From ac002b6338a65d2323c092e34815d4db252da19a Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Thu, 18 Aug 2022 19:31:48 +0100
Subject: [PATCH] fix corner case in `reduce_vars` (#5624)

fixes #5623
---
 lib/compress.js              |  1 +
 test/compress/reduce_vars.js | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/lib/compress.js b/lib/compress.js
index 6473da50444..bcfee5a48d4 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1016,6 +1016,7 @@ Compressor.prototype.compress = function(node) {
             }
 
             function walk_prop(lhs) {
+                reset_flags(lhs);
                 if (lhs instanceof AST_Dot) {
                     walk_prop(lhs.expression);
                 } else if (lhs instanceof AST_Sub) {
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index 348d2c9eba4..002202617dc 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -7896,3 +7896,33 @@ issue_5434: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5623: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        var a = 0;
+        function f() {
+            var b = a;
+            a = b;
+        }
+        f && f((a++ && a).toString());
+        console.log(a);
+    }
+    expect: {
+        var a = 0;
+        function f() {
+            var b;
+            a = a;
+        }
+        f((a++ && a).toString());
+        console.log(a);
+    }
+    expect_stdout: "1"
+}