use llvm internalive and globaldce to remove unneeded code before compiling to js

emcc

@@ -512,6 +512,11 @@ try:
   if llvm_opt_level > 0 and not LEAVE_INPUTS_RAW:
     if DEBUG: print >> sys.stderr, 'emcc: LLVM opts'
     shared.Building.llvm_opt(in_temp(target_basename + '.bc'), LLVM_INTERNAL_OPT_LEVEL, safe=llvm_opt_level < 2)
+  else:
+    # If possible, remove dead functions etc., this potentially saves a lot in the size of the generated code (and the time to compile it)
+    if not shared.Settings.BUILD_AS_SHARED_LIB:
+      if DEBUG: print >> sys.stderr, 'emcc: LLVM dead globals elimination'
+      shared.Building.llvm_opt(in_temp(target_basename + '.bc'), ['-internalize', '-globaldce'])
 
   # Emscripten
   try:
@@ -531,6 +536,7 @@ try:
 
   if not LEAVE_INPUTS_RAW:
     final = in_temp(target_basename + '.bc')
+    if DEBUG: save_intermediate('bc', 'bc')
     final = shared.Building.llvm_dis(final, final + '.ll')
     if DEBUG: save_intermediate('ll', 'll')
   else:

tools/shared.py

@@ -439,10 +439,14 @@ class Building:
     output = Popen(['python', DFE, filename + '.o.ll.orig', filename + '.o.ll'], stdout=PIPE).communicate()[0]
     assert os.path.exists(filename + '.o.ll'), 'Failed to run ll optimizations'
 
-  # Optional LLVM optimizations
+  # LLVM optimizations
+  # @param opt Either an integer, in which case it is the optimization level (-O1, -O2, etc.), or a list of raw
+  #            optimization passes passed to llvm opt
   @staticmethod
-  def llvm_opt(filename, level, safe=True):
-    output = Popen([LLVM_OPT, filename] + Building.pick_llvm_opts(level, safe) + ['-o=' + filename + '.opt.bc'], stdout=PIPE).communicate()[0]
+  def llvm_opt(filename, opts, safe=True):
+    if type(opts) is int:
+      opts = Building.pick_llvm_opts(opts, safe)
+    output = Popen([LLVM_OPT, filename] + opts + ['-o=' + filename + '.opt.bc'], stdout=PIPE).communicate()[0]
     assert os.path.exists(filename + '.opt.bc'), 'Failed to run llvm optimizations: ' + output
     shutil.move(filename + '.opt.bc', filename)
 
@@ -533,6 +537,10 @@ class Building:
       (which we do in do_ll_opts) - but even there we have issues (even in TA2) with instruction combining
       into i64s. In any case, the handpicked ones here should be safe and portable. They are also tuned for
       things that look useful.
+
+      An easy way to see LLVM's standard list of passes is
+
+        llvm-as < /dev/null | opt -std-compile-opts -disable-output -debug-pass=Arguments
     '''
     opts = []
     if optimization_level > 0:
@@ -552,6 +560,9 @@ class Building:
           opts.append('-tbaa')
           opts.append('-basicaa') # makes fannkuch slow but primes fast
 
+        if not Settings.BUILD_AS_SHARED_LIB:
+          opts.append('-internalize')
+
         opts.append('-globalopt')
         opts.append('-ipsccp')
         opts.append('-deadargelim')
@@ -609,7 +620,8 @@ class Building:
 
         opts.append('-strip-dead-prototypes')
 
-        if optimization_level > 2: opts.append('-globaldce')
+        if not Settings.BUILD_AS_SHARED_LIB:
+          opts.append('-globaldce')
 
         if optimization_level > 1: opts.append('-constmerge')