Add Link-Time Optimizations support for Android.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 1aa13d3dc9cbd0a2fe1362e728c9121728bf05c5..c3a614d635aec2aa2bd372e4adc68693d476042b 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -632,6 +632,11 @@
       # compiler. Always do this by default.
       'host_clang%': 1,
 
+      # Link-Time Optimizations
+      # crbug.com/407544
+      'use_lto%': 0,
+      'use_lto_o2%': 0,

[pasko, 2014/10/10 11:59:21]

it's worth explaining what use_lto_o2 is. Does use_lto work? In the issues
description please explain what the current state of the things are: which
targets build, which tests are known to pass/fail in each configuration.

[Fabrice (no longer in Chrome), 2014/10/13 15:45:12]

Done.

+
       'conditions': [
         # A flag for POSIX platforms
         ['OS=="win"', {
@@ -1179,6 +1184,8 @@
     '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)',
@@ -2303,6 +2310,11 @@
       }, {
          'use_seccomp_bpf%': 0,
       }],
+      # Set component build with LTO until all tests pass.
+      # This reduces link time

[pasko, 2014/10/10 11:59:21]

nit:

s/This reduces link time/This reduces link time./

[Fabrice (no longer in Chrome), 2014/10/13 15:45:12]

Done.

+      ['use_lto==1', {
+        'component%': "shared_library",
+      }],
     ],
 
     # older history files use fts2 instead of fts3
@@ -3745,6 +3757,13 @@
                     'cflags': [
                       '-march=<(arm_arch)',
                     ],
+                    'conditions': [
+                      ['use_lto==1 or use_lto_o2==1', {
+                        'ldflags': [
+                          '-march=<(arm_arch)',
+                        ],
+                      }],
+                    ],
                   }],
                   ['clang==1 and OS!="android"', {
                     'cflags': [
@@ -3757,21 +3776,49 @@
                     '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
@@ -5666,6 +5713,29 @@
        ['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!