[infra] Cleanup buildfile generation scripts a bit

tools/gn.py

 #!/usr/bin/env python
 # Copyright 2016 The Dart project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import argparse
 import multiprocessing
 import os
 import shutil
 import subprocess
@@ skipping 93 matching lines @@
 # Where string_map is formatted as X1=Y1,X2=Y2 etc.
 # If key is X1, returns Y1.
 def ParseStringMap(key, string_map):
   for m in string_map.split(','):
     l = m.split('=')
     if l[0] == key:
       return l[1]
   return None
 
 
+def UseSanitizer(args):
+  return args.asan or args.msan or args.tsan
+
+
+def DontUseClang(args, target_os, host_cpu, target_cpu):
+  # We don't have clang on Windows.
+  return (target_os == 'win'
+         # TODO(zra): Experiment with using clang for the arm cross-builds.
+         or (target_os == 'linux'
+             and (target_cpu.startswith('arm') or
+                  target_cpu.startswith('mips'))
+         # TODO(zra): Only use clang when a sanitizer build is specified until
+         # clang bugs in inline assembly for ia32 are fixed.

[rmacnak, 2017/05/08 18:04:53]

Consider:
inline assembly -> tcmalloc's inline assembly

[zra, 2017/05/08 18:37:10]

Done.

+         or (target_os == 'linux')
+             and host_cpu == 'x86'
+             and not UseSanitizer(args)))
+
+
 def ToGnArgs(args, mode, arch, target_os):
   gn_args = {}
 
   host_os = HostOsForGn(HOST_OS)
   if target_os == 'host':
     gn_args['target_os'] = host_os
   else:
     gn_args['target_os'] = target_os
 
   gn_args['dart_target_arch'] = arch
   gn_args['target_cpu'] = TargetCpuForArch(arch, target_os)
   gn_args['host_cpu'] = HostCpuForArch(arch)
 
   # See: runtime/observatory/BUILD.gn.
   # This allows the standalone build of the observatory to fall back on
   # dart_bootstrap if the prebuilt SDK doesn't work.
   gn_args['dart_host_pub_exe'] = ""
 
   # We only want the fallback root certs in the standalone VM on
   # Linux and Windows.
   if gn_args['target_os'] in ['linux', 'win']:
     gn_args['dart_use_fallback_root_certificates'] = True
 
   gn_args['dart_zlib_path'] = "//runtime/bin/zlib"
 
   # Use tcmalloc only when targeting Linux and when not using ASAN.
   gn_args['dart_use_tcmalloc'] = ((gn_args['target_os'] == 'linux')
-                                  and not args.asan
-                                  and not args.msan
-                                  and not args.tsan)
+                                  and not UseSanitizer(args))
 
   if gn_args['target_os'] == 'linux':
     if gn_args['target_cpu'] == 'arm':
       # Force -mfloat-abi=hard and -mfpu=neon for arm on Linux as we're
       # specifying a gnueabihf compiler in //build/toolchain/linux BUILD.gn.
       gn_args['arm_arch'] = 'armv7'
       gn_args['arm_float_abi'] = 'hard'
       gn_args['arm_use_neon'] = True
     elif gn_args['target_cpu'] == 'armv6':
       raise Exception("GN support for armv6 unimplemented")
     elif gn_args['target_cpu'] == 'armv5te':
       raise Exception("GN support for armv5te unimplemented")
 
   gn_args['is_debug'] = mode == 'debug'
   gn_args['is_release'] = mode == 'release'
   gn_args['is_product'] = mode == 'product'
   gn_args['dart_debug'] = mode == 'debug'
 
   # This setting is only meaningful for Flutter. Standalone builds of the VM
   # should leave this set to 'develop', which causes the build to defer to
   # 'is_debug', 'is_release' and 'is_product'.
   gn_args['dart_runtime_mode'] = 'develop'
 
-  # TODO(zra): Investigate using clang with these configurations.
-  # Clang compiles tcmalloc's inline assembly for ia32 on Linux wrong, so we
-  # don't use clang in that configuration. Thus, we use gcc for ia32 *unless*
-  # a clang-based sanitizer is specified.
-  has_clang = (host_os != 'win'
-               and not gn_args['target_cpu'].startswith('mips')
-               and not ((gn_args['target_os'] == 'linux') and
-                        (gn_args['target_cpu'] == 'arm64'))
-               and not ((gn_args['target_os'] == 'linux')
-                        and (gn_args['host_cpu'] == 'x86')
-                        and not args.asan
-                        and not args.msan
-                        and not args.tsan))  # Use clang for sanitizer builds.
-  gn_args['is_clang'] = args.clang and has_clang
+  dont_use_clang = DontUseClang(args, gn_args['target_os'],
+                                      gn_args['host_cpu'],
+                                      gn_args['target_cpu'])
+  gn_args['is_clang'] = args.clang and not dont_use_clang
 
   gn_args['is_asan'] = args.asan and gn_args['is_clang']
   gn_args['is_msan'] = args.msan and gn_args['is_clang']
   gn_args['is_tsan'] = args.tsan and gn_args['is_clang']
 
   # Setup the user-defined sysroot.
   if gn_args['target_os'] == 'linux' and args.wheezy:
     gn_args['dart_use_wheezy_sysroot'] = True
   else:
     sysroot = TargetSysroot(args)
@@ skipping 236 matching lines @@
       return 1
 
   endtime = time.time()
   if args.verbose:
     print ("GN Time: %.3f seconds" % (endtime - starttime))
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(Main(sys.argv))