fix corner case with default values (#4484)

fixes #4483

test/compress/default-values.js

@@ -1206,3 +1206,24 @@ issue_4468: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_4483: {
+    options = {
+        conditionals: true,
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        if (console)
+            var [ a = "FAIL" ] = [], b = a = "PASS";
+        console.log(b);
+    }
+    expect: {
+        var a, b;
+        console && ([ a = "FAIL" ] = [], b = "PASS");
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}

test/reduce.js

@@ -124,7 +124,6 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
 
             // ignore lvalues
             if (parent instanceof U.AST_Assign && parent.left === node) return;
-            if (parent instanceof U.AST_DestructuredArray) return;
             if (parent instanceof U.AST_DestructuredKeyVal && parent.value === node) return;
             if (parent instanceof U.AST_Unary && parent.expression === node) switch (parent.operator) {
               case "++":