diff -r 000000000000 -r 6474c204b198 js/src/devtools/rootAnalysis/explain.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/devtools/rootAnalysis/explain.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,100 @@
+#!/usr/bin/python
+
+import re
+import argparse
+
+parser = argparse.ArgumentParser(description='Process some integers.')
+parser.add_argument('rootingHazards', nargs='?', default='rootingHazards.txt')
+parser.add_argument('gcFunctions', nargs='?', default='gcFunctions.txt')
+parser.add_argument('hazards', nargs='?', default='hazards.txt')
+parser.add_argument('extra', nargs='?', default='unnecessary.txt')
+parser.add_argument('refs', nargs='?', default='refs.txt')
+args = parser.parse_args()
+
+num_hazards = 0
+num_refs = 0
+try:
+    with open(args.rootingHazards) as rootingHazards, \
+        open(args.hazards, 'w') as hazards, \
+        open(args.extra, 'w') as extra, \
+        open(args.refs, 'w') as refs:
+        current_gcFunction = None
+
+        # Map from a GC function name to the list of hazards resulting from
+        # that GC function
+        hazardousGCFunctions = {}
+
+        # List of tuples (gcFunction, index of hazard) used to maintain the
+        # ordering of the hazards
+        hazardOrder = []
+
+        for line in rootingHazards:
+            m = re.match(r'^Time: (.*)', line)
+            mm = re.match(r'^Run on:', line)
+            if m or mm:
+                print >>hazards, line
+                print >>extra, line
+                print >>refs, line
+                continue
+
+            m = re.match(r'^Function.*has unnecessary root', line)
+            if m:
+                print >>extra, line
+                continue
+
+            m = re.match(r'^Function.*takes unsafe address of unrooted', line)
+            if m:
+                num_refs += 1
+                print >>refs, line
+                continue
+
+            m = re.match(r"^Function.*has unrooted.*of type.*live across GC call ('?)(.*?)('?) at \S+:\d+$", line)
+            if m:
+                # Function names are surrounded by single quotes. Field calls
+                # are unquoted.
+                current_gcFunction = m.group(2)
+                hazardousGCFunctions.setdefault(current_gcFunction, []).append(line)
+                hazardOrder.append((current_gcFunction, len(hazardousGCFunctions[current_gcFunction]) - 1))
+                num_hazards += 1
+                continue
+
+            if current_gcFunction:
+                if not line.strip():
+                    # Blank line => end of this hazard
+                    current_gcFunction = None
+                else:
+                    hazardousGCFunctions[current_gcFunction][-1] += line
+
+        with open(args.gcFunctions) as gcFunctions:
+            gcExplanations = {}  # gcFunction => stack showing why it can GC
+
+            current_func = None
+            explanation = None
+            for line in gcFunctions:
+                m = re.match(r'^GC Function: (.*)', line)
+                if m:
+                    if current_func:
+                        gcExplanations[current_func] = explanation
+                    current_func = None
+                    if m.group(1) in hazardousGCFunctions:
+                        current_func = m.group(1)
+                        explanation = line
+                elif current_func:
+                    explanation += line
+            if current_func:
+                gcExplanations[current_func] = explanation
+
+            for gcFunction, index in hazardOrder:
+                gcHazards = hazardousGCFunctions[gcFunction]
+                if gcFunction in gcExplanations:
+                    print >>hazards, (gcHazards[index] + gcExplanations[gcFunction])
+                else:
+                    print >>hazards, gcHazards[index]
+
+except IOError as e:
+    print 'Failed: %s' % str(e)
+
+print("Wrote %s" % args.hazards)
+print("Wrote %s" % args.extra)
+print("Wrote %s" % args.refs)
+print("Found %d hazards and %d unsafe references" % (num_hazards, num_refs))