fix corner case in assignments (#4522)

fixes #4521

lib/compress.js

@@ -9948,9 +9948,9 @@ merge(Compressor.prototype, {
                         operator: self.right.operator + "=",
                         left: self.left,
                         right: self.right.right,
-                    }).optimize(compressor);
+                    });
                 }
-                else if (self.right.right instanceof AST_SymbolRef
+                if (self.right.right instanceof AST_SymbolRef
                     && self.right.right.name == self.left.name
                     && ASSIGN_OPS_COMMUTATIVE[self.right.operator]
                     && !self.right.left.has_side_effects(compressor)) {
@@ -9959,7 +9959,7 @@ merge(Compressor.prototype, {
                         operator: self.right.operator + "=",
                         left: self.left,
                         right: self.right.left,
-                    }).optimize(compressor);
+                    });
                 }
             }
             if ((self.operator == "-=" || self.operator == "+="

test/compress/assignments.js

@@ -461,3 +461,17 @@ issue_3949_2: {
     }
     expect_stdout: "100"
 }
+
+issue_4521: {
+    options = {
+        assignments: true,
+        dead_code: true,
+    }
+    input: {
+        var a = (a = 42 | a) ? console.log(a) : 0;
+    }
+    expect: {
+        var a = (a |= 42) ? console.log(a) : 0;
+    }
+    expect_stdout: "42"
+}