Index: utils/opt-viewer/opt-viewer.py
===================================================================
--- utils/opt-viewer/opt-viewer.py
+++ utils/opt-viewer/opt-viewer.py
@@ -13,9 +13,14 @@
 # Try to use the C parser.
 try:
     from yaml import CLoader as Loader
+    # no GIL contention means multithreading should work
+    from multiprocessing.pool import ThreadPool as Pool
 except ImportError:
     from yaml import Loader
+    from multiprocessing import Pool
 import argparse
+import os
+import errno
 import os.path
 import re
 import subprocess
@@ -23,6 +28,7 @@
 from pygments import highlight
 from pygments.lexers.c_cpp import CppLexer
 from pygments.formatters import HtmlFormatter
+import time
 
 parser = argparse.ArgumentParser(description=desc)
 parser.add_argument('yaml_files', nargs='+')
@@ -176,7 +182,7 @@
 </html>
             '''.format(filename), file=self.stream)
 
-        self.html_formatter = HtmlFormatter()
+        self.html_formatter = HtmlFormatter(encoding='utf-8')
         self.cpp_lexer = CppLexer()
 
     def render_source_line(self, linenum, line):
@@ -278,41 +284,85 @@
 </html>''', file=self.stream)
 
 
-all_remarks = dict()
-file_remarks = dict()
 
-for input_file in args.yaml_files:
-    f = open(input_file)
-    docs = yaml.load_all(f, Loader=Loader)
-    for remark in docs:
-        # Avoid remarks withoug debug location or if they are duplicated
-        if not hasattr(remark, 'DebugLoc') or remark.key in all_remarks:
-            continue
-        all_remarks[remark.key] = remark
+import functools
+from collections import defaultdict
+def get_remarks(input_file):
+    max_hotness = 0
+    all_remarks = dict()
+    file_remarks = defaultdict(functools.partial(defaultdict, list))
+
+    with open(input_file) as f:
+        docs = yaml.load_all(f, Loader=Loader)
 
-        file_remarks.setdefault(remark.File, dict()).setdefault(remark.Line, []).append(remark)
+        for remark in docs:
+            # Avoid remarks withoug debug location or if they are duplicated
+            if not hasattr(remark, 'DebugLoc') or remark.key in all_remarks:
+                continue
+            all_remarks[remark.key] = remark
 
-        Remark.max_hotness = max(Remark.max_hotness, remark.Hotness)
+            file_remarks[remark.File][remark.Line].append(remark)
 
-# Set up a map between function names and their source location for function where inlining happened
-for remark in all_remarks.itervalues():
-    if type(remark) == Passed and remark.Pass == "inline" and remark.Name == "Inlined":
-        for arg in remark.Args:
-            caller = arg.get('Caller')
-            if caller:
-                    Remark.caller_loc[caller] = arg['DebugLoc']
+            max_hotness = max(max_hotness, remark.Hotness)
 
-if Remark.should_display_hotness():
-    sorted_remarks = sorted(all_remarks.itervalues(), key=lambda r: r.Hotness, reverse=True)
-else:
-    sorted_remarks = sorted(all_remarks.itervalues(), key=lambda r: (r.File, r.Line, r.Column))
+    return max_hotness, all_remarks, file_remarks
 
-if not os.path.exists(args.output_dir):
-    os.mkdir(args.output_dir)
 
-for (filename, remarks) in file_remarks.iteritems():
+def render_file(entry):
+    filename, remarks = entry
     SourceFileRenderer(filename).render(remarks)
 
-IndexRenderer().render(sorted_remarks)
+if __name__ == '__main__':
+    t_begin = time.time()
+
+    t0 = time.time()
+    pool = Pool(processes=20)
+    all_remarks = dict()
+    file_remarks = defaultdict(functools.partial(defaultdict, list))
+    remarks = pool.map(get_remarks, args.yaml_files)
+
+    # merge results:
+    for hotness, all_rem, file_rem in remarks:
+        all_remarks.update(all_rem)
+        file_remarks.update(file_rem)
+        Remark.max_hotness = max(Remark.max_hotness, hotness)
+
+    t_end = time.time()
+    print('processed input files', t_end-t0, 'secs')
+
+    # Set up a map between function names and their source location for function where inlining happened
+    for remark in all_remarks.itervalues():
+        if type(remark) == Passed and remark.Pass == "inline" and remark.Name == "Inlined":
+            for arg in remark.Args:
+                caller = arg.get('Caller')
+                if caller:
+                        Remark.caller_loc[caller] = arg['DebugLoc']
+    t_end_map = time.time()
+    print('mapped remarks', t_end_map-t_end, 'secs')
+
+    if Remark.should_display_hotness():
+        sorted_remarks = sorted(all_remarks.itervalues(), key=lambda r: r.Hotness, reverse=True)
+    else:
+        sorted_remarks = sorted(all_remarks.itervalues(), key=lambda r: (r.File, r.Line, r.Column))
+
+    try:
+        os.makedirs(args.output_dir)
+    except OSError as e:
+        if e.errno == errno.EEXIST and os.path.isdir(args.output_dir):
+            pass
+        else:
+            raise
+
+    t0 = time.time()
+    pool.map(render_file, file_remarks.items())
+    t_end = time.time()
+
+    print('file rendering', t_end-t0, 'sec')
+    IndexRenderer().render(sorted_remarks)
+    t_index_end = time.time()
+
+    print('index rendering', t_index_end - t_end, 'sec')
+    shutil.copy(os.path.join(os.path.dirname(os.path.realpath(__file__)), "style.css"), args.output_dir)
 
-shutil.copy(os.path.join(os.path.dirname(os.path.realpath(__file__)), "style.css"), args.output_dir)
+    t_ultimate_end = time.time()
+    print('total time', t_ultimate_end - t_begin, 'secs')