PGO and LTO in clang-cl

build/pgo/llvm_pgo.py

@@ -0,0 +1,43 @@
+# 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/.
+
+"""Collect LLVM profiles outside the directories cleaned between PGO passes."""
+
+import glob
+import os
+import subprocess
+import tempfile
+
+
+class LLVMProfile(object):
+    def __init__(self, topobjdir, profdata):
+        if not profdata or not os.path.isfile(profdata):
+            raise RuntimeError("clang-cl PGO requires a configured llvm-profdata")
+        self.topobjdir = os.path.abspath(topobjdir)
+        self.profdata = profdata
+        self.output = os.path.join(self.topobjdir, 'merged.profdata')
+        self.directory = None
+
+    def prepare(self, env):
+        # Never reuse a previous training run's merged or raw profiles.
+        if os.path.exists(self.output):
+            os.remove(self.output)
+        self.directory = tempfile.mkdtemp(prefix='pgo-profiles-', dir=self.topobjdir)
+        # %m distinguishes instrumented DLLs; %p distinguishes child processes.
+        env['LLVM_PROFILE_FILE'] = os.path.join(self.directory, '%m-%p.profraw')
+
+    def merge(self):
+        profiles = sorted(glob.glob(os.path.join(self.directory, '*.profraw')))
+        if not profiles or not any(os.path.getsize(p) for p in profiles):
+            raise RuntimeError("PGO training produced no LLVM profile data")
+        # An input list avoids Windows command-line length limits. Keep profiles
+        # on failure so that corrupt or incompatible data can be diagnosed.
+        inputs = os.path.join(self.directory, 'profiles.list')
+        with open(inputs, 'w') as stream:
+            for profile in profiles:
+                stream.write(profile + '\n')
+        subprocess.check_call([self.profdata, 'merge', '-o', self.output,
+                               '-f', inputs])
+        if not os.path.isfile(self.output) or not os.path.getsize(self.output):
+            raise RuntimeError("llvm-profdata did not produce a merged profile")