enhance `loops` (#3633)

1 files changed, 34 insertions, 11 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 6d398de2..fb7e66de 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -4718,8 +4718,8 @@ merge(Compressor.prototype, {
     });
 
     function if_break_in_loop(self, compressor) {
-        var first = self.body instanceof AST_BlockStatement ? self.body.body[0] : self.body;
-        if (compressor.option("dead_code") && is_break(first)) {
+        var first = first_statement(self.body);
+        if (compressor.option("dead_code") && (breaks(first) || first instanceof AST_Exit)) {
             var body = [];
             if (self.init instanceof AST_Statement) {
                 body.push(self.init);
@@ -4728,10 +4728,19 @@ merge(Compressor.prototype, {
                     body: self.init
                 }));
             }
-            if (self.condition) {
+            var retain = external_target(first) || first instanceof AST_Exit;
+            if (self.condition && retain) {
+                body.push(make_node(AST_If, self, {
+                    condition: self.condition,
+                    body: first,
+                    alternative: null
+                }));
+            } else if (self.condition) {
                 body.push(make_node(AST_SimpleStatement, self.condition, {
                     body: self.condition
                 }));
+            } else if (retain) {
+                body.push(first);
             }
             extract_declarations_from_unreachable_code(self.body, body);
             return make_node(AST_BlockStatement, self, {
@@ -4739,7 +4748,8 @@ merge(Compressor.prototype, {
             });
         }
         if (first instanceof AST_If) {
-            if (is_break(first.body)) {
+            var ab = first_statement(first.body);
+            if (breaks(ab)) {
                 if (self.condition) {
                     self.condition = make_node(AST_Binary, self.condition, {
                         left: self.condition,
@@ -4749,8 +4759,12 @@ merge(Compressor.prototype, {
                 } else {
                     self.condition = first.condition.negate(compressor);
                 }
-                drop_it(first.alternative);
-            } else if (is_break(first.alternative)) {
+                var body = as_statement_array(first.alternative);
+                extract_declarations_from_unreachable_code(first.body, body);
+                return drop_it(body);
+            }
+            ab = first_statement(first.alternative);
+            if (breaks(ab)) {
                 if (self.condition) {
                     self.condition = make_node(AST_Binary, self.condition, {
                         left: self.condition,
@@ -4760,18 +4774,27 @@ merge(Compressor.prototype, {
                 } else {
                     self.condition = first.condition;
                 }
-                drop_it(first.body);
+                var body = as_statement_array(first.body);
+                extract_declarations_from_unreachable_code(first.alternative, body);
+                return drop_it(body);
             }
         }
         return self;
 
-        function is_break(node) {
+        function first_statement(body) {
+            return body instanceof AST_BlockStatement ? body.body[0] : body;
+        }
+
+        function external_target(node) {
+            return compressor.loopcontrol_target(node) !== compressor.self();
+        }
+
+        function breaks(node) {
             return node instanceof AST_Break
-                && compressor.loopcontrol_target(node) === compressor.self();
+                || node instanceof AST_Continue && external_target(node);
         }
 
         function drop_it(rest) {
-            rest = as_statement_array(rest);
             if (self.body instanceof AST_BlockStatement) {
                 self.body = self.body.clone();
                 self.body.body = rest.concat(self.body.body.slice(1));
@@ -4781,7 +4804,7 @@ merge(Compressor.prototype, {
                     body: rest
                 }).transform(compressor);
             }
-            self = if_break_in_loop(self, compressor);
+            return if_break_in_loop(self, compressor);
         }
     }