Add the possibility to build with PGO when using Clang

chrome/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/buildflag_header.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
+import("//build/config/compiler/pgo/pgo.gni")
 import("//build/config/features.gni")
 import("//build/config/locales.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build/config/win/console_app.gni")
 import("//build/config/win/manifest.gni")
 import("//build/toolchain/toolchain.gni")
 import("//chrome/chrome_paks.gni")
 import("//chrome/common/features.gni")
 import("//chrome/process_version_rc_template.gni")
@@ skipping 91 matching lines @@
     }
   }
 
   executable("chrome_initial") {
     if (is_win) {
       output_name = "initialexe/chrome"
     } else {
       output_name = "chrome"
     }
 
+    if (!is_win || is_clang) {
+      # Normally, we need to pass specific flags to the linker to
+      # create an executable that gathers profile data. However, when
+      # using MSVC, we need to make sure we *don't* pass /GENPROFILE
+      # when linking without generating any code, or else the linker
+      # will give us fatal error LNK1264. So we add the PGO flags
+      # on all configurations, execpt MSVC on Windows.
+      configs += [ "//build/config/compiler/pgo:default_pgo_flags" ]

[Sébastien Marchand, 2016/11/24 15:57:07]

This config will be applied to chrome.exe, do you also want to apply it to the
'main_dll' target (for the Clang build only).

Again, I really think that this should be behind a "if (chrome_pgo_phase > 0)"
condition. Debugging an error caused by someone adding some default flag to the
PGO config will probably be tricky, so it's probably better to add some more
safety checks.

+    }
+
     # Because the sources list varies so significantly per-platform, generally
     # each platform lists its own files rather than relying on filtering or
     # removing unused files.
     sources = [
       "app/chrome_exe_resource.h",
     ]
     defines = []
     public_deps = []
     deps = [
       "//build/config/sanitizers:deps",
@@ skipping 289 matching lines @@
         "/DELAYLOAD:wininet.dll",
       ]
 
       if (symbol_level == 2) {
         # Incremental linking doesn't work on this target in debug mode with
         # full symbols, but does work in other cases, including minimal
         # symbols.
         configs -= [ "//build/config/win:default_incremental_linking" ]
         configs += [ "//build/config/win:no_incremental_linking" ]
       }
-      if (chrome_pgo_phase == 1) {
-        ldflags += [
-          "/LTCG",
-
-          # Make sure that enough memory gets allocated for the PGO profiling
-          # buffers and also cap this memory. Usually a PGI instrumented build
-          # of chrome_child.dll requires ~55MB of memory for storing its counter
-          # etc, normally the linker should automatically choose an appropriate
-          # amount of memory but it doesn't always do a good estimate and
-          # sometime allocates too little or too much (and so the instrumented
-          # image fails to start). Making sure that the buffer has a size in the
-          # [128 MB, 512 MB] range should prevent this from happening.
-          "/GENPROFILE:MEMMIN=134217728",
-          "/GENPROFILE:MEMMAX=536870912",
-          "/PogoSafeMode",
-        ]
-      } else if (chrome_pgo_phase == 2) {
-        ldflags += [
-          "/LTCG",
-          "/USEPROFILE",
-        ]
-      }
+      configs += [ "//build/config/compiler/pgo:default_pgo_flags" ]
 
       if (enable_plugins && enable_pdf) {
         deps += [ "//pdf" ]
       }
     }
   }
   copy("copy_first_run") {
     sources = [
       "app/firstRun",
     ]
@@ skipping 1152 matching lines @@
       "//chrome/app/theme/$branding_path_component/product_logo_48.png",
       "//chrome/tools/build/linux/chrome-wrapper",
       "//third_party/xdg-utils/scripts/xdg-mime",
       "//third_party/xdg-utils/scripts/xdg-settings",
     ]
     outputs = [
       "$root_out_dir/{{source_file_part}}",
     ]
   }
 }