fix corner case in `collapse_vars` (#4587)

fixes #4586

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/compress.js b/lib/compress.js
index c6ebb34c..f4441775 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2345,6 +2345,7 @@ merge(Compressor.prototype, {
                     if (expr.operator == "="
                         && lhs instanceof AST_SymbolRef
                         && (def = lhs.definition()).references[0] === lhs
+                        && !(scope.uses_arguments && is_funarg(def))
                         && !compressor.exposed(def)) {
                         var referenced = def.references.length - def.replaced;
                         if (referenced > 1) mangleable_var(expr.right);
@@ -2357,6 +2358,7 @@ merge(Compressor.prototype, {
                     var def = expr.name.definition();
                     if (def.const_redefs) return;
                     if (!member(expr.name, def.orig)) return;
+                    if (scope.uses_arguments && is_funarg(def)) return;
                     var declared = def.orig.length - def.eliminated - (declare_only[def.name] || 0);
                     var referenced = def.references.length - def.replaced - (assignments[def.name] || 0);
                     if (declared > 1 && !(expr.name instanceof AST_SymbolFunarg)) {