From 4291ecc77c6573a97ae151e9d49b4898a888a233 Mon Sep 17 00:00:00 2001
From: alexlamsl <alexlamsl@gmail.com>
Date: Sun, 26 Mar 2017 15:48:10 +0800
Subject: [PATCH] case expression with side effects can only be de-duplicated
 at the tail

---
 lib/compress.js         | 15 ++++++++-------
 test/compress/switch.js | 37 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 6fa0f7b3..1d009726 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2542,22 +2542,23 @@ merge(Compressor.prototype, {
                         continue;
                     }
                 }
+                var case_side_effects = branch instanceof AST_Case && branch.expression.has_side_effects(compressor);
                 if (aborts(branch)) {
                     var key = make_node(AST_BlockStatement, branch, branch).print_to_string();
                     var block;
                     if (!fallthrough && (block = blocks[key])) {
-                        block.body = [];
-                        body.splice(body.indexOf(block) + 1, 0, branch);
-                    } else {
-                        body.push(branch);
-                    }
+                        var insert = body.indexOf(block) + 1;
+                        if (insert == body.length || !case_side_effects) {
+                            block.body = [];
+                            body.splice(insert, 0, branch);
+                        } else body.push(branch);
+                    } else body.push(branch);
                     fallthrough = false;
                 } else {
                     body.push(branch);
                     fallthrough = true;
                 }
-                if (branch instanceof AST_Case && branch.expression.has_side_effects(compressor))
-                    blocks = Object.create(null);
+                if (case_side_effects) blocks = Object.create(null);
                 if (!fallthrough) blocks[key] = branch;
             }
             for (; i < len && fallthrough; i++) {
diff --git a/test/compress/switch.js b/test/compress/switch.js
index 758a80ad..546e1613 100644
--- a/test/compress/switch.js
+++ b/test/compress/switch.js
@@ -478,7 +478,7 @@ issue_1679: {
     expect_stdout: true
 }
 
-issue_1680: {
+issue_1680_1: {
     options = {
         dead_code: true,
         evaluate: true,
@@ -518,3 +518,38 @@ issue_1680: {
         "5",
     ]
 }
+
+issue_1680_2: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        var a = 100, b = 10;
+        switch (b) {
+          case a--:
+            break;
+          case b:
+            var c;
+            break;
+          case a:
+            break;
+          case a--:
+            break;
+        }
+        console.log(a, b);
+    }
+    expect: {
+        var a = 100, b = 10;
+        switch (b) {
+          case a--:
+          case a:
+            break;
+          case b:
+            var c;
+            break;
+          case a--:
+        }
+        console.log(a, b);
+    }
+    expect_stdout: true
+}