zircon/public/gn/config/lto/BUILD.gn

# Copyright 2019 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

config("lto") {
  compiler_flags = [
    "-flto",

    # Enable whole-program devirtualization and virtual constant propagation.
    "-fwhole-program-vtables",
  ]
}

declare_args() {
  # Number of parallel ThinLTO jobs.
  thinlto_jobs = 8

  # ThinLTO cache directory path.
  thinlto_cache_dir = rebase_path("$root_out_dir/thinlto-cache", root_build_dir)
}

config("thinlto") {
  compiler_flags = [ "-flto=thin" ]
  ldflags = [
    # The ThinLTO driver launches a number of threads in parallel whose
    # number is by default equivalent to the number of cores.  We need
    # to limit the parallelism to avoid aggressive competition between
    # different linker jobs.
    "-Wl,--thinlto-jobs=$thinlto_jobs",

    # Set the ThinLTO cache directory which is used to cache native
    # object files for ThinLTO incremental builds.  This directory is
    # not managed by Ninja and has to be cleaned manually, but it is
    # periodically garbage-collected by the ThinLTO driver.
    "-Wl,--thinlto-cache-dir=$thinlto_cache_dir",
  ]
}