Run multiple iterations of JSDCE, as more may be removable (#5855)

 * Run JSDCE with or without closure. It helps even if closure runs later. As we improve it further it may help more.
  * Add AJSDCE (aggressive JSDCE) which runs multiple iterations. This is enabled on -Os, -Oz builds.
  * Clean up how we add closure testing to tests in test_core.py, and add it to some -Os tests too, not just -O2, for more coverage.

Author: kripken

emcc.py

@@ -2355,20 +2355,21 @@ def do_binaryen(target, asm_target, options, memfile, wasm_binary_target,
   if options.opt_level >= 2:
     # minify the JS
     optimizer.do_minify() # calculate how to minify
-    if optimizer.cleanup_shell or optimizer.minify_whitespace or options.use_closure_compiler:
-      misc_temp_files.note(final)
+    if optimizer.cleanup_shell or options.use_closure_compiler:
       if DEBUG: save_intermediate('preclean', 'js')
+      # in -Os and -Oz, run AJSDCE (aggressive JS DCE, performs multiple iterations)
+      passes = ['noPrintMetadata', 'JSDCE' if options.shrink_level == 0 else 'AJSDCE', 'last']
+      if optimizer.minify_whitespace:
+        passes.append('minifyWhitespace')
+      misc_temp_files.note(final)
+      logging.debug('running cleanup on shell code: ' + ' '.join(passes))
+      final = shared.Building.js_optimizer_no_asmjs(final, passes)
+      if DEBUG: save_intermediate('postclean', 'js')
       if options.use_closure_compiler:
         logging.debug('running closure on shell code')
+        misc_temp_files.note(final)
         final = shared.Building.closure_compiler(final, pretty=not optimizer.minify_whitespace)
-      else:
-        assert optimizer.cleanup_shell
-        logging.debug('running cleanup on shell code')
-        passes = ['noPrintMetadata', 'JSDCE', 'last']
-        if optimizer.minify_whitespace:
-          passes.append('minifyWhitespace')
-        final = shared.Building.js_optimizer_no_asmjs(final, passes)
-      if DEBUG: save_intermediate('postclean', 'js')
+        if DEBUG: save_intermediate('postclosure', 'js')
   # replace placeholder strings with correct subresource locations
   if shared.Settings.SINGLE_FILE:
     f = open(final, 'r')

tests/optimizer/AJSDCE-output.js

@@ -0,0 +1,27 @@
+
+var z = fleefl();
+var zz = fleefl();
+function g(a) {
+ return a + 1;
+}
+Module["g"] = g;
+function h(a) {
+ return a + 1;
+}
+print(h(123));
+((function() {
+ var z = fleefl();
+ var zz = fleefl();
+ function g(a) {
+  return a + 1;
+ }
+ Module["g"] = g;
+ function hh(a) {
+  return a + 1;
+ }
+ print(hh(123));
+}))();
+function glue() {
+}
+glue();
+

tests/optimizer/AJSDCE.js

@@ -0,0 +1,61 @@
+
+// all unused
+var x;
+var y = 1;
+var z = fleefl();
+var xx, yy = 1, zz = fleefl(); // but zz must remain due to the side effects in the value
+function f(x, y, z) {
+  // shadow the x,y,z
+  x = y;
+  y = z;
+}
+
+// exported
+function g(a) {
+  return a+1;
+}
+Module['g'] = g;
+
+// used
+function h(a) {
+  var t; // unused
+  return a+1;
+}
+print(h(123));
+
+// inner workings
+(function() {
+  var x;
+  var y = 1;
+  var z = fleefl();
+  var xx, yy = 1, zz = fleefl();
+  function f(x, y, z) {
+    // shadow the x,y,z
+    x = y;
+    y = z;
+  }
+
+  // exported
+  function g(a) {
+    return a+1;
+  }
+  Module['g'] = g;
+
+  // used
+  function hh(a) {
+    var t; // unused
+    return a+1;
+  }
+  print(hh(123));
+})();
+
+function glue() {
+  function lookup() { // 2 passes needed for this one
+    throw 1;
+  }
+  function removable() { // first remove this
+    lookup();
+  }
+}
+glue();
+

tests/optimizer/JSDCE-output.js

@@ -21,4 +21,10 @@ print(h(123));
  }
  print(hh(123));
 }))();
+function glue() {
+ function lookup() {
+  throw 1;
+ }
+}
+glue();
 

tests/optimizer/JSDCE.js

@@ -49,3 +49,13 @@ print(h(123));
   print(hh(123));
 })();
 
+function glue() {
+  function lookup() { // 2 passes needed for this one
+    throw 1;
+  }
+  function removable() { // first remove this
+    lookup();
+  }
+}
+glue();
+

tests/test_core.py

@@ -55,6 +55,13 @@ def is_split_memory(self):
   def is_wasm(self):
     return 'BINARYEN' in str(self.emcc_args) or self.is_wasm_backend()
 
+  # Use closure in some tests for some additional coverage
+  def maybe_closure(self):
+    if '-O2' in self.emcc_args or '-Os' in self.emcc_args:
+      self.emcc_args += ['--closure', '1']
+      return True
+    return False
+
   def do_run_in_out_file_test(self, *path, **kwargs):
       test_path = path_from_root(*path)
 
@@ -882,8 +889,7 @@ def test_exceptions(self):
       Settings.EXCEPTION_DEBUG = 1
 
       Settings.DISABLE_EXCEPTION_CATCHING = 0
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       src = '''
         #include <stdio.h>
@@ -4089,8 +4095,7 @@ def test_langinfo(self):
 
   def test_files(self):
     self.banned_js_engines = [SPIDERMONKEY_ENGINE] # closure can generate variables called 'gc', which pick up js shell stuff
-    if '-O2' in self.emcc_args:
-      self.emcc_args += ['--closure', '1'] # Use closure here, to test we don't break FS stuff
+    if self.maybe_closure(): # Use closure here, to test we don't break FS stuff
       self.emcc_args = [x for x in self.emcc_args if x != '-g'] # ensure we test --closure 1 --memory-init-file 1 (-g would disable closure)
     elif '-O3' in self.emcc_args and not self.is_wasm():
       print('closure 2')
@@ -5107,8 +5112,7 @@ def test_sse1(self):
     orig_args = self.emcc_args
     for mode in [[], ['-s', 'SIMD=1']]:
       self.emcc_args = orig_args + mode + ['-msse']
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       self.do_run(open(path_from_root('tests', 'test_sse1.cpp'), 'r').read(), 'Success!')
 
@@ -5130,8 +5134,7 @@ def test_sse1_full(self):
     orig_args = self.emcc_args
     for mode in [[], ['-s', 'SIMD=1']]:
       self.emcc_args = orig_args + mode + ['-I' + path_from_root('tests'), '-msse']
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       self.do_run(open(path_from_root('tests', 'test_sse1_full.cpp'), 'r').read(), self.ignore_nans(native_result), output_nicerizer=self.ignore_nans)
 
@@ -5153,8 +5156,7 @@ def test_sse2_full(self):
     orig_args = self.emcc_args
     for mode in [[], ['-s', 'SIMD=1']]:
       self.emcc_args = orig_args + mode + ['-I' + path_from_root('tests'), '-msse2'] + args
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       self.do_run(open(path_from_root('tests', 'test_sse2_full.cpp'), 'r').read(), self.ignore_nans(native_result), output_nicerizer=self.ignore_nans)
 
@@ -5463,8 +5465,7 @@ def test_sqlite(self):
                  force_c=True)
 
   def test_zlib(self):
-    if '-O2' in self.emcc_args and 'ASM_JS=0' not in self.emcc_args: # without asm, closure minifies Math.imul badly
-      self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+    self.maybe_closure()
 
     assert 'asm2g' in test_modes
     if self.run_name == 'asm2g':

tests/test_other.py

@@ -1973,6 +1973,8 @@ def test_js_optimizer(self):
        ['JSDCE']),
       (path_from_root('tests', 'optimizer', 'JSDCE-hasOwnProperty.js'), open(path_from_root('tests', 'optimizer', 'JSDCE-hasOwnProperty-output.js')).read(),
        ['JSDCE']),
+      (path_from_root('tests', 'optimizer', 'AJSDCE.js'), open(path_from_root('tests', 'optimizer', 'AJSDCE-output.js')).read(),
+       ['AJSDCE']),
     ]:
       print(input, passes)