fix corner case in hoist_props (#3412)

fixes #3411

lib/compress.js

@@ -519,7 +519,7 @@ merge(Compressor.prototype, {
             if (parent instanceof AST_Call && node === parent.expression) return;
             if (parent instanceof AST_Sequence && node !== parent.tail_node()) return;
             if (parent instanceof AST_SimpleStatement) return;
-            if (parent instanceof AST_Unary) return;
+            if (parent instanceof AST_Unary && !unary_side_effects[parent.operator]) return;
             d.direct_access = true;
         }
 
@@ -4067,6 +4067,16 @@ merge(Compressor.prototype, {
                 }));
                 return make_sequence(node, assignments);
             }
+            if (node instanceof AST_Unary
+                && !unary_side_effects[node.operator]
+                && node.expression instanceof AST_SymbolRef
+                && node.expression.definition().id in defs_by_id) {
+                node = node.clone();
+                node.expression = make_node(AST_Object, node, {
+                    properties: []
+                });
+                return node;
+            }
             if (node instanceof AST_VarDef && can_hoist(node.name, node.value, 0)) {
                 descend(node, this);
                 var defs = new Dictionary();