Don't swap binary ops when "use asm" is in effect.

Refs #167

lib/ast.js

@@ -945,6 +945,9 @@ TreeWalker.prototype = {
             if (x instanceof type) return x;
         }
     },
+    has_directive: function(type) {
+        return this.find_parent(AST_Scope).has_directive(type);
+    },
     in_boolean_context: function() {
         var stack = this.stack;
         var i = stack.length, self = stack[--i];

lib/compress.js

@@ -1765,7 +1765,8 @@ merge(Compressor.prototype, {
     var commutativeOperators = makePredicate("== === != !== * & | ^");
 
     OPT(AST_Binary, function(self, compressor){
-        function reverse(op, force) {
+        var reverse = compressor.has_directive("use asm") ? noop
+            : function(op, force) {
                 if (force || !(self.left.has_side_effects() || self.right.has_side_effects())) {
                     if (op) self.operator = op;
                     var tmp = self.left;