Enable debug builds with some optimizations turned on.

build/toolchain.gypi

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 41 matching lines @@
     # Similar to vfp but on MIPS.
     'v8_can_use_fpu_instructions%': 'true',
 
     # Similar to the ARM hard float ABI but on MIPS.
     'v8_use_mips_abi_hardfloat%': 'true',
 
     # Default arch variant for MIPS.
     'mips_arch_variant%': 'mips32r2',
 
     'v8_enable_backtrace%': 0,
+
+    # Turns on compiler optimizations in Debug builds (#defines are unaffected).
+    'v8_optimized_debug%': 0,
+
     # Enable profiling support. Only required on Windows.
     'v8_enable_prof%': 0,
 
     # Some versions of GCC 4.5 seem to need -fno-strict-aliasing.
     'v8_no_strict_aliasing%': 0,
 
     # Chrome needs this definition unconditionally. For standalone V8 builds,
     # it's handled in build/standalone.gypi.
     'want_separate_host_toolset%': 1,
 
@@ skipping 357 matching lines @@
       'Debug': {
         'defines': [
           'DEBUG',
           'ENABLE_DISASSEMBLER',
           'V8_ENABLE_CHECKS',
           'OBJECT_PRINT',
           'VERIFY_HEAP',
         ],
         'msvs_settings': {
           'VCCLCompilerTool': {
-            'Optimization': '0',
-
             'conditions': [
-              ['OS=="win" and component=="shared_library"', {
+              ['component=="shared_library"', {
                 'RuntimeLibrary': '3',  # /MDd
               }, {
                 'RuntimeLibrary': '1',  # /MTd
               }],
+              ['v8_optimized_debug==1', {
+                'Optimization': '1',
+                'InlineFunctionExpansion': '2',
+                'EnableIntrinsicFunctions': 'true',
+                'FavorSizeOrSpeed': '0',
+                'StringPooling': 'true',
+                'BasicRuntimeChecks': '0',
+              }, {
+                'Optimization': '0',
+              }],
             ],
           },
           'VCLinkerTool': {
             'LinkIncremental': '2',
           },
         },
         'conditions': [
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd"', {
             'cflags': [ '-Wall', '<(werror)', '-W', '-Wno-unused-parameter',
                         '-Wnon-virtual-dtor', '-Woverloaded-virtual' ],
+            'conditions': [
+              ['v8_optimized_debug==1', {
+                'cflags!': [
+                  '-O0',
+                  '-O2',
+                  '-Os',
+                ],
+                'cflags': [
+                  '-fdata-sections',
+                  '-ffunction-sections',
+                  '-O1',
+                ],
+              }],
+              ['v8_optimized_debug==1 and gcc_version==44 and clang==0', {
+                'cflags': [
+                  # Avoid crashes with gcc 4.4 in the v8 test suite.
+                  '-fno-tree-vrp',
+                ],
+              }],
+            ],
           }],
           ['OS=="linux" and v8_enable_backtrace==1', {
             # Support for backtrace_symbols.
             'ldflags': [ '-rdynamic' ],
           }],
           ['OS=="android"', {
             'variables': {
               'android_full_debug%': 1,
             },
             'conditions': [
               ['android_full_debug==0', {
                 # Disable full debug if we want a faster v8 in a debug build.
                 # TODO(2304): pass DISABLE_DEBUG_ASSERT instead of hiding DEBUG.
                 'defines!': [
                   'DEBUG',
                 ],
               }],
             ],
           }],
           ['OS=="mac"', {
             'xcode_settings': {
-              'GCC_OPTIMIZATION_LEVEL': '0',  # -O0
+              'conditions': [
+                 ['v8_optimized_debug==1', {
+                   'GCC_OPTIMIZATION_LEVEL': '1',  # -O1
+                   'GCC_STRICT_ALIASING': 'YES',

[Nico, 2013/07/17 03:13:44]

Note that strict aliasing is only done at -O2 or higher (and on recent clangs
it's on by default with -O2 too). So setting GCC_STRICT_ALIASING here doesn't
really do anything.

+                 }, {
+                   'GCC_OPTIMIZATION_LEVEL': '0',  # -O0
+                 }],
+               ],
             },
           }],
         ],
       },  # Debug
       'Release': {
         'conditions': [
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd"', {
             'cflags!': [
               '-O2',
               '-Os',
@@ skipping 44 matching lines @@
           }],  # OS=="mac"
           ['OS=="win"', {
             'msvs_settings': {
               'VCCLCompilerTool': {
                 'Optimization': '2',
                 'InlineFunctionExpansion': '2',
                 'EnableIntrinsicFunctions': 'true',
                 'FavorSizeOrSpeed': '0',
                 'StringPooling': 'true',
                 'conditions': [
-                  ['OS=="win" and component=="shared_library"', {
+                  ['component=="shared_library"', {
                     'RuntimeLibrary': '2',  #/MD
                   }, {
                     'RuntimeLibrary': '0',  #/MT
                   }],
                   ['v8_target_arch=="x64"', {
                     # TODO(2207): remove this option once the bug is fixed.
                     'WholeProgramOptimization': 'true',
                   }],
                 ],
               },
               'VCLinkerTool': {
                 'LinkIncremental': '1',
                 'OptimizeReferences': '2',
                 'EnableCOMDATFolding': '2',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }