[Coverage] Enable merging coverage data from swarming.

This adds a function to the sancov_merger that merges the
output files of one swarming shard in parallel. This will
be called from the infrastructure when collecting/merging
swarming results.

The tool will be called subsequently for each shard. On
the first call, the target dir will be empty and the sancov
files will just be moved.

BUG=chromium:568949
LOG=n
NOTRY=true

Review URL: https://codereview.chromium.org/1782843002

Cr-Commit-Position: refs/heads/master@{#34678}

tools/sanitizers/sancov_merger.py

@@ -5,13 +5,16 @@
 
 """Script for merging sancov files in parallel.
 
-The sancov files are expected
+When merging test runner output, the sancov files are expected
 to be located in one directory with the file-name pattern:
 <executable name>.test.<id>.sancov
 
 For each executable, this script writes a new file:
 <executable name>.result.sancov
 
+When --swarming-output-dir is specified, this script will merge the result
+files found there into the coverage folder.
+
 The sancov tool is expected to be in the llvm compiler-rt third-party
 directory. It's not checked out by default and must be added as a custom deps:
 'v8/third_party/llvm/projects/compiler-rt':
@@ -47,6 +50,9 @@ CPUS = cpu_count()
 # executable name in group 1.
 SANCOV_FILE_RE = re.compile(r'^(.*)\.test\.\d+\.sancov$')
 
+# Regexp to find sancov result files as returned from swarming.
+SANCOV_RESULTS_FILE_RE = re.compile(r'^.*\.result\.sancov$')
+
 
 def merge(args):
   """Merge several sancov files into one.
@@ -110,27 +116,16 @@ def generate_inputs(keep, coverage_dir, file_map, cpus):
   return inputs
 
 
-def merge_parallel(inputs):
+def merge_parallel(inputs, merge_fun=merge):
   """Process several merge jobs in parallel."""
   pool = Pool(CPUS)
   try:
-    return pool.map(merge, inputs)
+    return pool.map(merge_fun, inputs)
   finally:
     pool.close()
 
 
-def main():
-  parser = argparse.ArgumentParser()
-  parser.add_argument('--coverage-dir', required=True,
-                      help='Path to the sancov output files.')
-  parser.add_argument('--keep', default=False, action='store_true',
-                      help='Keep sancov output files after merging.')
-  options = parser.parse_args()
-
-  # Check if folder with coverage output exists.
-  assert (os.path.exists(options.coverage_dir) and
-          os.path.isdir(options.coverage_dir))
-
+def merge_test_runner_output(options):
   # Map executable names to their respective sancov files.
   file_map = {}
   for f in os.listdir(options.coverage_dir):
@@ -160,6 +155,73 @@ def main():
   logging.info('Merging %d intermediate results.' % len(inputs))
 
   merge_parallel(inputs)
+
+
+def merge_two(args):
+  """Merge two sancov files.
+
+  Called trough multiprocessing pool. The args are expected to unpack to:
+    swarming_output_dir: Folder where to find the new file.
+    coverage_dir: Folder where to find the existing file.
+    f: File name of the file to be merged.
+  """
+  swarming_output_dir, coverage_dir, f = args
+  input_file = os.path.join(swarming_output_dir, f)
+  output_file = os.path.join(coverage_dir, f)
+  process = subprocess.Popen(
+      [SANCOV_TOOL, 'merge', input_file, output_file],
+      stdout=subprocess.PIPE,
+      stderr=subprocess.PIPE,
+  )
+  output, _ = process.communicate()
+  assert process.returncode == 0
+  with open(output_file, "wb") as f:
+    f.write(output)
+
+
+def merge_swarming_output(options):
+  # Iterate sancov files from swarming.
+  files = []
+  for f in os.listdir(options.swarming_output_dir):
+    match = SANCOV_RESULTS_FILE_RE.match(f)
+    if match:
+      if os.path.exists(os.path.join(options.coverage_dir, f)):
+        # If the same file already exists, we'll merge the data.
+        files.append(f)
+      else:
+        # No file yet? Just move it.
+        os.rename(os.path.join(options.swarming_output_dir, f),
+                  os.path.join(options.coverage_dir, f))
+
+  inputs = [(options.swarming_output_dir, options.coverage_dir, f)
+            for f in files]
+
+  logging.info('Executing %d merge jobs in parallel.' % len(inputs))
+  merge_parallel(inputs, merge_two)
+
+
+def main():
+  parser = argparse.ArgumentParser()
+  parser.add_argument('--coverage-dir', required=True,
+                      help='Path to the sancov output files.')
+  parser.add_argument('--keep', default=False, action='store_true',
+                      help='Keep sancov output files after merging.')
+  parser.add_argument('--swarming-output-dir',
+                      help='Folder containing a results shard from swarming.')
+  options = parser.parse_args()
+
+  # Check if folder with coverage output exists.
+  assert (os.path.exists(options.coverage_dir) and
+          os.path.isdir(options.coverage_dir))
+
+  if options.swarming_output_dir:
+    # Check if folder with swarming output exists.
+    assert (os.path.exists(options.swarming_output_dir) and
+            os.path.isdir(options.swarming_output_dir))
+    merge_swarming_output(options)
+  else:
+    merge_test_runner_output(options)
+
   return 0