enhance unused (#4129)

lib/compress.js

@@ -4747,6 +4747,13 @@ merge(Compressor.prototype, {
                             }));
                         }
                     }
+                } else if (node instanceof AST_UnaryPostfix
+                    && node.expression instanceof AST_SymbolRef
+                    && indexOf_assign(node.expression.definition(), node) < 0) {
+                    return make_node(AST_UnaryPrefix, node, {
+                        operator: "+",
+                        expression: node.expression
+                    });
                 }
             }
             if (node instanceof AST_Call) calls_to_drop_args.push(node);

test/compress/collapse_vars.js

@@ -62,18 +62,18 @@ collapse_vars_side_effects_1: {
     expect: {
         function f1() {
             var s = "abcdef", i = 2;
-            console.log.bind(console)(s.charAt(i++), s.charAt(i++), s.charAt(4), 7);
+            console.log.bind(console)(s.charAt(i++), s.charAt(+i), s.charAt(4), 7);
         }
         function f2() {
             var s = "abcdef", i = 2;
-            console.log.bind(console)(s.charAt(i++), 5, s.charAt(i++), s.charAt(i++), 7);
+            console.log.bind(console)(s.charAt(i++), 5, s.charAt(i++), s.charAt(+i), 7);
         }
         function f3() {
             var s = "abcdef",
                 i = 2,
                 log = console.log.bind(console),
                 x = s.charAt(i++),
-                y = s.charAt(i++);
+                y = s.charAt(+i);
             log(x, s.charAt(4), y, 7);
         }
         function f4() {
@@ -3073,7 +3073,6 @@ issue_2298: {
     expect: {
         !function() {
             (function() {
-                0;
                 try {
                     !function(b) {
                         (void 0)[1] = "foo";

test/compress/drop-unused.js

@@ -1730,7 +1730,7 @@ chained_3: {
     expect: {
         console.log(function(a, b) {
             var c = b;
-            b++;
+            +b;
             return c;
         }(0, 2));
     }
@@ -2737,7 +2737,7 @@ issue_3962_1: {
                 0..toString();
             } while (0);
             if (c) console.log("PASS");
-        }((a--, 1)), 0);
+        }(1), 0);
         void 0;
     }
     expect_stdout: "PASS"
@@ -2770,7 +2770,7 @@ issue_3962_2: {
                 0..toString();
             } while (0);
             if (c) console.log("PASS");
-        }((a--, 1)), 0);
+        }(1), 0);
     }
     expect_stdout: "PASS"
 }
@@ -2853,11 +2853,11 @@ issue_4025: {
         console.log(a, b, d);
     }
     expect: {
-        var d, c = 0;
+        var c = 0;
         try {
             console.log(c);
         } finally {
-            d = c + 1;
+            var d = c + 1;
             c = 0;
         }
         console.log(1, 1, d);

test/compress/keep_fargs.js

@@ -306,7 +306,6 @@ issue_2298: {
     expect: {
         !function() {
             (function() {
-                0;
                 try {
                     !function() {
                         (void 0)[1] = "foo";

test/compress/reduce_vars.js

@@ -120,7 +120,7 @@ modified: {
     expect: {
         function f0() {
             var b = 2;
-            b++;
+            +b;
             console.log(2);
             console.log(4);
         }
@@ -5590,7 +5590,7 @@ lvalues_def_1: {
     }
     expect: {
         var b = 1;
-        var a = b++, b = NaN;
+        var a = +b, b = NaN;
         console.log(a, b);
     }
     expect_stdout: "1 NaN"