2 files changed, 28 insertions, 3 deletions
diff --git a/emscripten.py b/emscripten.py
index d33c16e7..5eb62ba2 100755
--- a/emscripten.py
+++ b/emscripten.py
@@ -123,15 +123,24 @@ def emscript(infile, settings, outfile, libraries=[]):
 
   # Save settings to a file to work around v8 issue 1579
   settings_file = temp_files.get('.txt').name
+  settings_text = json.dumps(settings)
   s = open(settings_file, 'w')
-  s.write(json.dumps(settings))
+  s.write(settings_text)
   s.close()
 
   # Phase 1 - pre
   if DEBUG: t = time.time()
   pre_file = temp_files.get('.pre.ll').name
-  open(pre_file, 'w').write(''.join(pre) + '\n' + meta)
-  out = shared.run_js(compiler, shared.COMPILER_ENGINE, [settings_file, pre_file, 'pre'] + libraries, stdout=subprocess.PIPE, cwd=path_from_root('src'))
+  pre_input = ''.join(pre) + '\n' + meta
+  out = None
+  if jcache:
+    pre_cache_key = JCache.get_key([pre_input, settings_text, ','.join(libraries)])
+    out = JCache.get(pre_cache_key)
+  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:
+      JCache.set(pre_cache_key, out)
   pre, forwarded_data = out.split('//FORWARDED_DATA:')
   forwarded_file = temp_files.get('.json').name
   open(forwarded_file, 'w').write(forwarded_data)
diff --git a/tools/shared.py b/tools/shared.py
index 1f3b5f20..06cbba68 100644
--- a/tools/shared.py
+++ b/tools/shared.py
@@ -1153,6 +1153,22 @@ class Cache:
     shutil.copyfile(creator(), cachename)
     return cachename
 
+class JCache:
+  # Generates a single key from multiple values
+  @staticmethod
+  def get_key(keys):
+    return ''
+
+  # Returns a cached value for a key (from get_key), if it exists
+  @staticmethod
+  def get(key):
+    return None
+
+  # Sets the cached value for a key (from get_key)
+  @staticmethod
+  def set(key, value):
+    pass
+
 # Compression of code and data for smaller downloads
 class Compression:
   on = False