path: root/emscripten.py

#!/usr/bin/env python2

'''
You should normally never use this! Use emcc instead.

This is a small wrapper script around the core JS compiler. This calls that
compiler with the settings given to it. It can also read data from C/C++
header files (so that the JS compiler can see the constants in those
headers, for the libc implementation in JS).
'''

import os, sys, json, optparse, subprocess, re, time, multiprocessing

if not os.environ.get('EMSCRIPTEN_SUPPRESS_USAGE_WARNING'):
  print >> sys.stderr, '''
==============================================================
WARNING: You should normally never use this! Use emcc instead.
==============================================================
  '''

from tools import shared

DEBUG = os.environ.get('EMCC_DEBUG')
if DEBUG == "0":
  DEBUG = None
DEBUG_CACHE = DEBUG and "cache" in DEBUG

__rootpath__ = os.path.abspath(os.path.dirname(__file__))
def path_from_root(*pathelems):
  """Returns the absolute path for which the given path elements are
  relative to the emscripten root.
  """
  return os.path.join(__rootpath__, *pathelems)

configuration = shared.Configuration(environ=os.environ)
temp_files = shared.make_temp_files()

compiler_engine = None
jcache = False

def scan(ll, settings):
  # blockaddress(@main, %23)
  blockaddrs = []
  for blockaddr in re.findall('blockaddress\([^)]*\)', ll):
    b = blockaddr.split('(')[1][:-1].split(', ')
    blockaddrs.append(b)
  if len(blockaddrs) > 0:
    settings['NECESSARY_BLOCKADDRS'] = blockaddrs

NUM_CHUNKS_PER_CORE = 1.25
MIN_CHUNK_SIZE = 1024*1024
MAX_CHUNK_SIZE = float(os.environ.get('EMSCRIPT_MAX_CHUNK_SIZE') or 'inf') # configuring this is just for debugging purposes

def process_funcs(args):
  i, funcs, meta, settings_file, compiler, forwarded_file, libraries = args
  ll = ''.join(funcs) + '\n' + meta
  funcs_file = temp_files.get('.func_%d.ll' % i).name
  open(funcs_file, 'w').write(ll)
  out = shared.run_js(compiler, compiler_engine, [settings_file, funcs_file, 'funcs', forwarded_file] + libraries, stdout=subprocess.PIPE, cwd=path_from_root('src'))
  shared.try_delete(funcs_file)
  return out

def emscript(infile, settings, outfile, libraries=[]):
  """Runs the emscripten LLVM-to-JS compiler. We parallelize as much as possible

  Args:
    infile: The path to the input LLVM assembly file.
    settings: JSON-formatted settings that override the values
      defined in src/settings.js.
    outfile: The file where the output is written.
  """

  compiler = path_from_root('src', 'compiler.js')

  # Parallelization: We run 3 phases:
  #   1 aka 'pre'  : Process types and metadata and so forth, and generate the preamble.
  #   2 aka 'funcs': Process functions. We can parallelize this, working on each function independently.
  #   3 aka 'post' : Process globals, generate postamble and finishing touches.

  if DEBUG: print >> sys.stderr, 'emscript: ll=>js'

  if jcache: shared.JCache.ensure()

  # Pre-scan ll and alter settings as necessary
  if DEBUG: t = time.time()
  ll = open(infile).read()
  scan(ll, settings)
  total_ll_size = len(ll)
  ll = None # allow collection
  if DEBUG: print >> sys.stderr, '  emscript: scan took %s seconds' % (time.time() - t)

  # Split input into the relevant parts for each phase
  pre = []
  funcs = [] # split up functions here, for parallelism later
  func_idents = []
  meta = [] # needed by each function XXX

  if DEBUG: t = time.time()
  in_func = False
  ll_lines = open(infile).readlines()
  for line in ll_lines:
    if in_func:
      funcs[-1][1].append(line)
      if line.startswith('}'):
        in_func = False
        funcs[-1] = (funcs[-1][0], ''.join(funcs[-1][1]))
        pre.append(line) # pre needs it to, so we know about all implemented functions
    else:
      if line.startswith(';'): continue
      if line.startswith('define '):
        in_func = True
        funcs.append((line, [line])) # use the entire line as the identifier
        pre.append(line) # pre needs it to, so we know about all implemented functions
      elif line.find(' = type { ') > 0:
        pre.append(line) # type
      elif line.startswith('!'):
        if line.startswith('!llvm.module'): continue # we can ignore that
        meta.append(line) # metadata
      else:
        pre.append(line) # pre needs it so we know about globals in pre and funcs. So emit globals there
  ll_lines = None
  meta = ''.join(meta)
  if DEBUG and len(meta) > 1024*1024: print >> sys.stderr, 'emscript warning: large amounts of metadata, will slow things down'
  if DEBUG: print >> sys.stderr, '  emscript: split took %s seconds' % (time.time() - t)

  #if DEBUG:
  #  print >> sys.stderr, '========= pre ================\n'
  #  print >> sys.stderr, ''.join(pre)
  #  print >> sys.stderr, '========== funcs ===============\n'
  #  for func in funcs:
  #    print >> sys.stderr, '\n// ===\n\n', ''.join(func)
  #  print >> sys.stderr, '=========================\n'

  # Save settings to a file to work around v8 issue 1579
  settings_file = temp_files.get('.txt').name
  def save_settings():
    global settings_text
    settings_text = json.dumps(settings, sort_keys=True)
    s = open(settings_file, 'w')
    s.write(settings_text)
    s.close()
  save_settings()

  # Phase 1 - pre
  if DEBUG: t = time.time()
  pre_file = temp_files.get('.pre.ll').name
  pre_input = ''.join(pre) + '\n' + meta
  out = None
  if jcache:
    keys = [pre_input, settings_text, ','.join(libraries)]
    shortkey = shared.JCache.get_shortkey(keys)
    if DEBUG_CACHE: print >>sys.stderr, 'shortkey', shortkey

    out = shared.JCache.get(shortkey, keys)

    if DEBUG_CACHE and not out:
      dfpath = os.path.join(shared.TEMP_DIR, "ems_" + shortkey)
      dfp = open(dfpath, 'w')
      dfp.write(pre_input);
      dfp.write("\n\n========================== settings_text\n\n");
      dfp.write(settings_text);
      dfp.write("\n\n========================== libraries\n\n");
      dfp.write("\n".join(libraries))
      dfp.close()
      print >>sys.stderr, '  cache miss, key data dumped to %s' % dfpath

    if out and DEBUG: print >> sys.stderr, '  loading pre from jcache'
  if not out:
    open(pre_file, 'w').write(pre_input)
    out = shared.run_js(compiler, shared.COMPILER_ENGINE, [settings_file, pre_file, 'pre'] + libraries, stdout=subprocess.PIPE, cwd=path_from_root('src'))
    if jcache:
      if DEBUG: print >> sys.stderr, '  saving pre to jcache'
      shared.JCache.set(shortkey, keys, out)
  pre, forwarded_data = out.split('//FORWARDED_DATA:')
  forwarded_file = temp_files.get('.json').name
  open(forwarded_file, 'w').write(forwarded_data)
  if DEBUG: print >> sys.stderr, '  emscript: phase 1 took %s seconds' % (time.time() - t)

  # Phase 2 - func

  cores = int(os.environ.get('EMCC_CORES') or multiprocessing.cpu_count())
  assert cores >= 1
  if cores > 1:
    intended_num_chunks = int(round(cores * NUM_CHUNKS_PER_CORE))
    chunk_size = max(MIN_CHUNK_SIZE, total_ll_size / intended_num_chunks)
    chunk_size += 3*len(meta) + len(forwarded_data)/3 # keep ratio of lots of function code to meta (expensive to process, and done in each parallel task) and forwarded data (less expensive but potentially significant)
    chunk_size = min(MAX_CHUNK_SIZE, chunk_size)
  else:
    chunk_size = MAX_CHUNK_SIZE # if 1 core, just use the max chunk size

  if DEBUG: t = time.time()
  forwarded_json = json.loads(forwarded_data)
  indexed_functions = set()
  if settings.get('ASM_JS'):
    settings['EXPORTED_FUNCTIONS'] = forwarded_json['EXPORTED_FUNCTIONS']
    save_settings()

  chunks = shared.JCache.chunkify(funcs, chunk_size, 'emscript_files' if jcache else None)

  if jcache:
    # load chunks from cache where we can # TODO: ignore small chunks
    cached_outputs = []
    def load_from_cache(chunk):
      keys = [settings_text, forwarded_data, chunk]
      shortkey = shared.JCache.get_shortkey(keys) # TODO: share shortkeys with later code
      out = shared.JCache.get(shortkey, keys) # this is relatively expensive (pickling?)
      if out:
        cached_outputs.append(out)
        return False
      return True
    chunks = filter(load_from_cache, chunks)
    if len(cached_outputs) > 0:
      if out and DEBUG: print >> sys.stderr, '  loading %d funcchunks from jcache' % len(cached_outputs)
    else:
      cached_outputs = []

  # TODO: minimize size of forwarded data from funcs to what we actually need

  if cores == 1 and total_ll_size < MAX_CHUNK_SIZE: assert len(chunks) == 1, 'no point in splitting up without multiple cores'

  if len(chunks) > 0:
    if DEBUG: print >> sys.stderr, '  emscript: phase 2 working on %d chunks %s (intended chunk size: %.2f MB, meta: %.2f MB, forwarded: %.2f MB, total: %.2f MB)' % (len(chunks), ('using %d cores' % cores) if len(chunks) > 1 else '', chunk_size/(1024*1024.), len(meta)/(1024*1024.), len(forwarded_data)/(1024*1024.), total_ll_size/(1024*1024.))

    commands = [(i, chunks[i], meta, settings_file, compiler, forwarded_file, libraries) for i in range(len(chunks))]

    if len(chunks) > 1:
      pool = multiprocessing.Pool(processes=cores)
      outputs = pool.map(process_funcs, commands, chunksize=1)
    elif len(chunks) == 1:
      outputs = [process_funcs(commands[0])]
  else:
    outputs = []

  if jcache:
    # save chunks to cache
    for i in range(len(chunks)):
      chunk = chunks[i]
      keys = [settings_text, forwarded_data, chunk]
      shortkey = shared.JCache.get_shortkey(keys)
      shared.JCache.set(shortkey, keys, outputs[i])
    if out and DEBUG and len(chunks) > 0: print >> sys.stderr, '  saving %d funcchunks to jcache' % len(chunks)

  if jcache: outputs += cached_outputs # TODO: preserve order

  outputs = [output.split('//FORWARDED_DATA:') for output in outputs]
  for output in outputs:
    assert len(output) == 2, 'Did not receive forwarded data in an output - process failed? We only got: ' + output[0]

  if DEBUG: print >> sys.stderr, '  emscript: phase 2 took %s seconds' % (time.time() - t)
  if DEBUG: t = time.time()

  # merge forwarded data
  if settings.get('ASM_JS'):
    all_exported_functions = set(settings['EXPORTED_FUNCTIONS']) # both asm.js and otherwise
    for additional_export in settings['DEFAULT_LIBRARY_FUNCS_TO_INCLUDE']: # additional functions to export from asm, if they are implemented
      all_exported_functions.add('_' + additional_export)
    exported_implemented_functions = set()
  for func_js, curr_forwarded_data in outputs:
    curr_forwarded_json = json.loads(curr_forwarded_data)
    forwarded_json['Types']['preciseI64MathUsed'] = forwarded_json['Types']['preciseI64MathUsed'] or curr_forwarded_json['Types']['preciseI64MathUsed']
    for key, value in curr_forwarded_json['Functions']['blockAddresses'].iteritems():
      forwarded_json['Functions']['blockAddresses'][key] = value
    for key in curr_forwarded_json['Functions']['indexedFunctions'].iterkeys():
      indexed_functions.add(key)
    if settings.get('ASM_JS'):
      for key in curr_forwarded_json['Functions']['implementedFunctions'].iterkeys():
        if key in all_exported_functions: exported_implemented_functions.add(key)
    for key, value in curr_forwarded_json['Functions']['unimplementedFunctions'].iteritems():
      forwarded_json['Functions']['unimplementedFunctions'][key] = value

  if settings.get('ASM_JS'):
    parts = pre.split('// ASM_LIBRARY FUNCTIONS\n')
    if len(parts) > 1:
      pre = parts[0]
      outputs.append([parts[1]])
  funcs_js = ''.join([output[0] for output in outputs])

  outputs = None
  if DEBUG: print >> sys.stderr, '  emscript: phase 2b took %s seconds' % (time.time() - t)
  if DEBUG: t = time.time()

  # calculations on merged forwarded data
  forwarded_json['Functions']['indexedFunctions'] = {}
  i = 2
  for indexed in indexed_functions:
    #print >> sys.stderr, 'indaxx', indexed, i
    forwarded_json['Functions']['indexedFunctions'][indexed] = i # make sure not to modify this python object later - we use it in indexize
    i += 2
  forwarded_json['Functions']['nextIndex'] = i

  indexing = forwarded_json['Functions']['indexedFunctions']
  def indexize(js):
    return re.sub(r"'{{ FI_([\w\d_$]+) }}'", lambda m: str(indexing.get(m.groups(0)[0]) or 0), js)

  blockaddrs = forwarded_json['Functions']['blockAddresses']
  def blockaddrsize(js):
    return re.sub(r'{{{ BA_([\w\d_$]+)\|([\w\d_$]+) }}}', lambda m: str(blockaddrs[m.groups(0)[0]][m.groups(0)[1]]), js)

  #if DEBUG: outfile.write('// pre\n')
  outfile.write(blockaddrsize(indexize(pre)))
  pre = None

  #if DEBUG: outfile.write('// funcs\n')

  # forward
  forwarded_data = json.dumps(forwarded_json)
  forwarded_file = temp_files.get('.2.json').name
  open(forwarded_file, 'w').write(indexize(forwarded_data))
  if DEBUG: print >> sys.stderr, '  emscript: phase 2c took %s seconds' % (time.time() - t)

  # Phase 3 - post
  if DEBUG: t = time.time()
  post_file = temp_files.get('.post.ll').name
  open(post_file, 'w').write('\n') # no input, just processing of forwarded data
  out = shared.run_js(compiler, shared.COMPILER_ENGINE, [settings_file, post_file, 'post', forwarded_file] + libraries, stdout=subprocess.PIPE, cwd=path_from_root('src'))
  post, last_forwarded_data = out.split('//FORWARDED_DATA:') # if this fails, perhaps the process failed prior to printing forwarded data?
  last_forwarded_json = json.loads(last_forwarded_data)

  if settings.get('ASM_JS'):
    simple = os.environ.get('EMCC_SIMPLE_ASM')
    class Counter:
      i = 0
    pre_tables = last_forwarded_json['Functions']['tables']['pre']
    del last_forwarded_json['Functions']['tables']['pre']

    # Find function table calls without function tables generated for them
    for use in set(re.findall(r'{{{ FTM_[\w\d_$]+ }}}', funcs_js)):
      sig = use[8:len(use)-4]
      if sig not in last_forwarded_json['Functions']['tables']:
        if DEBUG: print >> sys.stderr, 'add empty function table', sig
        last_forwarded_json['Functions']['tables'][sig] = 'var FUNCTION_TABLE_' + sig + ' = [0,0];\n'

    def make_table(sig, raw):
      i = Counter.i
      Counter.i += 1
      bad = 'b' + str(i)
      params = ','.join(['p%d' % p for p in range(len(sig)-1)])
      coercions = ';'.join(['p%d = %sp%d%s' % (p, '+' if sig[p+1] != 'i' else '', p, '' if sig[p+1] != 'i' else '|0') for p in range(len(sig)-1)]) + ';'
      ret = '' if sig[0] == 'v' else ('return %s0' % ('+' if sig[0] != 'i' else ''))
      return ('function %s(%s) { %s abort(%d); %s };' % (bad, params, coercions, i, ret), raw.replace('[0,', '[' + bad + ',').replace(',0,', ',' + bad + ',').replace(',0,', ',' + bad + ',').replace(',0]', ',' + bad + ']').replace(',0]', ',' + bad + ']').replace(',0\n', ',' + bad + '\n'))
    infos = [make_table(sig, raw) for sig, raw in last_forwarded_json['Functions']['tables'].iteritems()]
    function_tables_defs = '\n'.join([info[0] for info in infos] + [info[1] for info in infos])

    asm_setup = ''
    maths = ['Math.' + func for func in ['floor', 'abs', 'sqrt', 'pow', 'cos', 'sin', 'tan', 'acos', 'asin', 'atan', 'atan2', 'exp', 'log', 'ceil', 'imul']]
    fundamentals = ['Math', 'Int8Array', 'Int16Array', 'Int32Array', 'Uint8Array', 'Uint16Array', 'Uint32Array', 'Float32Array', 'Float64Array']
    math_envs = ['Runtime.bitshift64', 'Math.min'] # TODO: move min to maths
    asm_setup += '\n'.join(['var %s = %s;' % (f.replace('.', '_'), f) for f in math_envs])
    basic_funcs = ['abort', 'assert', 'asmPrintInt', 'asmPrintFloat', 'copyTempDouble', 'copyTempFloat'] + [m.replace('.', '_') for m in math_envs]
    if settings['SAFE_HEAP']: basic_funcs += ['SAFE_HEAP_LOAD', 'SAFE_HEAP_STORE', 'SAFE_HEAP_CLEAR']
    if settings['CHECK_HEAP_ALIGN']: basic_funcs += ['CHECK_ALIGN_2', 'CHECK_ALIGN_4', 'CHECK_ALIGN_8']
    basic_vars = ['STACKTOP', 'STACK_MAX', 'tempDoublePtr', 'ABORT']
    basic_float_vars = ['NaN', 'Infinity']
    if forwarded_json['Types']['preciseI64MathUsed']:
      basic_funcs += ['i64Math_' + op for op in ['add', 'subtract', 'multiply', 'divide', 'modulo']]
      asm_setup += '''
var i64Math_add = function(a, b, c, d) { i64Math.add(a, b, c, d) };
var i64Math_subtract = function(a, b, c, d) { i64Math.subtract(a, b, c, d) };
var i64Math_multiply = function(a, b, c, d) { i64Math.multiply(a, b, c, d) };
var i64Math_divide = function(a, b, c, d, e) { i64Math.divide(a, b, c, d, e) };
var i64Math_modulo = function(a, b, c, d, e) { i64Math.modulo(a, b, c, d, e) };
'''
    asm_runtime_funcs = ['stackAlloc', 'stackSave', 'stackRestore', 'setThrew'] + ['setTempRet%d' % i for i in range(10)]
    # function tables
    def asm_coerce(value, sig):
      if sig == 'v': return value
      return ('+' if sig != 'i' else '') + value + ('|0' if sig == 'i' else '')
        
    function_tables = ['dynCall_' + table for table in last_forwarded_json['Functions']['tables']]
    function_tables_impls = []
    for sig in last_forwarded_json['Functions']['tables'].iterkeys():
      args = ','.join(['a' + str(i) for i in range(1, len(sig))])
      arg_coercions = ' '.join(['a' + str(i) + '=' + asm_coerce('a' + str(i), sig[i]) + ';' for i in range(1, len(sig))])
      coerced_args = ','.join([asm_coerce('a' + str(i), sig[i]) for i in range(1, len(sig))])
      ret = ('return ' if sig[0] != 'v' else '') + asm_coerce('FUNCTION_TABLE_%s[index&{{{ FTM_%s }}}](%s)' % (sig, sig, coerced_args), sig[0])
      function_tables_impls.append('''
  function dynCall_%s(index%s%s) {
    index = index|0;
    %s
    %s;
  }
''' % (sig, ',' if len(sig) > 1 else '', args, arg_coercions, ret))

    # calculate exports
    exported_implemented_functions = list(exported_implemented_functions)
    exports = []
    if not simple:
      for export in exported_implemented_functions + asm_runtime_funcs + function_tables:
        exports.append("%s: %s" % (export, export))
      exports = '{ ' + ', '.join(exports) + ' }'
    else:
      exports = '_main'
    # calculate globals
    try:
      del forwarded_json['Variables']['globals']['_llvm_global_ctors'] # not a true variable
    except:
      pass
    # If no named globals, only need externals
    global_vars = map(lambda g: g['name'], filter(lambda g: settings['NAMED_GLOBALS'] or g.get('external') or g.get('unIndexable'), forwarded_json['Variables']['globals'].values()))
    global_funcs = ['_' + x for x in forwarded_json['Functions']['libraryFunctions'].keys()]
    def math_fix(g):
      return g if not g.startswith('Math_') else g.split('_')[1];
    asm_global_funcs = ''.join(['  var ' + g.replace('.', '_') + '=global.' + g + ';\n' for g in maths]) + \
                       ''.join(['  var ' + g + '=env.' + math_fix(g) + ';\n' for g in basic_funcs + global_funcs])
    asm_global_vars = ''.join(['  var ' + g + '=env.' + g + '|0;\n' for g in basic_vars + global_vars]) + \
                      ''.join(['  var ' + g + '=+env.' + g + ';\n' for g in basic_float_vars])
    # sent data
    the_global = '{ ' + ', '.join([math_fix(s) + ': ' + s for s in fundamentals]) + ' }'
    sending = '{ ' + ', '.join([math_fix(s) + ': ' + s for s in basic_funcs + global_funcs + basic_vars + basic_float_vars + global_vars]) + ' }'
    # received
    if not simple:
      receiving = ';\n'.join(['var ' + s + ' = Module["' + s + '"] = asm.' + s for s in exported_implemented_functions + function_tables])
    else:
      receiving = 'var _main = Module["_main"] = asm;'
    # finalize
    funcs_js = '''
%s
function asmPrintInt(x, y) {
  Module.print('int ' + x + ',' + y);// + ' ' + new Error().stack);
}
function asmPrintFloat(x, y) {
  Module.print('float ' + x + ',' + y);// + ' ' + new Error().stack);
}
var asm = (function(global, env, buffer) {
  'use asm';
  var HEAP8 = new global.Int8Array(buffer);
  var HEAP16 = new global.Int16Array(buffer);
  var HEAP32 = new global.Int32Array(buffer);
  var HEAPU8 = new global.Uint8Array(buffer);
  var HEAPU16 = new global.Uint16Array(buffer);
  var HEAPU32 = new global.Uint32Array(buffer);
  var HEAPF32 = new global.Float32Array(buffer);
  var HEAPF64 = new global.Float64Array(buffer);
''' % (asm_setup,) + '\n' + asm_global_vars + '''
  var __THREW__ = 0;
  var undef = 0;
  var tempInt = 0, tempBigInt = 0, tempBigIntP = 0, tempBigIntS = 0, tempBigIntR = 0.0, tempBigIntI = 0, tempBigIntD = 0, tempValue = 0, tempDouble = 0.0;
''' + ''.join(['''
  var tempRet%d = 0;''' % i for i in range(10)]) + '\n' + asm_global_funcs + '''
  function stackAlloc(size) {
    size = size|0;
    var ret = 0;
    ret = STACKTOP;
    STACKTOP = (STACKTOP + size)|0;
    STACKTOP = ((STACKTOP + 3)>>2)<<2;
    return ret|0;
  }
  function stackSave() {
    return STACKTOP|0;
  }
  function stackRestore(top) {
    top = top|0;
    STACKTOP = top;
  }
  function setThrew(threw) {
    threw = threw|0;
    __THREW__ = threw;
  }
''' + ''.join(['''
  function setTempRet%d(value) {
    value = value|0;
    tempRet%d = value;
  }
''' % (i, i) for i in range(10)]) + funcs_js + '''

  %s

  return %s;
})(%s, %s, buffer);
%s;
Runtime.stackAlloc = function(size) { return asm.stackAlloc(size) };
Runtime.stackSave = function() { return asm.stackSave() };
Runtime.stackRestore = function(top) { asm.stackRestore(top) };
''' % (pre_tables + '\n'.join(function_tables_impls) + '\n' + function_tables_defs.replace('\n', '\n  '), exports, the_global, sending, receiving)

    # Set function table masks
    def function_table_maskize(js):
      masks = {}
      default = None
      for sig, table in last_forwarded_json['Functions']['tables'].iteritems():
        masks[sig] = str(table.count(','))
        default = sig
      def fix(m):
        sig = m.groups(0)[0]
        return masks[sig]
      return re.sub(r'{{{ FTM_([\w\d_$]+) }}}', lambda m: fix(m), js) # masks[m.groups(0)[0]]
    funcs_js = function_table_maskize(funcs_js)
  else:
    function_tables_defs = '\n'.join([table for table in last_forwarded_json['Functions']['tables'].itervalues()])
    outfile.write(function_tables_defs)
  outfile.write(blockaddrsize(indexize(funcs_js)))
  funcs_js = None

  outfile.write(indexize(post))
  if DEBUG: print >> sys.stderr, '  emscript: phase 3 took %s seconds' % (time.time() - t)

  outfile.close()


def main(args):
  # Prepare settings for serialization to JSON.
  settings = {}
  for setting in args.settings:
    name, value = setting.strip().split('=', 1)
    settings[name] = json.loads(value)

  # Add header defines to settings
  defines = {}
  include_root = path_from_root('system', 'include')
  headers = args.headers[0].split(',') if len(args.headers) > 0 else []
  seen_headers = set()
  while len(headers) > 0:
    header = headers.pop(0)
    if not os.path.isabs(header):
      header = os.path.join(include_root, header)
    seen_headers.add(header)
    for line in open(header, 'r'):
      line = line.replace('\t', ' ')
      m = re.match('^ *# *define +(?P<name>[-\w_.]+) +\(?(?P<value>[-\w_.|]+)\)?.*', line)
      if not m:
        # Catch enum defines of a very limited sort
        m = re.match('^ +(?P<name>[A-Z_\d]+) += +(?P<value>\d+).*', line)
      if m:
        if m.group('name') != m.group('value'):
          defines[m.group('name')] = m.group('value')
        #else:
        #  print 'Warning: %s #defined to itself' % m.group('name') # XXX this can happen if we are set to be equal to an enum (with the same name)
      m = re.match('^ *# *include *["<](?P<name>[\w_.-/]+)[">].*', line)
      if m:
        # Find this file
        found = False
        for w in [w for w in os.walk(include_root)]:
          for f in w[2]:
            curr = os.path.join(w[0], f)
            if curr.endswith(m.group('name')) and curr not in seen_headers:
              headers.append(curr)
              found = True
              break
          if found: break
        #assert found, 'Could not find header: ' + m.group('name')
  if len(defines) > 0:
    def lookup(value):
      try:
        while not unicode(value).isnumeric():
          value = defines[value]
        return value
      except:
        pass
      try: # 0x300 etc.
        value = eval(value)
        return value
      except:
        pass
      try: # CONST1|CONST2
        parts = map(lookup, value.split('|'))
        value = reduce(lambda a, b: a|b, map(eval, parts))
        return value
      except:
        pass
      return None
    for key, value in defines.items():
      value = lookup(value)
      if value is not None:
        defines[key] = str(value)
      else:
        del defines[key]
    #print >> sys.stderr, 'new defs:', str(defines).replace(',', ',\n  '), '\n\n'
    settings.setdefault('C_DEFINES', {}).update(defines)

  # libraries
  libraries = args.libraries[0].split(',') if len(args.libraries) > 0 else []

  # Compile the assembly to Javascript.
  if settings.get('RELOOP'): shared.Building.ensure_relooper()

  emscript(args.infile, settings, args.outfile, libraries)

def _main():
  parser = optparse.OptionParser(
      usage='usage: %prog [-h] [-H HEADERS] [-o OUTFILE] [-c COMPILER_ENGINE] [-s FOO=BAR]* infile',
      description=('You should normally never use this! Use emcc instead. '
                   'This is a wrapper around the JS compiler, converting .ll to .js.'),
      epilog='')
  parser.add_option('-H', '--headers',
                    default=[],
                    action='append',
                    help='System headers (comma separated) whose #defines should be exposed to the compiled code.')
  parser.add_option('-L', '--libraries',
                    default=[],
                    action='append',
                    help='Library files (comma separated) to use in addition to those in emscripten src/library_*.')
  parser.add_option('-o', '--outfile',
                    default=sys.stdout,
                    help='Where to write the output; defaults to stdout.')
  parser.add_option('-c', '--compiler',
                    default=shared.COMPILER_ENGINE,
                    help='Which JS engine to use to run the compiler; defaults to the one in ~/.emscripten.')
  parser.add_option('-s', '--setting',
                    dest='settings',
                    default=[],
                    action='append',
                    metavar='FOO=BAR',
                    help=('Overrides for settings defined in settings.js. '
                          'May occur multiple times.'))
  parser.add_option('-j', '--jcache',
                    action='store_true',
                    default=False,
                    help=('Enable jcache (ccache-like caching of compilation results, for faster incremental builds).'))

  # Convert to the same format that argparse would have produced.
  keywords, positional = parser.parse_args()
  if len(positional) != 1:
    raise RuntimeError('Must provide exactly one positional argument.')
  keywords.infile = os.path.abspath(positional[0])
  if isinstance(keywords.outfile, basestring):
    keywords.outfile = open(keywords.outfile, 'w')
  compiler_engine = keywords.compiler
  jcache = keywords.jcache

  temp_files.run_and_clean(lambda: main(keywords))

if __name__ == '__main__':
  _main()