Index: lib/Basic/SourceManager.cpp
===================================================================
--- lib/Basic/SourceManager.cpp
+++ lib/Basic/SourceManager.cpp
@@ -1144,8 +1144,18 @@
     unsigned *SourceLineCache = LastLineNoContentCache->SourceLineCache;
     unsigned LineStart = SourceLineCache[LastLineNoResult - 1];
     unsigned LineEnd = SourceLineCache[LastLineNoResult];
-    if (FilePos >= LineStart && FilePos < LineEnd)
+    if (FilePos >= LineStart && FilePos < LineEnd) {
+      // LineEnd is the LineStart of the next line.
+      // A line ends with separator LF or CR+LF on Windows.
+      // FilePos might point to the last separator,
+      // but we need a column number at most 1 + the last column.
+      if (FilePos + 1 == LineEnd && FilePos > LineStart) {
+        const char *Buf = MemBuf->getBufferStart();
+        if (Buf[FilePos - 1] == '\r' || Buf[FilePos - 1] == '\n')
+          --FilePos;
+      }
       return FilePos - LineStart + 1;
+    }
   }
 
   const char *Buf = MemBuf->getBufferStart();