fix AST_Binary.lift_sequences() (#1621)

Commit eab99a1c fails to account for side effects from compound assignments.

1 files changed, 17 insertions, 20 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 66a4120e..53412a3f 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2999,14 +2999,6 @@ merge(Compressor.prototype, {
         return self;
     });
 
-    function has_side_effects_or_prop_access(node, compressor) {
-        var save_pure_getters = compressor.option("pure_getters");
-        compressor.options.pure_getters = false;
-        var ret = node.has_side_effects(compressor);
-        compressor.options.pure_getters = save_pure_getters;
-        return ret;
-    }
-
     AST_Binary.DEFMETHOD("lift_sequences", function(compressor){
         if (compressor.option("sequences")) {
             if (this.left instanceof AST_Seq) {
@@ -3014,18 +3006,23 @@ merge(Compressor.prototype, {
                 var x = seq.to_array();
                 this.left = x.pop();
                 x.push(this);
-                seq = AST_Seq.from_array(x).transform(compressor);
-                return seq;
-            }
-            if (this.right instanceof AST_Seq
-                && this instanceof AST_Assign
-                && !has_side_effects_or_prop_access(this.left, compressor)) {
-                var seq = this.right;
-                var x = seq.to_array();
-                this.right = x.pop();
-                x.push(this);
-                seq = AST_Seq.from_array(x).transform(compressor);
-                return seq;
+                return AST_Seq.from_array(x).optimize(compressor);
+            }
+            if (this.right instanceof AST_Seq && !this.left.has_side_effects(compressor)) {
+                var assign = this.operator == "=" && this.left instanceof AST_SymbolRef;
+                var root = this.right;
+                var cursor, seq = root;
+                while (assign || !seq.car.has_side_effects(compressor)) {
+                    cursor = seq;
+                    if (seq.cdr instanceof AST_Seq) {
+                        seq = seq.cdr;
+                    } else break;
+                }
+                if (cursor) {
+                    this.right = cursor.cdr;
+                    cursor.cdr = this;
+                    return root.optimize(compressor);
+                }
             }
         }
         return this;