fix corner case in assignments (#5671)

fixes #5670

lib/compress.js

@@ -11590,22 +11590,29 @@ Compressor.prototype.compress = function(node) {
             if (seq !== self) return seq.optimize(compressor);
         }
         if (compressor.option("assignments") && lazy_op[self.operator]) {
-            var assign = self.right;
+            var right = self.right;
             // a || (a = x) ---> a = a || x
             // a && (a = x) ---> a = a && x
             if (self.left instanceof AST_SymbolRef
-                && assign instanceof AST_Assign
+                && right instanceof AST_Assign
-                && assign.operator == "="
+                && right.operator == "="
-                && self.left.equals(assign.left)) {
+                && self.left.equals(right.left)) {
-                return make_node(AST_Assign, self, {
+                var left = right.left.clone();
+                var assign = make_node(AST_Assign, self, {
                     operator: "=",
-                    left: assign.left,
+                    left: left,
                     right: make_node(AST_Binary, self, {
                         operator: self.operator,
                         left: self.left,
-                        right: assign.right,
+                        right: right.right,
                     }),
-                }).optimize(compressor);
+                });
+                left.fixed = function() {
+                    return assign.right;
+                };
+                left.fixed.assigns = [ assign ];
+                left.definition().references.push(left);
+                return assign.optimize(compressor);
             }
         }
         if (compressor.option("comparisons")) switch (self.operator) {

test/compress/assignments.js

@@ -803,3 +803,23 @@ issue_4924_2: {
     expect_stdout: "PASS"
     node_version: ">=15"
 }
+
+issue_5670: {
+    options = {
+        assignments: true,
+        evaluate: true,
+        reduce_vars: true,
+    }
+    input: {
+        (function(a, b) {
+            a && a && (a = b += "") || console.log("PASS");
+        })();
+    }
+    expect: {
+        (function(a, b) {
+            a = a,
+            console.log("PASS");
+        })();
+    }
+    expect_stdout: "PASS"
+}