js optimizer pass to simplify certain bit ops

emcc

@@ -219,8 +219,9 @@ if header: # header or such
 
 if TEMP_DIR:
   temp_dir = TEMP_DIR
-  if not os.path.exists(temp_dir):
-    os.makedirs(temp_dir)
+  if os.path.exists(temp_dir):
+    shutil.rmtree(temp_dir) # clear it
+  os.makedirs(temp_dir)
 else:
   temp_dir = tempfile.mkdtemp()
 
@@ -386,14 +387,17 @@ try:
     # eliminator
     final = shared.Building.eliminator(final)
 
+    # js optimizer pre-pass
+    final = shared.Building.js_optimizer(final, 'simplifyExpressionsPre')
+
   if closure:
     if DEBUG: print >> sys.stderr, 'emcc: running closure'
     final = shared.Building.closure_compiler(final)
 
   if opt_level >= 1:
-    # js optimizer
+    # js optimizer post-pass
     if DEBUG: print >> sys.stderr, 'emcc: running post-closure post-opts'
-    final = shared.Building.js_optimizer(final, 'simplifyExpressions')
+    final = shared.Building.js_optimizer(final, 'simplifyExpressionsPost')
 
   # If we were asked to also generate HTML, do that
   if final_suffix == 'html':

tests/runner.py

@@ -4953,7 +4953,6 @@ Options that are modified or new in %s include:
           # Verify optimization level etc. in the generated code
           # XXX these are quite sensitive, and will need updating when code generation changes
           generated = open('something.js').read() # TODO: parse out the _main function itself, not support code, if the tests below need that some day
-          assert ('|0)/2)|0)' in generated or '| 0) / 2 | 0)' in generated) == (opt_level <= 2), 'corrections should be in opt <= 2'
           assert 'new Uint16Array' in generated and 'new Uint32Array' in generated, 'typed arrays 2 should be used by default'
           assert 'SAFE_HEAP' not in generated, 'safe heap should not be used by default'
           assert ': while(' not in generated, 'when relooping we also js-optimize, so there should be no labelled whiles'
@@ -4961,6 +4960,8 @@ Options that are modified or new in %s include:
             assert 'Module._main = ' in generated, 'closure compiler should have been run'
           else:
             # closure has not been run, we can do some additional checks. TODO: figure out how to do these even with closure
+            assert 'Module._main = ' not in generated, 'closure compiler should not have been run'
+            # XXX find a way to test this: assert ('& 255' in generated or '&255' in generated) == (opt_level <= 2), 'corrections should be in opt <= 2'
             assert ('(__label__)' in generated) == (opt_level <= 1), 'relooping should be in opt >= 2'
             assert ('assert(STACKTOP < STACK_MAX)' in generated) == (opt_level == 0), 'assertions should be in opt == 0'
             assert 'var $i;' in generated, 'micro opts should always be on'
@@ -5081,7 +5082,7 @@ Options that are modified or new in %s include:
     def test_js_optimizer(self):
       input = open(path_from_root('tools', 'test-js-optimizer.js')).read()
       expected = open(path_from_root('tools', 'test-js-optimizer-output.js')).read()
-      output = Popen([NODE_JS, JS_OPTIMIZER, 'unGlobalize', 'removeAssignsToUndefined', 'simplifyExpressions', 'loopOptimizer'],
+      output = Popen([NODE_JS, JS_OPTIMIZER, 'unGlobalize', 'removeAssignsToUndefined', 'simplifyExpressionsPre', 'simplifyExpressionsPost', 'loopOptimizer'],
                      stdin=PIPE, stdout=PIPE).communicate(input)[0]
       self.assertIdentical(expected, output.replace('\n\n', '\n'))
 
@@ -5122,8 +5123,6 @@ else:
   print 'Benchmarking JS engine:', JS_ENGINE
 
   Building.COMPILER_TEST_OPTS = []
-  # TODO: Use other js optimizer options, like remove assigns to undefined (seems to slow us down more than speed us up)
-  POST_OPTIMIZATIONS = [['js-optimizer', 'loopOptimizer'], 'eliminator', 'closure', ['js-optimizer', 'simplifyExpressions']]
 
   TEST_REPS = 10
   TOTAL_TESTS = 7

tools/js-optimizer.js

@@ -260,7 +260,44 @@ function removeUnneededLabelSettings(ast) {
 }
 
 // Various expression simplifications
-function simplifyExpressions(ast) {
+function simplifyExpressionsPre(ast) {
+  // When there is a bunch of math like (((8+5)|0)+12)|0, only the external |0 is needed, one correction is enough.
+  // At each node, ((X|0)+Y)|0 can be transformed into (X+Y): The inner corrections are not needed
+  // TODO: Is the same is true for 0xff, 0xffff?
+
+  function simplifyBitops(ast) {
+    var SAFE_BINARY_OPS = set('+', '-', '*', '/', '%', '|');
+    var ZERO = ['num', 0];
+    var rerun = true;
+    while (rerun) {
+      rerun = false;
+      traverseGenerated(ast, function(node, type, stack) {
+        if (type == 'binary' && node[1] == '|' && (jsonCompare(node[2], ZERO) || jsonCompare(node[3], ZERO))) {
+          stack.push(1); // From here on up, no need for this kind of correction, it's done at the top
+
+          // We might be able to remove this correction
+          for (var i = stack.length-2; i >= 0; i--) {
+            if (stack[i] == 1) {
+              // Great, we can eliminate
+              rerun = true;
+              return jsonCompare(node[2], ZERO) ? node[3] : node[2];
+            } else if (stack[i] == -1) {
+              break; // Too bad, we can't
+            }
+          }
+        } else if ((type == 'binary' && node[1] in SAFE_BINARY_OPS) || type == 'num' || type == 'name') {
+          stack.push(0); // This node is safe in that it does not interfere with this optimization
+        } else {
+          stack.push(-1); // This node is dangerous! Give up if you see this before you see '1'
+        }
+      }, null, []);
+    }
+  }
+
+  simplifyBitops(ast);
+}
+
+function simplifyExpressionsPost(ast) {
   // We often have branchings that are simplified so one end vanishes, and
   // we then get
   //   if (!(x < 5))
@@ -373,7 +410,8 @@ var passes = {
   unGlobalize: unGlobalize,
   removeAssignsToUndefined: removeAssignsToUndefined,
   //removeUnneededLabelSettings: removeUnneededLabelSettings,
-  simplifyExpressions: simplifyExpressions,
+  simplifyExpressionsPre: simplifyExpressionsPre,
+  simplifyExpressionsPost: simplifyExpressionsPost,
   loopOptimizer: loopOptimizer
 };
 

tools/test-js-optimizer-output.js

@@ -79,6 +79,9 @@ function ignoreLoopy() {
   }
 }
 function bits() {
-  print((($s & 65535) + ((($f & 65535) << 16 >> 16) * (($f & 65535) << 16 >> 16) | 0 | 0) % 256 | 0) & 65535);
+  print((($s & 65535) + (($f & 65535) << 16 >> 16) * (($f & 65535) << 16 >> 16) % 256 | 0) & 65535);
 }
-// EMSCRIPTEN_GENERATED_FUNCTIONS: ["abc", "xyz", "xyz2", "expr", "loopy", "bits"]
+function maths() {
+  __ZN6b2Vec2C1Ev($this1 + 20 + 8 + 8 + 8 + 8 + 8 + 8 + 8 | 0);
+}
+// EMSCRIPTEN_GENERATED_FUNCTIONS: ["abc", "xyz", "xyz2", "expr", "loopy", "bits", "maths"]

tools/test-js-optimizer.js

@@ -83,5 +83,8 @@ function ignoreLoopy() {
 function bits() { // TODO: optimize this!
   print((($s & 65535) + ((($f & 65535) << 16 >> 16) * (($f & 65535) << 16 >> 16) | 0 | 0) % 256 | 0) & 65535);
 }
-// EMSCRIPTEN_GENERATED_FUNCTIONS: ["abc", "xyz", "xyz2", "expr", "loopy", "bits"]
+function maths() {
+  __ZN6b2Vec2C1Ev(((((((($this1 + 20 | 0 | 0) + 8 | 0) + 8 | 0) + 8 | 0) + 8 | 0) + 8 | 0) + 8 | 0) + 8 | 0);
+}
+// EMSCRIPTEN_GENERATED_FUNCTIONS: ["abc", "xyz", "xyz2", "expr", "loopy", "bits", "maths"]