fix unsafe expansion of object literals (#2390)

lib/compress.js

@@ -4499,12 +4499,11 @@ merge(Compressor.prototype, {
             for (var i = values.length; --i >= 0;) {
                 if (values[i].key === self.property) {
                     var value = values[i].value;
-                    if (value instanceof AST_Function ? !value.contains_this() : !value.has_side_effects(compressor)) {
-                        var obj = self.expression.clone();
-                        obj.properties = obj.properties.slice();
-                        obj.properties.splice(i, 1);
-                        return make_sequence(self, [ obj, value ]).optimize(compressor);
-                    }
+                    if (value instanceof AST_Function ? value.contains_this() : value.has_side_effects(compressor)) break;
+                    var obj = self.expression.clone();
+                    obj.properties = obj.properties.slice();
+                    obj.properties.splice(i, 1);
+                    return make_sequence(self, [ obj, value ]).optimize(compressor);
                 }
             }
         }

test/compress/properties.js

@@ -841,3 +841,22 @@ lhs_prop_2: {
         "abc"[2] = "g";
     }
 }
+
+literal_duplicate_key_side_effects: {
+    options = {
+        unsafe: true,
+    }
+    input: {
+        console.log({
+            a: "FAIL",
+            a: console.log ? "PASS" : "FAIL"
+        }.a);
+    }
+    expect: {
+        console.log({
+            a: "FAIL",
+            a: console.log ? "PASS" : "FAIL"
+        }.a);
+    }
+    expect_stdout: "PASS"
+}