Add Link-Time Optimizations support for Android.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 614 matching lines @@
       'enable_load_completion_hacks%': 1,
 
       # Automatically select platforms under ozone. Turn this off to
       # build only explicitly selected platforms.
       'ozone_auto_platforms%': 1,
 
       # If this is set clang is used as host compiler, but not as target
       # compiler. Always do this by default.
       'host_clang%': 1,
 
+      # Link-Time Optimizations
+      # crbug.com/407544
+      'use_lto%': 0,
+      # Enable LTO on code compiled with -O2.
+      # Do not merge both options as that will result with the whole

[tomhudson, 2014/10/13 16:41:11]

Not quite clear to me reading this what "merge both options" means (and you've
used the same phrasing elsewhere) - what am I not supposed to do?

Not *use* both options?
Refactor the gyp to combine the two options as one somehow?
Something else?

[Fabrice (no longer in Chrome), 2014/10/14 14:58:55]

Do not use both options at the same time, I fail at typing.

+      # code being optimized with -O2 due to the way LTO merges optimization
+      # flags at link-time.
+      'use_lto_o2%': 0,
+
       'conditions': [
         # A flag for POSIX platforms
         ['OS=="win"', {
           'os_posix%': 0,
         }, {
           'os_posix%': 1,
         }],
 
         # A flag for BSD platforms
         ['OS=="freebsd" or OS=="openbsd"', {
@@ skipping 527 matching lines @@
     'spdy_proxy_auth_property%': '<(spdy_proxy_auth_property)',
     'spdy_proxy_auth_value%': '<(spdy_proxy_auth_value)',
     'enable_mdns%' : '<(enable_mdns)',
     'enable_service_discovery%' : '<(enable_service_discovery)',
     'enable_wifi_bootstrapping%': '<(enable_wifi_bootstrapping)',
     'enable_hangout_services_extension%' : '<(enable_hangout_services_extension)',
     'v8_optimized_debug%': '<(v8_optimized_debug)',
     'proprietary_codecs%': '<(proprietary_codecs)',
     'use_goma%': '<(use_goma)',
     'gomadir%': '<(gomadir)',
+    'use_lto%': '<(use_lto)',
+    'use_lto_o2%': '<use_lto_o2',
     'video_hole%': '<(video_hole)',
     'enable_load_completion_hacks%': '<(enable_load_completion_hacks)',
     'support_pre_M6_history_database%': '<(support_pre_M6_history_database)',
 
     # Whether or not we are building the Athena shell.
     'use_athena%': '0',
 
     # Use system protobuf instead of bundled one.
     'use_system_protobuf%': 0,
 
@@ skipping 1104 matching lines @@
       # Do not disable seccomp_bpf anywhere without talking to
       # security@chromium.org!
       ['((OS=="linux" or OS=="android") and '
            '(target_arch=="ia32" or target_arch=="x64" or '
              'target_arch=="arm" or target_arch=="mipsel" or '
              'target_arch=="arm64"))', {
          'use_seccomp_bpf%': 1,
       }, {
          'use_seccomp_bpf%': 0,
       }],
+      # Set component build with LTO until all tests pass.

[tomhudson, 2014/10/13 16:41:11]

"Until all tests pass" - does this mean they don't pass yet? Or are this comment
or condition block obsolete?

[Fabrice (no longer in Chrome), 2014/10/14 14:58:55]

Yes, there are many code generation and link bugs with LTO. We have a bot in the
works to compile the code and run tests which we are going to use to track
regressions and file bugs against GCC.

+      # This also reduces link time.
+      ['use_lto==1', {
+        'component%': "shared_library",
+      }],
     ],
 
     # older history files use fts2 instead of fts3
     'sqlite_enable_fts2%': '<(support_pre_M6_history_database)',
 
     # The path to the ANGLE library.
     'angle_path': '<(DEPTH)/third_party/angle',
 
     # List of default apps to install in new profiles.  The first list contains
     # the source files as found in svn.  The second list, used only for linux,
@@ skipping 1422 matching lines @@
                       '-target arm-linux-gnueabihf',
                     ],
                     'ldflags': [
                       '-target arm-linux-gnueabihf',
                     ],
                   }],
                   ['arm_arch!=""', {
                     'cflags': [
                       '-march=<(arm_arch)',
                     ],
+                    'conditions': [
+                      ['use_lto==1 or use_lto_o2==1', {
+                        'ldflags': [
+                          '-march=<(arm_arch)',
+                        ],
+                      }],
+                    ],
                   }],
                   ['clang==1 and OS!="android"', {
                     'cflags': [
                       # We need to disable clang's builtin assembler as it can't
                       # handle several asm files, crbug.com/124610
                       '-no-integrated-as',
                     ],
                   }],
                   ['arm_tune!=""', {
                     'cflags': [
                       '-mtune=<(arm_tune)',
                     ],
+                    'conditions': [
+                      ['use_lto==1 or use_lto_o2==1', {
+                        'ldflags': [
+                          '-mtune=<(arm_tune)',
+                        ],
+                      }],
+                    ],
                   }],
                   ['arm_fpu!=""', {
                     'cflags': [
                       '-mfpu=<(arm_fpu)',
                     ],
+                    'conditions': [
+                      ['use_lto==1 or use_lto_o2==1', {
+                        'ldflags': [
+                          '-mfpu=<(arm_fpu)',
+                        ],
+                      }],
+                    ],
                   }],
                   ['arm_float_abi!=""', {
                     'cflags': [
                       '-mfloat-abi=<(arm_float_abi)',
                     ],
+                    'conditions': [
+                      ['use_lto==1 or use_lto_o2==1', {
+                        'ldflags': [
+                          '-mfloat-abi=<(arm_float_abi)',
+                        ],
+                      }],
+                    ],
                   }],
                   ['arm_thumb==1', {
                     'cflags': [
                       '-mthumb',
                     ],
+                    'conditions': [
+                      ['use_lto==1 or use_lto_o2==1', {
+                        'ldflags': [
+                          '-mthumb',
+                        ],
+                      }],
+                    ],
                   }],
                   ['OS=="android"', {
                     # Most of the following flags are derived from what Android
                     # uses by default when building for arm, reference for which
                     # can be found in the following file in the Android NDK:
                     # toolchains/arm-linux-androideabi-4.9/setup.mk
                     'cflags': [
                       # The tree-sra optimization (scalar replacement for
                       # aggregates enabling subsequent optimizations) leads to
                       # invalid code generation when using the Android NDK's
@@ skipping 1874 matching lines @@
     #  make generator doesn't support CC_wrapper without CC
     #  in make_global_settings yet.
     ['use_goma==1 and ("<(GENERATOR)"=="ninja" or clang==1)', {
       'make_global_settings': [
        ['CC_wrapper', '<(gomadir)/gomacc'],
        ['CXX_wrapper', '<(gomadir)/gomacc'],
        ['CC.host_wrapper', '<(gomadir)/gomacc'],
        ['CXX.host_wrapper', '<(gomadir)/gomacc'],
       ],
     }],
+    ['use_lto==1', {
+      'target_defaults': {
+        'target_conditions': [
+          ['_toolset=="target"', {
+            'cflags': [
+              '-flto',
+              '-ffat-lto-objects',
+            ],
+          }],
+        ],
+      },
+    }],
+    ['use_lto==1 or use_lto_o2==1', {
+      'target_defaults': {
+        'target_conditions': [
+          ['_toolset=="target"', {
+            'ldflags': [
+              '-flto=32',
+            ],
+          }],
+        ],
+      },
+    }],
   ],
   'xcode_settings': {
     # DON'T ADD ANYTHING NEW TO THIS BLOCK UNLESS YOU REALLY REALLY NEED IT!
     # This block adds *project-wide* configuration settings to each project
     # file.  It's almost always wrong to put things here.  Specify your
     # custom xcode_settings in target_defaults to add them to targets instead.
 
     'conditions': [
       # In an Xcode Project Info window, the "Base SDK for All Configurations"
       # setting sets the SDK on a project-wide basis. In order to get the
@@ skipping 50 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }