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..aa0fc1be88e276e9ad83ab64b253c0a243c386ac 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -632,6 +632,15 @@
       # 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"', {
@@ -1179,6 +1188,8 @@
     '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 +2314,11 @@
       }, {
          '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
@@ -3745,6 +3761,13 @@
                     '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 +3780,49 @@
                     '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 +5717,29 @@
        ['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!