enhance collapse_vars, unsafe & unused (#5868)

lib/compress.js

@@ -2693,13 +2693,13 @@ Compressor.prototype.compress = function(node) {
                 }
                 if (node instanceof AST_ObjectIdentity) return symbol_in_lvalues(node, parent);
                 if (node instanceof AST_PropAccess) {
-                    if (side_effects) return true;
                     var exp = node.expression;
-                    if (exp instanceof AST_SymbolRef && is_arguments(exp.definition())) return true;
                     if (compressor.option("unsafe")) {
                         if (is_undeclared_ref(exp) && global_names[exp.name]) return false;
                         if (is_static_fn(exp)) return false;
                     }
+                    if (exp instanceof AST_SymbolRef && is_arguments(exp.definition())) return true;
+                    if (side_effects) return true;
                     if (!well_defined) return true;
                     if (value_def) return false;
                     if (!in_try && lhs_local) return false;
@@ -2708,6 +2708,7 @@ Compressor.prototype.compress = function(node) {
                 }
                 if (node instanceof AST_Spread) return true;
                 if (node instanceof AST_SymbolRef) {
+                    if (is_undeclared_ref(node) && node.is_declared(compressor)) return false;
                     if (symbol_in_lvalues(node, parent)) return !is_direct_assignment(node, parent);
                     if (side_effects && may_modify(node)) return true;
                     var def = node.definition();
@@ -8219,23 +8220,34 @@ Compressor.prototype.compress = function(node) {
                     }
                     if (!native) {
                         elements.length = node.elements.length;
-                    } else if (!node.rest) switch (elements.length) {
+                    } else if (!node.rest) SHORTHAND: switch (elements.length) {
                       case 0:
                         if (node === root) break;
                         if (drop) value = value.drop_side_effect_free(compressor);
                         return null;
-                      case 1:
+                      default:
                         if (!drop) break;
                         if (!unwind) break;
                         if (node === root) break;
-                        var sym = elements[0];
+                        var pos = elements.length, sym;
+                        while (--pos >= 0) {
+                            var element = elements[pos];
+                            if (element) {
+                                sym = element;
+                                break;
+                            }
+                        }
+                        if (pos < 0) break;
+                        for (var i = pos; --i >= 0;) {
+                            if (elements[i]) break SHORTHAND;
+                        }
                         if (sym.has_side_effects(compressor)) break;
                         if (value.has_side_effects(compressor) && sym.match_symbol(function(node) {
                             return node instanceof AST_PropAccess;
                         })) break;
                         value = make_node(AST_Sub, node, {
                             expression: value,
-                            property: make_node(AST_Number, node, { value: 0 }),
+                            property: make_node(AST_Number, node, { value: pos }),
                         });
                         return sym;
                     }

test/compress/collapse_vars.js

@@ -4996,7 +4996,7 @@ cascade_forin: {
     ]
 }
 
-unsafe_builtin: {
+unsafe_builtin_1: {
     options = {
         collapse_vars: true,
         pure_getters: "strict",
@@ -5020,6 +5020,46 @@ unsafe_builtin: {
     expect_stdout: "1 4"
 }
 
+unsafe_builtin_2: {
+    options = {
+        collapse_vars: true,
+        toplevel: true,
+        unsafe: true,
+        unused: true,
+    }
+    input: {
+        A = "PASS";
+        var a = A;
+        console.log(a);
+    }
+    expect: {
+        console.log(A = "PASS");
+    }
+    expect_stdout: "PASS"
+}
+
+unsafe_builtin_3: {
+    options = {
+        collapse_vars: true,
+        unsafe: true,
+        unused: true,
+    }
+    input: {
+        A = "PASS";
+        (function() {
+            var a = A;
+            console.log(a);
+        })();
+    }
+    expect: {
+        A = "PASS";
+        (function() {
+            console.log(A);
+        })();
+    }
+    expect_stdout: "PASS"
+}
+
 return_1: {
     options = {
         collapse_vars: true,
@@ -7350,30 +7390,39 @@ substitution_assign: {
             b = 1 + (b = a);
             console.log(a, b);
         }
+        function f4(a, b) {
+            b = 1 + (a = b);
+            console.log(a, b);
+        }
         f1(42, "foo");
         f2(42, "foo");
         f3(42, "foo");
+        f4("bar", 41);
     }
     expect: {
         function f1(a, b) {
             console.log(f1 = a, a);
         }
         function f2(a, b) {
-            a = 1 + (b = a);
-            console.log(a, b);
+            console.log(a = 1 + (b = a), b);
         }
         function f3(a, b) {
-            b = 1 + (b = a);
+            console.log(a, b = 1 + (b = a));
+        }
+        function f4(a, b) {
+            b = 1 + (a = b);
             console.log(a, b);
         }
         f1(42, "foo");
         f2(42, "foo");
         f3(42, "foo");
+        f4("bar", 41);
     }
     expect_stdout: [
         "42 42",
         "43 42",
         "42 43",
+        "41 42",
     ]
 }
 

test/compress/destructured.js

@@ -1339,7 +1339,7 @@ maintain_position_var: {
     }
     expect: {
         A = "FAIL";
-        var [ , b ] = [ A ];
+        var b = [ A ][1];
         console.log(b || "PASS");
     }
     expect_stdout: "PASS"