fix corner case in `conditionals` (#3577)

fixes #3576

1 files changed, 4 insertions, 11 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 43ee1126..26d17295 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6673,7 +6673,7 @@ merge(Compressor.prototype, {
                 && alt_tail instanceof AST_Assign
                 && seq_tail.operator == alt_tail.operator
                 && seq_tail.left.equivalent_to(alt_tail.left)
-                && (is_eq && !seq_tail.left.has_side_effects(compressor)
+                && (is_eq && seq_tail.left instanceof AST_SymbolRef
                     || !condition.has_side_effects(compressor)
                         && can_shift_lhs_of_tail(consequent)
                         && can_shift_lhs_of_tail(alternative))) {
@@ -6842,16 +6842,9 @@ merge(Compressor.prototype, {
         }
 
         function can_shift_lhs_of_tail(node) {
-            if (node === node.tail_node()) return true;
-            var exprs = node.expressions;
-            for (var i = exprs.length - 1; --i >= 0;) {
-                var expr = exprs[i];
-                if (!(expr instanceof AST_Assign) && expr.has_side_effects(compressor)
-                    || expr.operator != "="
-                    || expr.left.has_side_effects(compressor)
-                    || expr.right.has_side_effects(compressor)) return false;
-            }
-            return true;
+            return node === node.tail_node() || all(node.expressions.slice(0, -1), function(expr) {
+                return !expr.has_side_effects(compressor);
+            });
         }
 
         function pop_lhs(node) {