fix corner case

add tests

lib/compress.js

@@ -3418,7 +3418,7 @@ merge(Compressor.prototype, {
 
     function if_break_in_loop(self, compressor) {
         var first = self.body instanceof AST_BlockStatement ? self.body.body[0] : self.body;
-        if (is_break(first)) {
+        if (compressor.option("dead_code") && is_break(first)) {
             var body = [];
             if (self.init instanceof AST_Statement) {
                 body.push(self.init);
@@ -3432,6 +3432,7 @@ merge(Compressor.prototype, {
                     body: self.condition
                 }));
             }
+            extract_declarations_from_unreachable_code(compressor, self.body, body);
             return make_node(AST_BlockStatement, self, {
                 body: body
             });
@@ -3481,7 +3482,7 @@ merge(Compressor.prototype, {
             }
             self = if_break_in_loop(self, compressor);
         }
-    };
+    }
 
     OPT(AST_For, function(self, compressor){
         if (!compressor.option("loops")) return self;

test/compress/loops.js

@@ -495,6 +495,7 @@ dead_code_condition: {
 
 issue_2740_1: {
     options = {
+        dead_code: true,
         loops: true,
     }
     input: {
@@ -521,6 +522,7 @@ issue_2740_1: {
 
 issue_2740_2: {
     options = {
+        dead_code: true,
         loops: true,
         passes: 2,
     }
@@ -533,3 +535,73 @@ issue_2740_2: {
         x();
     }
 }
+
+issue_2740_3: {
+    options = {
+        dead_code: true,
+        loops: true,
+    }
+    input: {
+        L1: for (var x = 0; x < 3; x++) {
+            L2: for (var y = 0; y < 2; y++) {
+                break L1;
+            }
+        }
+        console.log(x, y);
+    }
+    expect: {
+        L1: for (var x = 0; x < 3; x++)
+            for (var y = 0; y < 2; y++)
+                break L1;
+        console.log(x, y);
+    }
+    expect_stdout: "0 0"
+}
+
+issue_2740_4: {
+    options = {
+        dead_code: true,
+        loops: true,
+        passes: 2,
+    }
+    input: {
+        L1: for (var x = 0; x < 3; x++) {
+            L2: for (var y = 0; y < 2; y++) {
+                break L2;
+            }
+        }
+        console.log(x, y);
+    }
+    expect: {
+        for (var x = 0; x < 3; x++) {
+            var y = 0;
+            y < 2;
+        }
+        console.log(x, y);
+    }
+    expect_stdout: "3 0"
+}
+
+issue_2740_5: {
+    options = {
+        dead_code: true,
+        loops: true,
+        passes: 2,
+    }
+    input: {
+        L1: for (var x = 0; x < 3; x++) {
+            break L1;
+            L2: for (var y = 0; y < 2; y++) {
+                break L2;
+            }
+        }
+        console.log(x, y);
+    }
+    expect: {
+        var x = 0;
+        x < 3;
+        var y;
+        console.log(x,y);
+    }
+    expect_stdout: "0 undefined"
+}