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

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;

test/compress/loops.js

@@ -452,3 +452,19 @@ in_parenthesis_2: {
     }
     expect_exact: 'for(function(){"foo"in{}};0;);'
 }
+
+init_side_effects: {
+    options = {
+        loops: true,
+        side_effects: true,
+    };
+    input: {
+        for (function() {}(), i = 0; i < 5; i++) console.log(i);
+        for (function() {}(); i < 10; i++) console.log(i);
+    }
+    expect: {
+        for (i = 0; i < 5; i++) console.log(i);
+        for (; i < 10; i++) console.log(i);
+    }
+    expect_stdout: true
+}

test/compress/sequences.js

@@ -252,13 +252,12 @@ negate_iife_for: {
     input: {
         (function() {})();
         for (i = 0; i < 5; i++) console.log(i);
-
         (function() {})();
-        for (; i < 5; i++) console.log(i);
+        for (; i < 10; i++) console.log(i);
     }
     expect: {
         for (!function() {}(), i = 0; i < 5; i++) console.log(i);
-        for (function() {}(); i < 5; i++) console.log(i);
+        for (!function() {}(); i < 10; i++) console.log(i);
     }
     expect_stdout: true
 }

test/compress/switch.js

@@ -817,3 +817,23 @@ issue_1758: {
     }
     expect_stdout: "0 3"
 }
+
+issue_2535: {
+    options = {
+        evaluate: true,
+        dead_code: true,
+        switches: true,
+    }
+    input: {
+        switch(w(), 42) {
+            case 13: x();
+            case 42: y();
+            default: z();
+        }
+    }
+    expect: {
+        w(), 42;
+        y();
+        z();
+    }
+}