Index: llvm/trunk/lib/MC/MCParser/AsmParser.cpp
===================================================================
--- llvm/trunk/lib/MC/MCParser/AsmParser.cpp
+++ llvm/trunk/lib/MC/MCParser/AsmParser.cpp
@@ -165,6 +165,9 @@
   };
   CppHashInfoTy CppHashInfo;
 
+  /// The filename from the first cpp hash file line comment, if any.
+  StringRef FirstCppHashFilename;
+
   /// List of forward directional labels for diagnosis at the end.
   SmallVector<std::tuple<SMLoc, CppHashInfoTy, MCSymbol *>, 4> DirLabels;
 
@@ -849,6 +852,13 @@
   // the assembler source was produced with debug info already) then emit one
   // describing the assembler source file itself.
   if (getContext().getGenDwarfFileNumber() == 0) {
+    // Use the first #line directive for this, if any. It's preprocessed, so
+    // there is no checksum, and of course no source directive.
+    if (!FirstCppHashFilename.empty())
+      getContext().setMCLineTableRootFile(/*CUID=*/0,
+                                          getContext().getCompilationDir(),
+                                          FirstCppHashFilename,
+                                          /*Cksum=*/None, /*Source=*/None);
     const MCDwarfFile &RootFile =
         getContext().getMCDwarfLineTable(/*CUID=*/0).getRootFile();
     getContext().setGenDwarfFileNumber(getStreamer().EmitDwarfFileDirective(
@@ -2285,11 +2295,14 @@
   // Get rid of the enclosing quotes.
   Filename = Filename.substr(1, Filename.size() - 2);
 
-  // Save the SMLoc, Filename and LineNumber for later use by diagnostics.
+  // Save the SMLoc, Filename and LineNumber for later use by diagnostics
+  // and possibly DWARF file info.
   CppHashInfo.Loc = L;
   CppHashInfo.Filename = Filename;
   CppHashInfo.LineNumber = LineNumber;
   CppHashInfo.Buf = CurBuffer;
+  if (FirstCppHashFilename.empty())
+    FirstCppHashFilename = Filename;
   return false;
 }
 
Index: llvm/trunk/test/MC/ELF/debug-hash-file.s
===================================================================
--- llvm/trunk/test/MC/ELF/debug-hash-file.s
+++ llvm/trunk/test/MC/ELF/debug-hash-file.s
@@ -0,0 +1,21 @@
+// RUN: llvm-mc -triple x86_64-unknown-linux-gnu -filetype obj -g -dwarf-version 4 -o %t %s
+// RUN: llvm-dwarfdump -debug-info -debug-line %t | FileCheck %s
+
+// CHECK: DW_TAG_compile_unit
+// CHECK-NOT: DW_TAG_
+// CHECK: DW_AT_name      ("/MyTest/Inputs{{(/|\\)+}}other.S")
+// CHECK: DW_TAG_label
+// CHECK-NOT: DW_TAG_
+// CHECK: DW_AT_decl_file ("/MyTest/Inputs{{(/|\\)+}}other.S")
+
+// CHECK: include_directories[ 1] = "/MyTest/Inputs"
+// CHECK: file_names[ 1]:
+// CHECK-NEXT: name: "other.S"
+// CHECK-NEXT: dir_index: 1
+
+# 1 "/MyTest/Inputs/other.S"
+
+foo:
+  nop
+  nop
+  nop