Require SSE2 for all 32-bit Linux builds and remove disable_sse2 option.

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 272 matching lines @@
       # Detect NEON support at run-time.
       'arm_neon_optional%': 0,
 
       # The system root for cross-compiles. Default: none.
       'sysroot%': '',
       'chroot_cmd%': '',
 
       # The system libdir used for this ABI.
       'system_libdir%': 'lib',
 
-      # On Linux, we build with sse2 for Chromium builds.
-      'disable_sse2%': 0,
-
       # Use libjpeg-turbo as the JPEG codec used by Chromium.
       'use_libjpeg_turbo%': 1,
 
       # Use system libjpeg. Note that the system's libjepg will be used even if
       # use_libjpeg_turbo is set.
       'use_system_libjpeg%': 0,
 
       # By default, component is set to static_library and it can be overriden
       # by the GYP command line or by ~/.gyp/include.gypi.
       'component%': 'static_library',
@@ skipping 1354 matching lines @@
       }],
 
       # Native Client glibc toolchain is enabled
       # by default except on arm and mips.
       ['target_arch=="arm" or target_arch=="mipsel"', {
         'disable_glibc%': 1,
       }, {
         'disable_glibc%': 0,
       }],
 
-      # Disable SSE2 when building for ARM or MIPS.
-      ['target_arch=="arm" or target_arch=="mipsel"', {
-        'disable_sse2%': 1,
-      }, {
-        'disable_sse2%': '<(disable_sse2)',
-      }],
-
       # Set the relative path from this file to the GYP file of the JPEG
       # library used by Chromium.
       ['use_system_libjpeg==1 or use_libjpeg_turbo==0', {
         # Configuration for using the system libjeg is here.
         'libjpeg_gyp_path': '../third_party/libjpeg/libjpeg.gyp',
       }, {
         'libjpeg_gyp_path': '../third_party/libjpeg_turbo/libjpeg.gyp',
       }],
 
       # Options controlling the use of GConf (the classic GNOME configuration
@@ skipping 1514 matching lines @@
                 # rounded to its original precision) but they have significant
                 # runtime performance penalty.
                 #
                 # -mfpmath=sse -msse2 makes the compiler use SSE instructions
                 # which keep floating-point values in SSE registers in its
                 # native precision (32-bit for single precision, and 64-bit
                 # for double precision values). This means the floating-point
                 # value used during computation does not change depending on
                 # how the compiler optimized the code, since the value is
                 # always kept in its specified precision.
+                #
+                # Refer to http://crbug.com/348761 for rationale behind SSE2
+                # being a minimum requirement for 32-bit Linux builds and
+                # http://crbug.com/313032 for an example where this has "bit"
+                # us in the past.
+                'cflags': [
+                  '-march=pentium4',

[Paweł Hajdan Jr., 2014/03/10 23:49:54]

Do we need to force -march=pentium4 here?

[scherkus (not reviewing), 2014/03/11 00:08:52]

As far as I can tell it was added in r12228 with most of the original Linux gyp
support.

agl@ questioned it in
https://codereview.chromium.org/1702009/diff/1/2#newcode925 as well.

I'm OK removing it.

[Paweł Hajdan Jr., 2014/03/11 00:28:16]

Thank you, looks good to me now.

+                  '-msse2',
+                  '-mfpmath=sse',
+                  '-mmmx',  # Allows mmintrin.h for MMX intrinsics.
+                  '-m32',
+                ],
+                'ldflags': [
+                  '-m32',
+                ],
                 'conditions': [
-                  ['branding=="Chromium" and disable_sse2==0', {
-                    'cflags': [
-                      '-march=pentium4',
-                      '-msse2',
-                      '-mfpmath=sse',
-                    ],
-                  }],
-                  # ChromeOS targets Pinetrail, which is sse3, but most of the
-                  # benefit comes from sse2 so this setting allows ChromeOS
-                  # to build on other CPUs.  In the future -march=atom would
-                  # help but requires a newer compiler.
-                  ['chromeos==1 and disable_sse2==0', {
-                    'cflags': [
-                      '-msse2',
-                      '-mfpmath=sse',
-                    ],
-                  }],
                   # Use gold linker for Android ia32 target.
                   ['OS=="android"', {
                     'cflags': [
                       '-fuse-ld=gold',
                     ],
                     'ldflags': [
                       '-fuse-ld=gold',
                     ],
                   }],
                   # Install packages have started cropping up with
                   # different headers between the 32-bit and 64-bit
                   # versions, so we have to shadow those differences off
                   # and make sure a 32-bit-on-64-bit build picks up the
                   # right files.
                   # For android build, use NDK headers instead of host headers
                   ['host_arch!="ia32" and OS!="android"', {
                     'include_dirs+': [
                       '/usr/include32',
                     ],
                   }],
                 ],
-                # -mmmx allows mmintrin.h to be used for mmx intrinsics.
-                # video playback is mmx and sse2 optimized.
-                'cflags': [
-                  '-m32',
-                  '-mmmx',
-                ],
-                'ldflags': [
-                  '-m32',
-                ],
               }],
             ],
           }],
           ['target_arch=="arm"', {
             'target_conditions': [
               ['_toolset=="target"', {
                 'cflags_cc': [
                   # The codesourcery arm-2009q3 toolchain warns at that the ABI
                   # has changed whenever it encounters a varargs function. This
                   # silences those warnings, as they are not helpful and
@@ skipping 1783 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',
   },
 }