fix corner case in `reduce_vars` (#3895)

fixes #3894

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/compress.js b/lib/compress.js
index f7c0af30..8cf7262a 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -741,6 +741,11 @@ merge(Compressor.prototype, {
                             if (j < 0) return value;
                             return iife.args[j] || make_node(AST_Undefined, iife);
                         };
+                        d.fixed.reduce_arg = function() {
+                            var j = fn.argnames.indexOf(arg);
+                            if (j < 0 || j >= iife.args.length) return;
+                            iife.args[j] = make_node(AST_Number, iife.args[j], { value: 0 });
+                        };
                         tw.loop_ids[d.id] = tw.in_loop;
                         mark(tw, d, true);
                     } else {
@@ -7566,6 +7571,7 @@ merge(Compressor.prototype, {
                     }));
                 } else {
                     value = fixed.optimize(compressor);
+                    if (def.fixed.reduce_arg) def.fixed.reduce_arg();
                 }
                 def.replaced++;
                 return value;