fix corner cases in inline & unused (#4509)

fixes #4508

lib/compress.js

@@ -5674,12 +5674,11 @@ merge(Compressor.prototype, {
                             var write_only = def.value.write_only;
                             var value = def.value.drop_side_effect_free(compressor);
                             if (def.value !== value) {
-                                def.value = value && make_sequence(def.value, [
-                                    value,
-                                    make_node(AST_Number, def.value, {
-                                        value: 0
-                                    }),
-                                ]);
+                                def.value = null;
+                                if (value) {
+                                    AST_Node.warn("Side effects in last use of variable {name} [{file}:{line},{col}]", template(def.name));
+                                    side_effects.push(value);
+                                }
                             } else if (def.value.write_only !== write_only) {
                                 def.value.write_only = write_only;
                             }
@@ -8139,7 +8138,7 @@ merge(Compressor.prototype, {
                         return node;
                     }
                 }
-                var insert, in_loop, scope;
+                var arg_used, insert, in_loop, scope;
                 if (replacing && can_inject_symbols()) {
                     fn._squeezed = true;
                     if (exp !== fn) fn.parent_scope = exp.scope;
@@ -8453,8 +8452,9 @@ merge(Compressor.prototype, {
                 }
             }
             var inline = compressor.option("inline");
-            var used = Object.create(defined);
-            if (!can_inject_args(defined, used, inline >= 2 && safe_to_inject)) return false;
+            arg_used = Object.create(defined);
+            if (!can_inject_args(defined, arg_used, inline >= 2 && safe_to_inject)) return false;
+            var used = Object.create(arg_used);
             if (!can_inject_vars(defined, used, inline >= 3 && safe_to_inject)) return false;
             return !in_loop || in_loop.length == 0 || !is_reachable(fn, in_loop);
         }
@@ -8558,10 +8558,7 @@ merge(Compressor.prototype, {
                         name.thedef = redef;
                     }
                     append_var(decls, expressions, name, var_def.value);
-                    if (in_loop && all(fn.argnames, function(argname) {
-                        if (argname instanceof AST_DefaultValue) argname = argname.name;
-                        return argname.name != name.name;
-                    })) {
+                    if (in_loop && !HOP(arg_used, name.name)) {
                         var def = fn.variables.get(name.name);
                         var sym = make_node(AST_SymbolRef, name, name);
                         def.references.push(sym);

test/compress/destructured.js

@@ -2356,3 +2356,31 @@ issue_4504: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4508: {
+    options = {
+        inline: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        for (var i = 0; i < 2; i++)
+            (function f([ a ]) {
+                var a = console.log(a) && b, b = null;
+            })([ "PASS" ]);
+    }
+    expect: {
+        for (var i = 0; i < 2; i++)
+            [ [ a ] ] = [ [ "PASS" ] ],
+            b = void 0,
+            a = console.log(a) && b,
+            b = null,
+            void 0;
+        var a, b;
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+    ]
+    node_version: ">=6"
+}

test/compress/drop-unused.js

@@ -2669,8 +2669,7 @@ issue_3956: {
         })();
     }
     expect: {
-        var c, d;
-        c += 0,
+        var d;
         console.log(NaN),
         d = 1 ^ console.log(1),
         console.log(d);
@@ -2703,13 +2702,13 @@ issue_3962_1: {
     }
     expect: {
         var a = 0;
-        a = (function(c) {
+        (function(c) {
             do {
                 console;
                 0..toString();
             } while (0);
             if (c) console.log("PASS");
-        }(1), 0);
+        })(1);
         void 0;
     }
     expect_stdout: "PASS"
@@ -2736,13 +2735,13 @@ issue_3962_2: {
     }
     expect: {
         var a = 0;
-        a = (function(c) {
+        (function(c) {
             do {
                 console;
                 0..toString();
             } while (0);
             if (c) console.log("PASS");
-        }(1), 0);
+        })(1);
     }
     expect_stdout: "PASS"
 }
@@ -2799,7 +2798,9 @@ issue_4017: {
         var a = 0;
         console.log(function() {
             c &= 0;
-            var c = (a++, A = a, 0);
+            var c;
+            a++,
+            A = a;
         }());
     }
     expect_stdout: "undefined"