Makes |chrome_pgo_phase==2| use the downloaded profiles.

This integrates the PGO build config with the new gclient hooks added in
https://chromium-review.googlesource.com/c/chromium/src/+/2165448

Bug: 1056189
Change-Id: Ie165c3355496ac539836ee36903a51a1e585cbf1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107728Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763536}

build/config/compiler/BUILD.gn

@@ -1972,9 +1972,15 @@ config("default_stack_frames") {
 # Default "optimization on" config.
 config("optimize") {
   if (is_win) {
-    # Favor size over speed, /O1 must be before the common flags.
-    # /O1 implies /Os and /GF.
-    cflags = [ "/O1" ] + common_optimize_on_cflags + [ "/Oi" ]
+    if (chrome_pgo_phase != 2) {
+      # Favor size over speed, /O1 must be before the common flags.
+      # /O1 implies /Os and /GF.
+      cflags = [ "/O1" ] + common_optimize_on_cflags + [ "/Oi" ]
+    } else {
+      # PGO requires all translation units to be compiled with /O2. The actual
+      # optimization level will be decided based on the profiling data.
+      cflags = [ "/O2" ] + common_optimize_on_cflags + [ "/Oi" ]
+    }
   } else if (optimize_for_size && !is_nacl) {
     # Favor size over speed.
     # TODO(crbug.com/718650): Fix -Os in PNaCl compiler and remove the is_nacl

build/config/compiler/pgo/BUILD.gn

@@ -35,6 +35,28 @@ config("pgo_optimization_flags") {
   # Only add flags when chrome_pgo_phase == 2, so that variables we would use
   # are not required to be defined when we're not actually using PGO.
   if (chrome_pgo_phase == 2 && is_clang && !is_nacl && is_a_target_toolchain) {
+    _pgo_target = ""
+
+    if (is_win) {
+      if (target_cpu == "x64") {
+        _pgo_target = "win64"
+      } else {
+        _pgo_target = "win32"
+      }
+    } else if (is_mac) {
+      _pgo_target = "mac"
+    }
+
+    if (pgo_data_path == "" && _pgo_target != "") {
+      pgo_data_path = rebase_path(exec_script("//tools/update_pgo_profiles.py",
+                                              [
+                                                "--target",
+                                                _pgo_target,
+                                                "get_profile_path",
+                                              ],
+                                              "value"),
+                                  root_build_dir)
+    }
     assert(pgo_data_path != "",
            "Please set pgo_data_path to point at the profile data")
     cflags = [

build/dotfile_settings.gni

@@ -11,6 +11,7 @@ build_dotfile_settings = {
     "//build/config/android/internal_rules.gni",
     "//build/config/android/rules.gni",
     "//build/config/compiler/BUILD.gn",
+    "//build/config/compiler/pgo/BUILD.gn",
     "//build/config/gcc/gcc_version.gni",
     "//build/config/host_byteorder.gni",
     "//build/config/ios/ios_sdk.gni",