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diff --git a/tools/jprof/split-profile.py b/tools/jprof/split-profile.py
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+#!/usr/bin/python
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This program splits up a jprof profile into multiple files based on a
+# list of functions in a text file.  First, a complete profile is
+# generated.  Then, for each line in the text file, a profile is
+# generated containing only stacks that go through that line, and also
+# excluding all stacks in earlier lines in the text file.  This means
+# that the text file, from start to end, is splitting out pieces of the
+# profile in their own file.  Finally, a final profile containing the
+# remainder is produced.
+
+# The program takes four arguments:
+#   (1) The path to jprof.
+#   (2) The path to the text file describing the splits.  The output
+#       will be placed in the same directory as this file.
+#   (3) The program that was profiled.
+#   (4) The jprof-log file generated by the profile, to be split up.
+# (Really, all arguments from (3) and later are passed through to
+# jprof, so additional arguments could be provided if you want to pass
+# additional arguments to jprof.)
+
+# In slightly more detail:
+#
+# This script uses jprof's includes (-i) and excludes (-e) options to
+# split profiles into segments.  It takes as input a single text file,
+# and from that text file creates a series of jprof profiles in the
+# directory the text file is in.
+#
+# The input file format looks like the following:
+#
+#   poll g_main_poll
+#   GetRuleCascade CSSRuleProcessor::GetRuleCascade(nsPresContext *, nsAtom *)
+#   RuleProcessorData RuleProcessorData::RuleProcessorData
+#        (nsPresContext *, nsIContent *, nsRuleWalker *, nsCompatibility *)
+#
+#
+# From this input file, the script will construct a profile called
+# jprof-0.html that contains the whole profile, a profile called
+# jprof-1-poll.html that includes only stacks with g_main_poll, a
+# profile called jprof-2-GetRuleCascade.html that includes only stacks
+# that have GetRuleCascade and do not have g_main_poll, a profile called
+# jprof-3-RuleProcessorData.html that includes only stacks that have the
+# RuleProcessorData constructor and do not have GetRuleCascade or
+# g_main_poll, and a profile called jprof-4.html that includes only
+# stacks that do not have any of the three functions in them.
+#
+# This means that all of the segments of the profile, except
+# jprof-0.html, are mutually exclusive.  Thus clever ordering of the
+# functions in the input file can lead to a logical splitting of the
+# profile into segments.
+
+import os.path
+import subprocess
+import sys
+
+if len(sys.argv) < 5:
+    sys.stderr.write("Expected arguments: <jprof> <split-file> <program> <jprof-log>\n")
+    sys.exit(1)
+
+jprof = sys.argv[1]
+splitfile = sys.argv[2]
+passthrough = sys.argv[3:]
+
+for f in [jprof, splitfile]:
+    if not os.path.isfile(f):
+        sys.stderr.write("could not find file: {0}\n".format(f))
+        sys.exit(1)
+
+
+def read_splits(splitfile):
+    """
+    Read splitfile (each line of which contains a name, a space, and
+    then a function name to split on), and return a list of pairs
+    representing exactly that.  (Note that the name cannot contain
+    spaces, but the function name can, and often does.)
+    """
+
+    def line_to_split(line):
+        line = line.strip("\r\n")
+        idx = line.index(" ")
+        return (line[0:idx], line[idx + 1 :])
+
+    io = open(splitfile, "r")
+    result = [line_to_split(line) for line in io]
+    io.close()
+    return result
+
+
+splits = read_splits(splitfile)
+
+
+def generate_profile(options, destfile):
+    """
+    Run jprof to generate one split of the profile.
+    """
+    args = [jprof] + options + passthrough
+    print("Generating {}".format(destfile))
+    destio = open(destfile, "w")
+    # jprof expects the "jprof-map" file to be in its current working directory
+    cwd = None
+    for option in passthrough:
+        if option.find("jprof-log"):
+            cwd = os.path.dirname(option)
+    if cwd is None:
+        raise Exception("no jprof-log option given")
+    process = subprocess.Popen(args, stdout=destio, cwd=cwd)
+    process.wait()
+    destio.close()
+    if process.returncode != 0:
+        os.remove(destfile)
+        sys.stderr.write(
+            "Error {0} from command:\n  {1}\n".format(
+                process.returncode, " ".join(args)
+            )
+        )
+        sys.exit(process.returncode)
+
+
+def output_filename(number, splitname):
+    """
+    Return the filename (absolute path) we should use to output the
+    profile segment with the given number and splitname.  Splitname
+    should be None for the complete profile and the remainder.
+    """
+
+    def pad_count(i):
+        result = str(i)
+        # 0-pad to the same length
+        result = "0" * (len(str(len(splits) + 1)) - len(result)) + result
+        return result
+
+    name = pad_count(number)
+    if splitname is not None:
+        name += "-" + splitname
+
+    return os.path.join(os.path.dirname(splitfile), "jprof-{0}.html".format(name))
+
+
+# generate the complete profile
+generate_profile([], output_filename(0, None))
+
+# generate the listed splits
+count = 1
+excludes = []
+for (splitname, splitfunction) in splits:
+    generate_profile(
+        excludes + ["-i" + splitfunction], output_filename(count, splitname)
+    )
+    excludes += ["-e" + splitfunction]
+    count = count + 1
+
+# generate the remainder after the splits
+generate_profile(excludes, output_filename(count, None))