrPosix(const Twine &Path) {
+  // Debug info can contain paths from any OS, not necessarily
+  // an OS we're currently running on. Moreover different compilation units can
+  // be compiled on different operating systems and linked together later.
+  return sys::path::is_absolute(Path, sys::path::Style::posix) ||
+         sys::path::is_absolute(Path, sys::path::Style::windows);
+}
+
 bool DWARFDebugLine::LineTable::getFileNameByIndex(uint64_t FileIndex,
                                                    const char *CompDir,
                                                    FileLineInfoKind Kind,
@@ -962,7 +970,7 @@
   const FileNameEntry &Entry = Prologue.FileNames[FileIndex - 1];
   StringRef FileName = Entry.Name.getAsCString().getValue();
   if (Kind != FileLineInfoKind::AbsoluteFilePath ||
-      sys::path::is_absolute(FileName)) {
+      isPathAbsoluteOnWindowsOrPosix(FileName)) {
     Result = FileName;
     return true;
   }
@@ -981,7 +989,7 @@
   // We know that FileName is not absolute, the only way to have an
   // absolute path at this point would be if IncludeDir is absolute.
   if (CompDir && Kind == FileLineInfoKind::AbsoluteFilePath &&
-      sys::path::is_relative(IncludeDir))
+      !isPathAbsoluteOnWindowsOrPosix(IncludeDir))
     sys::path::append(FilePath, CompDir);
 
   // sys::path::append skips empty strings.