build: allow LTO with Clang 3.9.1+

Bug: #38568
Test: manual,
      - arm64-apple-darwin20.5.0 / Apple clang version 12.0.5 (clang-1205.0.22.9)
      - x86_64-pc-linux-gnu / Ubuntu clang version 13.0.0-++20210520052624+48780527dd68-1~exp1~20210520153429.417
Signed-off-by: Jesse Chan <jc@linux.com>

PR-URL: #38751
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

common.gypi

@@ -164,17 +164,28 @@
           'v8_enable_handle_zapping': 0,
           'pgo_generate': ' -fprofile-generate ',
           'pgo_use': ' -fprofile-use -fprofile-correction ',
-          'lto': ' -flto=4 -fuse-linker-plugin -ffat-lto-objects ',
           'conditions': [
             ['node_shared != "true"', {
               'MSVC_runtimeType': 0    # MultiThreaded (/MT)
             }, {
               'MSVC_runtimeType': 2   # MultiThreadedDLL (/MD)
             }],
+            ['llvm_version=="0.0"', {
+              'lto': ' -flto=4 -fuse-linker-plugin -ffat-lto-objects ', # GCC
+            }, {
+              'lto': ' -flto ', # Clang
+            }],
           ],
         },
         'cflags': [ '-O3' ],
         'conditions': [
+          ['enable_lto=="true"', {
+            'cflags': ['<(lto)'],
+            'ldflags': ['<(lto)'],
+            'xcode_settings': {
+              'LLVM_LTO': 'YES',
+            },
+          }],
           ['OS=="linux"', {
             'conditions': [
               ['node_section_ordering_info!=""', {
@@ -206,10 +217,6 @@
                 'cflags': ['<(pgo_use)'],
                 'ldflags': ['<(pgo_use)'],
               },],
-              ['enable_lto=="true"', {
-                'cflags': ['<(lto)'],
-                'ldflags': ['<(lto)'],
-              },],
             ],
           },],
           ['OS == "android"', {

configure.py

@@ -173,7 +173,7 @@
     dest="enable_lto",
     default=None,
     help="Enable compiling with lto of a binary. This feature is only available "
-         "on linux with gcc and g++ 5.4.1 or newer.")
+         "with gcc 5.4.1+ or clang 3.9.1+.")
 
 parser.add_argument("--link-module",
     action="append",
@@ -952,6 +952,7 @@ def get_gas_version(cc):
 # quite prepared to go that far yet.
 def check_compiler(o):
   if sys.platform == 'win32':
+    o['variables']['llvm_version'] = '0.0'
     if not options.openssl_no_asm and options.dest_cpu in ('x86', 'x64'):
       nasm_version = get_nasm_version('nasm')
       o['variables']['nasm_version'] = nasm_version
@@ -1131,12 +1132,19 @@ def configure_mips(o, target_arch):
   host_byteorder = 'little' if target_arch in ('mipsel', 'mips64el') else 'big'
   o['variables']['v8_host_byteorder'] = host_byteorder
 
+def clang_version_ge(version_checked):
+  for compiler in [(CC, 'c'), (CXX, 'c++')]:
+    ok, is_clang, clang_version, gcc_version = \
+      try_check_compiler(compiler[0], compiler[1])
+    if is_clang and clang_version >= version_checked:
+      return True
+  return False
 
 def gcc_version_ge(version_checked):
   for compiler in [(CC, 'c'), (CXX, 'c++')]:
-    ok, is_clang, clang_version, compiler_version = \
+    ok, is_clang, clang_version, gcc_version = \
       try_check_compiler(compiler[0], compiler[1])
-    if is_clang or compiler_version < version_checked:
+    if is_clang or gcc_version < version_checked:
       return False
   return True
 
@@ -1217,18 +1225,19 @@ def configure_node(o):
   o['variables']['enable_pgo_generate'] = b(options.enable_pgo_generate)
   o['variables']['enable_pgo_use']      = b(options.enable_pgo_use)
 
-  if flavor != 'linux' and (options.enable_lto):
+  if flavor == 'win' and (options.enable_lto):
     raise Exception(
-      'The lto option is supported only on linux.')
-
-  if flavor == 'linux':
-    if options.enable_lto:
-      version_checked = (5, 4, 1)
-      if not gcc_version_ge(version_checked):
-        version_checked_str = ".".join(map(str, version_checked))
-        raise Exception(
-          'The option --enable-lto is supported for gcc and gxx %s'
-          ' or newer only.' % (version_checked_str))
+      'Use Link Time Code Generation instead.')
+
+  if options.enable_lto:
+    gcc_version_checked = (5, 4, 1)
+    clang_version_checked = (3, 9, 1)
+    if not gcc_version_ge(gcc_version_checked) and not clang_version_ge(clang_version_checked):
+      gcc_version_checked_str = ".".join(map(str, gcc_version_checked))
+      clang_version_checked_str = ".".join(map(str, clang_version_checked))
+      raise Exception(
+        'The option --enable-lto is supported for gcc %s+'
+        'or clang %s+ only.' % (gcc_version_checked_str, clang_version_checked_str))
 
   o['variables']['enable_lto'] = b(options.enable_lto)