improve side effect detection in js optimizer

1 files changed, 7 insertions, 8 deletions

diff --git a/tools/js-optimizer.js b/tools/js-optimizer.js
index da6fe982..ed936f5f 100644
--- a/tools/js-optimizer.js
+++ b/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