Pass correct flags for use_lto==1 with Clang.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 644b7ad1cc0090757e1a0f30503c0f8e1c185238..c731d2ee8a36aeadfbec583ddfeaec6c45780199 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -2983,6 +2983,11 @@
       ['v8_use_external_startup_data==1', {
        'defines': ['V8_USE_EXTERNAL_STARTUP_DATA'],
       }],
+      ['use_lto==1 and (target_arch=="ia32" or target_arch=="x64")', {
+        # Required for third_party/zlib/crc_folding.c and various other code
+        # that uses SSE.
+        'ldflags+': ['-Wl,-plugin-opt,mcpu=corei7-avx'],

[Nico, 2015/01/29 18:48:01]

nit: i think you don't need the +, gyp merges lists by default

Isn't avx fairly new? I think we require cpus with SSE2, but not avx.

[pcc, 2015/01/29 19:11:13]

Done.
I'm not sure if there is a way to avoid this at the moment, as I've found that
LLVM LTO currently compiles all functions in the program for the same
sub-target. As I recall, LLVM has a concept of function-specific codegen
attributes to support this exact scenario, but for some reason it doesn't help
here. Eventually once this is fixed we should be able to remove this flag.

+      }],
     ],  # conditions for 'target_defaults'
     'target_conditions': [
       ['<(use_libpci)==1', {
@@ -5781,13 +5786,23 @@
           ['_toolset=="target"', {
             'cflags': [
               '-flto',
+            ],
+          }],
+        ],
+      },
+    }],
+    ['use_lto==1 and clang==0', {
+      'target_defaults': {
+        'target_conditions': [
+          ['_toolset=="target"', {
+            'cflags': [
               '-ffat-lto-objects',
             ],
           }],
         ],
       },
     }],
-    ['use_lto==1 or use_lto_o2==1', {
+    ['(use_lto==1 or use_lto_o2==1) and clang==0', {
       'target_defaults': {
         'target_conditions': [
           ['_toolset=="target"', {
@@ -5798,6 +5813,17 @@
         ],
       },
     }],
+    ['(use_lto==1 or use_lto_o2==1) and clang==1', {
+      'target_defaults': {
+        'target_conditions': [
+          ['_toolset=="target"', {
+            'ldflags': [
+              '-flto',

[Nico, 2015/01/29 18:48:01]

i'd be nice if gcc's and clang's flag here were compatible :-/

+            ],
+          }],
+        ],
+      },
+    }],
   ],
   'xcode_settings': {
     # DON'T ADD ANYTHING NEW TO THIS BLOCK UNLESS YOU REALLY REALLY NEED IT!