fix corner case in `collapse_vars` (#3898)

fixes #3897

1 files changed, 6 insertions, 4 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 93dbe063..36a04a70 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1855,7 +1855,12 @@ merge(Compressor.prototype, {
             }
 
             function foldable(expr) {
+                var lhs_ids = Object.create(null);
+                var marker = new TreeWalker(function(node) {
+                    if (node instanceof AST_SymbolRef) lhs_ids[node.definition().id] = true;
+                });
                 while (expr instanceof AST_Assign && expr.operator == "=") {
+                    expr.left.walk(marker);
                     expr = expr.right;
                 }
                 if (expr instanceof AST_SymbolRef) {
@@ -1871,12 +1876,9 @@ merge(Compressor.prototype, {
                 if (!(lhs instanceof AST_SymbolRef)) return false;
                 if (!invariant(expr)) return false;
                 var circular;
-                var def = lhs.definition();
                 expr.walk(new TreeWalker(function(node) {
                     if (circular) return true;
-                    if (node instanceof AST_SymbolRef && node.definition() === def) {
-                        circular = true;
-                    }
+                    if (node instanceof AST_SymbolRef && lhs_ids[node.definition().id]) circular = true;
                 }));
                 return !circular && rhs_exact_match;