improve side effect detection in js optimizer

Author: kripken

Diff for: tools/js-optimizer.js

@@ -783,14 +783,13 @@ function simplifyExpressionsPost(ast) {
   simplifyNotComps(ast);
 }
 
-function hasSideEffects(node) { // this is 99% incomplete and wrong! It just works on __label__ == X and number literals
-  if (node[0] == 'num') return false;
-  if (node[0] == 'binary' && (node[1] == '==' || node[1] == '!=') && node[2][0] == 'name' &&
-      node[3][0] == 'num') {
-    return false;
-  } else {
-    return true;
-  }
+var NO_SIDE_EFFECTS = set('num', 'name');
+
+function hasSideEffects(node) { // this is 99% incomplete!
+  if (node[0] in NO_SIDE_EFFECTS) return false;
+  if (node[0] == 'unary-prefix' && node[1] == '!') return hasSideEffects(node[2]);
+  if (node[0] == 'binary') return hasSideEffects(node[2]) || hasSideEffects(node[3]);
+  return true;
 }
 
 // Clear out empty ifs and blocks, and redundant blocks/stats and so forth

Diff for: tools/test-js-optimizer-output.js

@@ -173,6 +173,8 @@ function hoisting() {
   if (__label__ == 38) {
     var $79 = $_pr6;
   }
+  pause(9);
+  var $cmp70 = ($call69 | 0) != 0;
 }
 function innerShouldAlsoBeHoisted() {
   function hoisting() {

Diff for: tools/test-js-optimizer.js

@@ -216,6 +216,16 @@ function hoisting() {
       var $79 = $_pr6;
     }
   } while (0);
+  pause(9);
+  var $cmp70 = ($call69 | 0) != 0;
+  if ($cmp70) {
+    __label__ = 40;
+  } else {
+    __label__ = 41;
+  }
+  $if_then72$$if_end73$126 : do {
+    if (__label__ == 40) {} else if (__label__ == 41) {}
+  } while (0);
 }
 function innerShouldAlsoBeHoisted() {
   function hoisting() {