From 6e105c5ca6c95f6159d91f74df92020f33ae2f99 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Fri, 25 Sep 2020 15:00:20 +0100
Subject: [PATCH] enhance `merge_vars` (#4152)

---
 lib/compress.js             |  4 +---
 test/compress/merge_vars.js | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 517f29fd..3f7eee68 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4538,9 +4538,7 @@ merge(Compressor.prototype, {
             if (def.id in references) {
                 var refs = references[def.id];
                 if (!refs) return;
-                if (write ? refs.start !== segment : refs.start.block !== segment.block) {
-                    return references[def.id] = false;
-                }
+                if (refs.start.block !== segment.block) return references[def.id] = false;
                 refs.push(sym);
                 refs.end = segment;
                 if (def.id in prev) {
diff --git a/test/compress/merge_vars.js b/test/compress/merge_vars.js
index b5148669..b86b0e99 100644
--- a/test/compress/merge_vars.js
+++ b/test/compress/merge_vars.js
@@ -2800,3 +2800,25 @@ lambda_reuse: {
         "string",
     ]
 }
+
+conditional_write: {
+    options = {
+        merge_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = "FAIL", b;
+        if (console)
+            a = "PASS";
+        b = [a, 42].join();
+        console.log(b);
+    }
+    expect: {
+        var b = "FAIL", b;
+        if (console)
+            b = "PASS";
+        b = [b, 42].join();
+        console.log(b);
+    }
+    expect_stdout: "PASS,42"
+}
-- 
2.34.1