DCE bugfix (#736)

* fix a dce bug where it is invalid to truncate a block if it leaves a final element with a bad type (wasm doesn't always allow removing unreachable code)

* add wast pass fuzzer

1 files changed, 136 insertions, 0 deletions

diff --git a/scripts/fuzz_passes_wast.py b/scripts/fuzz_passes_wast.py
new file mode 100644
index 000000000..5ec032de1
--- /dev/null
+++ b/scripts/fuzz_passes_wast.py
@@ -0,0 +1,136 @@
+#! /usr/bin/env python
+
+#   Copyright 2016 WebAssembly Community Group participants
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+
+'''
+This fuzzes passes, by starting with a wast, then running
+random passes on the wast, and seeing if they break optimization
+or validation
+
+Usage: Provide the filename of the wast.
+'''
+
+import os
+import random
+import shutil
+import subprocess
+import sys
+
+PASSES = [
+    "duplicate-function-elimination",
+    "dce",
+    "remove-unused-brs",
+    "remove-unused-names",
+    "optimize-instructions",
+    "precompute",
+    "simplify-locals",
+    "vacuum",
+    "coalesce-locals",
+    "reorder-locals",
+    "merge-blocks",
+    "remove-unused-functions",
+]
+
+# main
+
+wast = sys.argv[1]
+print '>>> wast:', wast
+
+args = sys.argv[2:]
+
+
+def run():
+  try:
+    print 'run', ['bin/wasm-opt', wast]
+    subprocess.check_call(['bin/wasm-opt', wast])
+  except Exception, e:
+    print ">>> !!! ", e, " !!!"
+  return 'ok'
+
+original_wast = None
+
+try:
+  # get normal output
+
+  normal = run()
+  print '>>> normal output:\n', normal
+  assert normal, 'must be output'
+
+  # ensure we actually use the wast
+
+  original_wast = wast + '.original.wast'
+  shutil.move(wast, original_wast)
+
+  def apply_passes(passes):
+    wasm_opt = os.path.join('bin', 'wasm-opt')
+    subprocess.check_call([wasm_opt, original_wast] + passes + ['-o', wast],
+                          stderr=open('/dev/null'))
+
+  # loop, looking for failures
+
+  def simplify(passes):
+    # passes is known to fail, try to simplify down by removing
+    more = True
+    while more:
+      more = False
+      print '>>> trying to reduce:', ' '.join(passes),
+      print '  [' + str(len(passes)) + ']'
+      for i in range(len(passes)):
+        smaller = passes[:i] + passes[i + 1:]
+        print '>>>>>> try to reduce to:', ' '.join(smaller),
+        print '  [' + str(len(smaller)) + ']'
+        try:
+          apply_passes(smaller)
+          assert run() == normal
+        except:
+          # this failed too, so it's a good reduction
+          passes = smaller
+          print '>>> reduction successful'
+          more = True
+          break
+    print '>>> reduced to:', ' '.join(passes)
+
+  tested = set()
+
+  def pick_passes():
+    ret = []
+    while 1:
+      str_ret = str(ret)
+      if random.random() < 0.5 and str_ret not in tested:
+        tested.add(str_ret)
+        return ret
+      ret.append('--' + random.choice(PASSES))
+
+  counter = 0
+
+  while 1:
+    passes = pick_passes()
+    print '>>> [' + str(counter) + '] testing:', ' '.join(passes)
+    counter += 1
+    try:
+      apply_passes(passes)
+    except Exception, e:
+      print e
+      simplify(passes)
+      break
+    seen = run()
+    if seen != normal:
+      print '>>> bad output:\n', seen
+      simplify(passes)
+      break
+
+finally:
+  if original_wast:
+    shutil.move(original_wast, wast)