fix corner case in `switches` (#3585)

1 files changed, 24 insertions, 14 deletions

diff --git a/lib/compress.js b/lib/compress.js
index e97427bc..668293d2 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4872,25 +4872,23 @@ merge(Compressor.prototype, {
                     prev.body = [];
                 }
             }
-            if (default_branch
-                && default_branch.body.length == 0
-                && body[body.length - 1] === default_branch
-                && !branch.expression.has_side_effects(compressor)) {
-                default_branch.body = branch.body.slice();
-            } else {
-                body.push(branch);
-            }
+            body.push(branch);
         }
         while (i < len) eliminate_branch(self.body[i++], body[body.length - 1]);
-        if (body.length > 0) {
-            body[0].body = decl.concat(body[0].body);
-        }
-        self.body = body;
         while (branch = body[body.length - 1]) {
             var stat = branch.body[branch.body.length - 1];
             if (is_break(stat, compressor)) branch.body.pop();
-            if (branch.body.length || branch instanceof AST_Case
-                && (default_branch || branch.expression.has_side_effects(compressor))) break;
+            if (branch === default_branch) {
+                if (!is_body_empty(branch)) break;
+            } else if (branch.expression.has_side_effects(compressor)) {
+                break;
+            } else if (default_branch) {
+                if (!is_body_empty(default_branch)) break;
+                if (body[body.length - 2] !== default_branch) break;
+                default_branch.body = default_branch.body.concat(branch.body);
+                branch.body = [];
+            } else if (!is_body_empty(branch)) break;
+            eliminate_branch(branch);
             if (body.pop() === default_branch) default_branch = null;
         }
         if (body.length == 0) {
@@ -4900,6 +4898,8 @@ merge(Compressor.prototype, {
                 }))
             }).optimize(compressor);
         }
+        body[0].body = decl.concat(body[0].body);
+        self.body = body;
         if (body.length == 1 && (body[0] === exact_match || body[0] === default_branch)) {
             var has_break = false;
             var tw = new TreeWalker(function(node) {
@@ -4929,6 +4929,16 @@ merge(Compressor.prototype, {
             return node instanceof AST_Break && tw.loopcontrol_target(node) === self;
         }
 
+        function is_body_empty(branch) {
+            return all(branch.body, function(stat) {
+                return is_empty(stat)
+                    || stat instanceof AST_Defun
+                    || stat instanceof AST_Var && all(stat.definitions, function(var_def) {
+                        return !var_def.value;
+                    });
+            });
+        }
+
         function eliminate_branch(branch, prev) {
             if (prev && !aborts(prev)) {
                 prev.body = prev.body.concat(branch.body);