Index: llvm/trunk/tools/opt-viewer/opt-viewer.py
===================================================================
--- llvm/trunk/tools/opt-viewer/opt-viewer.py
+++ llvm/trunk/tools/opt-viewer/opt-viewer.py
@@ -10,6 +10,7 @@
 import os.path
 import re
 import shutil
+import sys
 
 from pygments import highlight
 from pygments.lexers.c_cpp import CppLexer
@@ -62,7 +63,11 @@
         html_highlighted = highlight(
             file_text,
             self.cpp_lexer,
-            self.html_formatter).decode('utf-8')
+            self.html_formatter)
+
+        # On Python 3, pygments.highlight() returns a bytes object, not a str.
+        if sys.version_info >= (3, 0):
+          html_highlighted = html_highlighted.decode('utf-8')
 
         # Take off the header and footer, these must be
         #   reapplied line-wise, within the page structure