fix typeof side effects (#1696)

`statement_to_expression()` drops `typeof` even if it operates on undeclared variables.

Since we now have `drop_side_effect_free()`, replace and remove this deprecated functionality.

lib/compress.js

@@ -482,15 +482,6 @@ merge(Compressor.prototype, {
         return x;
     };
 
-    var readOnlyPrefix = makePredicate("! ~ + - void typeof");
-    function statement_to_expression(stat) {
-        if (stat.body instanceof AST_UnaryPrefix && readOnlyPrefix(stat.body.operator)) {
-            return stat.body.expression;
-        } else {
-            return stat.body;
-        }
-    }
-
     function is_iife_call(node) {
         if (node instanceof AST_Call && !(node instanceof AST_New)) {
             return node.expression instanceof AST_Function || is_iife_call(node.expression);
@@ -984,10 +975,10 @@ merge(Compressor.prototype, {
             };
             statements.forEach(function(stat){
                 if (stat instanceof AST_SimpleStatement) {
-                    if (seqLength(seq) >= compressor.sequences_limit) {
-                        push_seq();
-                    }
-                    seq.push(seq.length > 0 ? statement_to_expression(stat) : stat.body);
+                    if (seqLength(seq) >= compressor.sequences_limit) push_seq();
+                    var body = stat.body;
+                    if (seq.length > 0) body = body.drop_side_effect_free(compressor);
+                    if (body) seq.push(body);
                 } else {
                     push_seq();
                     ret.push(stat);
@@ -1036,7 +1027,7 @@ merge(Compressor.prototype, {
                                 stat.init = cons_seq(stat.init);
                             }
                             else if (!stat.init) {
-                                stat.init = statement_to_expression(prev);
+                                stat.init = prev.body.drop_side_effect_free(compressor);
                                 ret.pop();
                             }
                         } catch(ex) {
@@ -2170,6 +2161,7 @@ merge(Compressor.prototype, {
             switch (this.operator) {
               case "&&":
               case "||":
+                if (right === this.right) return this;
                 var node = this.clone();
                 node.right = right;
                 return node;
@@ -2423,8 +2415,8 @@ merge(Compressor.prototype, {
             return make_node(AST_SimpleStatement, self, {
                 body: make_node(AST_Conditional, self, {
                     condition   : self.condition,
-                    consequent  : statement_to_expression(self.body),
-                    alternative : statement_to_expression(self.alternative)
+                    consequent  : self.body.body,
+                    alternative : self.alternative.body
                 })
             }).optimize(compressor);
         }
@@ -2440,25 +2432,24 @@ merge(Compressor.prototype, {
                 body: make_node(AST_Binary, self, {
                     operator : "||",
                     left     : negated,
-                    right    : statement_to_expression(self.body)
+                    right    : self.body.body
                 })
             }).optimize(compressor);
             return make_node(AST_SimpleStatement, self, {
                 body: make_node(AST_Binary, self, {
                     operator : "&&",
                     left     : self.condition,
-                    right    : statement_to_expression(self.body)
+                    right    : self.body.body
                 })
             }).optimize(compressor);
         }
         if (self.body instanceof AST_EmptyStatement
-            && self.alternative
             && self.alternative instanceof AST_SimpleStatement) {
             return make_node(AST_SimpleStatement, self, {
                 body: make_node(AST_Binary, self, {
                     operator : "||",
                     left     : self.condition,
-                    right    : statement_to_expression(self.alternative)
+                    right    : self.alternative.body
                 })
             }).optimize(compressor);
         }

test/compress/negate-iife.js

@@ -353,8 +353,9 @@ issue_1254_negate_iife_nested: {
 
 issue_1288: {
     options = {
-        negate_iife: true,
         conditionals: true,
+        negate_iife: true,
+        side_effects: false,
     };
     input: {
         if (w) ;
@@ -374,11 +375,11 @@ issue_1288: {
             })(0);
     }
     expect: {
-        w || function f() {}();
-        x || function() {
+        w || !function f() {}();
+        x || !function() {
             x = {};
         }();
-        y ? function() {}() : function(z) {
+        y ? !function() {}() : !function(z) {
             return z;
         }(0);
     }

test/compress/switch.js

@@ -579,3 +579,17 @@ issue_1690_2: {
     }
     expect_stdout: "PASS"
 }
+
+if_switch_typeof: {
+    options = {
+        conditionals: true,
+        dead_code: true,
+        side_effects: true,
+    }
+    input: {
+        if (a) switch(typeof b) {}
+    }
+    expect: {
+        a;
+    }
+}