Index: llvm/include/llvm/Support/ConvertUTF.h
===================================================================
--- llvm/include/llvm/Support/ConvertUTF.h
+++ llvm/include/llvm/Support/ConvertUTF.h
@@ -243,6 +243,25 @@
 bool hasUTF16ByteOrderMark(ArrayRef<char> SrcBytes);
 
 /**
+ * Returns true if a blob of text starts with a UTF-8 byte order mark.
+ * UTF-8 BOM is a sequence of bytes on Windows and is not affected by the host
+ * system's endianness.
+ */
+bool hasUTF8ByteOrderMark(ArrayRef<char> SrcBytes);
+
+#ifdef LLVM_ON_WIN32
+/**
+ * Converts a stream of raw bytes assumed to be encoded in ANSI code page (aka
+ * Windows system locale) into a UTF8 std::string.
+ *
+ * \param [in] SrcBytes A buffer of what is assumed to be ANSI-encoded text.
+ * \param [out] Out Converted UTF-8 is stored here on success.
+ * \returns true on success
+ */
+bool convertANSIToUTF8String(ArrayRef<char> SrcBytes, std::string &Out);
+#endif
+
+/**
  * Converts a stream of raw bytes assumed to be UTF16 into a UTF8 std::string.
  *
  * \param [in] SrcBytes A buffer of what is assumed to be UTF-16 encoded text.
Index: llvm/lib/Support/CommandLine.cpp
===================================================================
--- llvm/lib/Support/CommandLine.cpp
+++ llvm/lib/Support/CommandLine.cpp
@@ -674,6 +674,20 @@
       return false;
     Str = StringRef(UTF8Buf);
   }
+  // If we see UTF-8 BOM sequence at the beginning of a file, we shall remove
+  // these bytes before parsing.
+  // Reference: http://en.wikipedia.org/wiki/UTF-8#Byte_order_mark
+  else if (hasUTF8ByteOrderMark(BufRef))
+    Str = StringRef(BufRef.data() + 3, BufRef.size() - 3);
+#ifdef LLVM_ON_WIN32
+  // Otherwise, this might be a hand-written text file encoded in the system's
+  // default code page.
+  else {
+    if (!convertANSIToUTF8String(BufRef, UTF8Buf))
+      return false;
+    Str = StringRef(UTF8Buf);
+  }
+#endif
 
   // Tokenize the contents into NewArgv.
   Tokenizer(Str, Saver, NewArgv, MarkEOLs);
Index: llvm/lib/Support/ConvertUTFWrapper.cpp
===================================================================
--- llvm/lib/Support/ConvertUTFWrapper.cpp
+++ llvm/lib/Support/ConvertUTFWrapper.cpp
@@ -12,6 +12,10 @@
 #include <string>
 #include <vector>
 
+#ifdef LLVM_ON_WIN32
+#include "Windows/WindowsSupport.h"
+#endif
+
 namespace llvm {
 
 bool ConvertUTF8toWide(unsigned WideCharWidth, llvm::StringRef Source,
@@ -81,6 +85,56 @@
            (S[0] == '\xfe' && S[1] == '\xff')));
 }
 
+// It is called byte order marker but the UTF-8 BOM is actually not affected
+// by the host system's endianness.
+bool hasUTF8ByteOrderMark(ArrayRef<char> S) {
+  return (S.size() >= 3 &&
+          S[0] == '\xef' && S[1] == '\xbb' && S[2] == '\xbf');
+}
+
+#ifdef LLVM_ON_WIN32
+// Convert system-locale encoded string to UTF8
+bool convertANSIToUTF8String(ArrayRef<char> SrcBytes, std::string &Out) {
+  assert(Out.empty());
+
+  if (SrcBytes.empty())
+    return true;
+
+  SmallVector<wchar_t, 128> utf16;
+  SmallVector<char, 128> utf8;
+
+  int len = ::MultiByteToWideChar(CP_ACP, MB_ERR_INVALID_CHARS, SrcBytes.data(),
+                                  SrcBytes.size(), utf16.begin(), 0);
+  if (len == 0)
+    return false;
+
+  utf16.reserve(len + 1);
+  utf16.set_size(len);
+
+  len = ::MultiByteToWideChar(CP_ACP, MB_ERR_INVALID_CHARS, SrcBytes.data(),
+                              SrcBytes.size(), utf16.begin(), utf16.size());
+  if (len == 0)
+    return false;
+
+  len = ::WideCharToMultiByte(CP_UTF8, 0, utf16.begin(), utf16.size(),
+                              utf8.begin(), 0, nullptr, nullptr);
+  if (len == 0)
+    return false;
+
+  utf8.reserve(len + 1);
+  utf8.set_size(len);
+
+  len = ::WideCharToMultiByte(CP_UTF8, 0, utf16.begin(), utf16.size(),
+                              utf8.data(), utf8.size(), nullptr, nullptr);
+  if (len == 0)
+    return false;
+
+  Out.resize(utf8.size());
+  std::copy(utf8.begin(), utf8.end(), Out.begin());
+  return true;
+}
+#endif // LLVM_ON_WIN32
+
 bool convertUTF16ToUTF8String(ArrayRef<char> SrcBytes, std::string &Out) {
   assert(Out.empty());