improve `AST_For.init` & `AST_Switch.expression` compression (#2546)

1 files changed, 12 insertions, 5 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 8b2951d8..dfee94fc 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1436,7 +1436,7 @@ merge(Compressor.prototype, {
                         if (!abort) {
                             if (stat.init) stat.init = cons_seq(stat.init);
                             else {
-                                stat.init = prev.body.drop_side_effect_free(compressor);
+                                stat.init = prev.body;
                                 n--;
                             }
                         }
@@ -3105,6 +3105,9 @@ merge(Compressor.prototype, {
 
     OPT(AST_For, function(self, compressor){
         if (!compressor.option("loops")) return self;
+        if (compressor.option("side_effects") && self.init) {
+            self.init = self.init.drop_side_effect_free(compressor);
+        }
         if (self.condition) {
             var cond = self.condition.evaluate(compressor);
             if (!(cond instanceof AST_Node)) {
@@ -3286,11 +3289,15 @@ merge(Compressor.prototype, {
         if (!compressor.option("switches")) return self;
         var branch;
         var value = self.expression.evaluate(compressor);
-        if (value !== self.expression) {
-            var expression = make_node_from_constant(value, self.expression).transform(compressor);
-            self.expression = best_of_expression(expression, self.expression);
+        if (!(value instanceof AST_Node)) {
+            var orig = self.expression;
+            self.expression = make_node_from_constant(value, orig);
+            self.expression = best_of_expression(self.expression.transform(compressor), orig);
         }
         if (!compressor.option("dead_code")) return self;
+        if (value instanceof AST_Node) {
+            value = self.expression.tail_node().evaluate(compressor);
+        }
         var decl = [];
         var body = [];
         var default_branch;
@@ -3303,7 +3310,7 @@ merge(Compressor.prototype, {
                 } else {
                     eliminate_branch(branch, body[body.length - 1]);
                 }
-            } else if (value !== self.expression) {
+            } else if (!(value instanceof AST_Node)) {
                 var exp = branch.expression.evaluate(compressor);
                 if (exp === value) {
                     exact_match = branch;