1 files changed, 62 insertions, 21 deletions
diff --git a/lib/compress.js b/lib/compress.js
index c9892ce2..8bc8b37e 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -5916,28 +5916,57 @@ merge(Compressor.prototype, {
         }
         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) {
-                if (has_break
-                    || node instanceof AST_Lambda
-                    || node instanceof AST_SimpleStatement) return true;
-                if (is_break(node, tw)) has_break = true;
+        if (compressor.option("conditionals")) switch (body.length) {
+          case 1:
+            if (!no_break(self)) break;
+            var exp = body[0].expression;
+            var statements = body[0].body.slice();
+            if (body[0] !== default_branch && body[0] !== exact_match) return make_node(AST_If, self, {
+                condition: make_node(AST_Binary, self, {
+                    operator: "===",
+                    left: self.expression,
+                    right: exp,
+                }),
+                body: make_node(AST_BlockStatement, self, {
+                    body: statements,
+                }),
+                alternative: null,
+            }).optimize(compressor);
+            if (exp) statements.unshift(make_node(AST_SimpleStatement, exp, {
+                body: exp,
+            }));
+            statements.unshift(make_node(AST_SimpleStatement, self.expression, {
+                body:self.expression,
+            }));
+            return make_node(AST_BlockStatement, self, {
+                body: statements,
+            }).optimize(compressor);
+          case 2:
+            if (!member(default_branch, body)) break;
+            var statements = body[0].body.slice();
+            var exclusive = statements.length && is_break(statements[statements.length - 1], compressor);
+            if (exclusive) statements.pop();
+            if (!all(statements, no_break)) break;
+            var alternative = body[1].body.length && make_node(AST_BlockStatement, body[1], body[1]);
+            var node = make_node(AST_If, self, {
+                condition: make_node(AST_Binary, self, body[0] === default_branch ? {
+                    operator: "!==",
+                    left: self.expression,
+                    right: body[1].expression,
+                } : {
+                    operator: "===",
+                    left: self.expression,
+                    right: body[0].expression,
+                }),
+                body: make_node(AST_BlockStatement, body[0], {
+                    body: statements,
+                }),
+                alternative: exclusive && alternative || null,
             });
-            self.walk(tw);
-            if (!has_break) {
-                var statements = body[0].body.slice();
-                var exp = body[0].expression;
-                if (exp) statements.unshift(make_node(AST_SimpleStatement, exp, {
-                    body: exp
-                }));
-                statements.unshift(make_node(AST_SimpleStatement, self.expression, {
-                    body:self.expression
-                }));
-                return make_node(AST_BlockStatement, self, {
-                    body: statements
-                }).optimize(compressor);
-            }
+            if (!exclusive && alternative) node = make_node(AST_BlockStatement, self, {
+                body: [ node, alternative ],
+            });
+            return node.optimize(compressor);
         }
         return self;
 
@@ -5945,6 +5974,18 @@ merge(Compressor.prototype, {
             return node instanceof AST_Break && tw.loopcontrol_target(node) === self;
         }
 
+        function no_break(node) {
+            var found = false;
+            var tw = new TreeWalker(function(node) {
+                if (found
+                    || node instanceof AST_Lambda
+                    || node instanceof AST_SimpleStatement) return true;
+                if (is_break(node, tw)) found = true;
+            });
+            node.walk(tw);
+            return !found;
+        }
+
         function eliminate_branch(branch, prev) {
             if (prev && !aborts(prev)) {
                 prev.body = prev.body.concat(branch.body);