it's safe to negate expression in !EXP only in boolean context

#kendo

lib/compress.js

@@ -53,6 +53,7 @@ function Compressor(options, false_by_default) {
         dead_code     : !false_by_default,
         drop_debugger : !false_by_default,
         unsafe        : !false_by_default,
+        unsafe_comps  : false,
         conditionals  : !false_by_default,
         comparisons   : !false_by_default,
         evaluate      : !false_by_default,
@@ -427,12 +428,23 @@ merge(Compressor.prototype, {
             var ret = [], prev = null;
             statements.forEach(function(stat){
                 if (prev) {
-                    if (stat instanceof AST_For && stat.init && !(stat.init instanceof AST_Definitions)) {
-                        stat.init = cons_seq(stat.init);
-                    }
-                    else if (stat instanceof AST_For && !stat.init) {
-                        stat.init = prev.body;
-                        ret.pop();
+                    if (stat instanceof AST_For) {
+                        var opera = {};
+                        try {
+                            prev.body.walk(new TreeWalker(function(node){
+                                if (node instanceof AST_Binary && node.operator == "in")
+                                    throw opera;
+                            }));
+                            if (stat.init && !(stat.init instanceof AST_Definitions)) {
+                                stat.init = cons_seq(stat.init);
+                            }
+                            else if (!stat.init) {
+                                stat.init = prev.body;
+                                ret.pop();
+                            }
+                        } catch(ex) {
+                            if (ex !== opera) throw ex;
+                        }
                     }
                     else if (stat instanceof AST_If) {
                         stat.condition = cons_seq(stat.condition);
@@ -692,7 +704,7 @@ merge(Compressor.prototype, {
         });
         def(AST_Binary, function(compressor){
             var self = this.clone(), op = this.operator;
-            if (compressor.option("comparisons") && compressor.option("unsafe")) {
+            if (compressor.option("unsafe_comps")) {
                 switch (op) {
                   case "<=" : self.operator = ">"  ; return self;
                   case "<"  : self.operator = ">=" ; return self;
@@ -1434,9 +1446,9 @@ merge(Compressor.prototype, {
                 compressor.warn("Boolean expression always true [{file}:{line},{col}]", self.start);
                 return make_node(AST_True, self);
             }
-        }
-        if (e instanceof AST_Binary) {
-            self = best_of(self, e.negate(compressor));
+            if (e instanceof AST_Binary && self.operator == "!") {
+                self = best_of(self, e.negate(compressor));
+            }
         }
         return self.evaluate(compressor)[0];
     });

package.json

@@ -3,7 +3,7 @@
     "description": "JavaScript parser, mangler/compressor and beautifier toolkit",
     "homepage": "http://lisperator.net/uglifyjs",
     "main": "tools/node.js",
-    "version": "2.1.4",
+    "version": "2.1.5",
     "engines": { "node" : ">=0.4.0" },
     "maintainers": [{
         "name": "Mihai Bazon",

test/compress/sequences.js

@@ -127,3 +127,35 @@ lift_sequences_4: {
         x = baz;
     }
 }
+
+for_sequences: {
+    options = { sequences: true };
+    input: {
+        // 1
+        foo();
+        bar();
+        for (; false;);
+        // 2
+        foo();
+        bar();
+        for (x = 5; false;);
+        // 3
+        x = (foo in bar);
+        for (; false;);
+        // 4
+        x = (foo in bar);
+        for (y = 5; false;);
+    }
+    expect: {
+        // 1
+        for (foo(), bar(); false;);
+        // 2
+        for (foo(), bar(), x = 5; false;);
+        // 3
+        x = (foo in bar);
+        for (; false;);
+        // 4
+        x = (foo in bar);
+        for (y = 5; false;);
+    }
+}