Index: include/llvm/Support/SourceMgr.h
===================================================================
--- include/llvm/Support/SourceMgr.h
+++ include/llvm/Support/SourceMgr.h
@@ -138,6 +138,9 @@
   /// 0 is returned if the buffer is not found.
   unsigned FindBufferContainingLoc(SMLoc Loc) const;
 
+  /// Find the location for the Hash line in the buffer preceeding Loc
+  SMLoc FindCppHashLoc(SMLoc Loc, unsigned BufferID) const;
+  
   /// Find the line number for the specified location in the specified file.
   /// This is not a fast method.
   unsigned FindLineNumber(SMLoc Loc, unsigned BufferID = 0) const {
Index: lib/MC/MCParser/AsmParser.cpp
===================================================================
--- lib/MC/MCParser/AsmParser.cpp
+++ lib/MC/MCParser/AsmParser.cpp
@@ -207,6 +207,9 @@
   /// \brief Are we parsing ms-style inline assembly?
   bool ParsingInlineAsm;
 
+  /// \brief have we finished parsing the file?
+  bool FinishedParsing;
+  
 public:
   AsmParser(SourceMgr &SM, MCContext &Ctx, MCStreamer &Out,
             const MCAsmInfo &MAI);
@@ -576,7 +579,7 @@
     : Lexer(MAI), Ctx(Ctx), Out(Out), MAI(MAI), SrcMgr(SM),
       PlatformParser(nullptr), CurBuffer(SM.getMainFileID()),
       MacrosEnabledFlag(true), CppHashInfo(), AssemblerDialect(~0U),
-      IsDarwin(false), ParsingInlineAsm(false) {
+      IsDarwin(false), ParsingInlineAsm(false), FinishedParsing(false) {
   HadError = false;
   // Save the old handler.
   SavedDiagHandler = SrcMgr.getDiagHandler();
@@ -822,6 +825,9 @@
     }
   }
 
+  // Mark this run as finished
+  FinishedParsing = true;
+  
   // Finalize the output stream if there are no errors and if the client wants
   // us to.
   if (!HadError && !NoFinalize)
@@ -2144,11 +2150,38 @@
   const std::string &Filename = Parser->CppHashInfo.Filename;
 
   int DiagLocLineNo = DiagSrcMgr.FindLineNumber(DiagLoc, DiagBuf);
+  
+  // If we finished parsing CppHashLoc is invalid, so we need to recompute it
+  // from DiagBuf and DiagLoc.
+  SMLoc CppHashLoc;
+  int CppHashLineNumber;
+  if (Parser->FinishedParsing) {
+    CppHashLoc = Parser->SrcMgr.FindCppHashLoc(DiagLoc, DiagBuf);
+    
+    // From CppHashLoc, find line number (that's the number following the '#'
+    const char *Ptr = CppHashLoc.getPointer();
+    const char *Start = ++Ptr;
+    for (Ptr = Start; *Start == ' '; Start++, Ptr++);
+    for (; *Ptr != ' '; Ptr++);
+    
+    // Start points to the beginning of the number and Ptr to the end
+    StringRef LineNoStr(Start, Ptr - Start);
+    bool failed = LineNoStr.getAsInteger(0, CppHashLineNumber);
+    assert (!failed);
+  }
+  else {
+    CppHashLoc = Parser->CppHashInfo.Loc;
+    CppHashLineNumber = Parser->CppHashInfo.LineNumber;
+  }
+ 
   int CppHashLocLineNo =
-      Parser->SrcMgr.FindLineNumber(Parser->CppHashInfo.Loc, CppHashBuf);
+      Parser->SrcMgr.FindLineNumber(CppHashLoc, CppHashBuf);
   int LineNo =
-      Parser->CppHashInfo.LineNumber - 1 + (DiagLocLineNo - CppHashLocLineNo);
+      CppHashLineNumber - 1 + (DiagLocLineNo - CppHashLocLineNo);
 
+  // Better to crash than to be silly and report negative line number
+  assert (LineNo > 0);
+  
   SMDiagnostic NewDiag(*Diag.getSourceMgr(), Diag.getLoc(), Filename, LineNo,
                        Diag.getColumnNo(), Diag.getKind(), Diag.getMessage(),
                        Diag.getLineContents(), Diag.getRanges());
Index: lib/Support/SourceMgr.cpp
===================================================================
--- lib/Support/SourceMgr.cpp
+++ lib/Support/SourceMgr.cpp
@@ -74,6 +74,27 @@
   return 0;
 }
 
+SMLoc
+SourceMgr::FindCppHashLoc(SMLoc Loc, unsigned BufferID) const {
+  unsigned CppHashBuf = FindBufferContainingLoc(Loc);
+
+  // Initial implementation searches only for the previous '#' character
+  // after a newline: '\n[ ]*#'
+  const MemoryBuffer *Buff = getMemoryBuffer(BufferID);
+  const char *BufStart = Buff->getBufferStart();
+  const char *Ptr = BufStart;
+
+  SMLoc CppHashLoc;
+  
+  for (; SMLoc::getFromPointer(Ptr) != Loc; ++Ptr)
+    if (*Ptr == '#')
+      CppHashLoc = SMLoc::getFromPointer(Ptr);
+
+  assert(CppHashLoc.isValid());
+
+  return CppHashLoc;
+}
+
 std::pair<unsigned, unsigned>
 SourceMgr::getLineAndColumn(SMLoc Loc, unsigned BufferID) const {
   if (!BufferID)