suggest use of EMTERPRETIFY_FILE when emterpreter bitcode is large

tests/test_other.py

@@ -5166,3 +5166,16 @@ main(int argc, char **argv)
     out, err = Popen([PYTHON, EMCC, path_from_root('tests', 'hello_libcxx.cpp')], stderr=PIPE).communicate()
     assert err == '', err
 
+  def test_emterpreter_file_suggestion(self):
+    for linkable in [0, 1]:
+      for to_file in [0, 1]:
+        self.clear()
+        cmd = [PYTHON, EMCC, '-s', 'EMTERPRETIFY=1', path_from_root('tests', 'hello_libcxx.cpp'), '-s', 'LINKABLE=' + str(linkable), '-O1', '-s', 'USE_ZLIB=1']
+        if to_file:
+          cmd += ['-s', 'EMTERPRETIFY_FILE="code.dat"']
+        print cmd
+        stdout, stderr = Popen(cmd, stderr=PIPE).communicate()
+        need_warning = linkable and not to_file
+        assert ('''warning: emterpreter bytecode is fairly large''' in stderr) == need_warning, stderr
+        assert ('''It is recommended to use  -s EMTERPRETIFY_FILE=..''' in stderr) == need_warning, stderr
+

tools/emterpretify.py

@@ -1044,6 +1044,9 @@ __ATPRERUN__.push(function() {
 ''' % (len(all_code), all_code[0], all_code[1], all_code[2], all_code[3], len(relocations), relocations[0])]
 
   else:
+    if len(all_code) > 1024*1024:
+      shared.logging.warning('warning: emterpreter bytecode is fairly large, %.2f MB. It is recommended to use  -s EMTERPRETIFY_FILE=..  so that it is saved as a binary file, instead of the default behavior which is to embed it as text (as text, it can cause very slow compile and startup times)' % (len(all_code) / (1024*1024.)))
+
     CHUNK_SIZE = 10240
 
     i = 0