tools: add performance-log-related tools

performance-log-expand.py decodes a delta-encoded performance log
by expanding the deltas, producing a log where each sample (and
other relevant elements) contain complete information.  Note that
the structure of expanded logs is identical to that of delta-
encoded logs, the expanded log simply has no deltas.

performance-log-resolve.py resolves symbol information in
backtraces.  The logs produced by GIMP only specify the program
counter at each stack frame, providing an address-map to map
program-counter addresses to actual symbols separately.  This tool
looks up each program-counter address in the address map,
incorporating the relevant symbol information directly into the
backtrace.

Both tools read their input from STDIN, and write their output to
STDOUT, and can be chained in a pipeline (with
gimp-performance-log-expand.py appearing first).

Note that these tools require Python 3.

tools/performance-log-expand.py

@@ -0,0 +1,106 @@
+#!/usr/bin/env python3
+
+"""
+performance-log-expand.py -- Delta-decodes GIMP performance logs
+Copyright (C) 2018  Ell
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+
+Usage: performance-log-expand.py < infile > outfile
+"""
+
+from xml.etree import ElementTree
+import sys
+
+empty_element = ElementTree.Element ("")
+
+# Read performance log from STDIN
+log = ElementTree.fromstring (sys.stdin.buffer.read ())
+
+try:
+    has_backtrace = bool (int (log.find ("params").find ("backtrace").text))
+except:
+    has_backtrace = False
+
+def expand_simple (element, last_values):
+    last_values.update ({value.tag: value.text for value in element})
+
+    for value in list (element):
+        element.remove (value)
+
+    for tag, text in last_values.items ():
+        value = ElementTree.SubElement (element, tag)
+        value.text = text
+        value.tail = "\n"
+
+# Expand samples
+last_vars      = {}
+last_backtrace = {}
+
+for sample in (log.find ("samples") or empty_element).iterfind ("sample"):
+    # Expand variables
+    vars = sample.find ("vars") or \
+           ElementTree.SubElement (sample, "vars")
+
+    expand_simple (vars, last_vars)
+
+    # Expand backtrace
+    if has_backtrace:
+        backtrace = sample.find ("backtrace") or \
+                    ElementTree.SubElement (sample, "backtrace")
+
+        for thread in backtrace:
+            id     = thread.get ("id")
+            frames = list (thread)
+
+            if not frames:
+                last_backtrace.pop (id, None)
+            else:
+                last_thread = last_backtrace.setdefault (id, [None, []])
+                last_frames = last_thread[1]
+
+                name = thread.get ("name")
+                head = thread.get ("head")
+                tail = thread.get ("tail")
+
+                if head:
+                    frames = last_frames[:int (head)] + frames
+                if tail:
+                    frames = frames + last_frames[-int (tail):]
+
+                last_thread[0] = name
+                last_thread[1] = frames
+
+        for thread in list (backtrace):
+            backtrace.remove (thread)
+
+        for id, (name, frames) in last_backtrace.items ():
+            thread = ElementTree.SubElement (backtrace, "thread", id=id)
+            thread.text = "\n"
+            thread.tail = "\n"
+
+            if name:
+                thread.set ("name", name)
+
+            thread.extend (frames)
+
+# Expand address map
+last_address = {}
+
+for address in (log.find ("address-map") or empty_element).iterfind ("address"):
+    expand_simple (address, last_address)
+
+# Write performance log to STDOUT
+sys.stdout.buffer.write (ElementTree.tostring (log))