fix corner case in ie8 (#3824)

fixes #3823

lib/compress.js

@@ -4906,20 +4906,39 @@ merge(Compressor.prototype, {
             var consequent = this.consequent.drop_side_effect_free(compressor);
             var alternative = this.alternative.drop_side_effect_free(compressor);
             if (consequent === this.consequent && alternative === this.alternative) return this;
-            if (!consequent) return alternative ? make_node(AST_Binary, this, {
+            var exprs;
-                operator: "||",
+            if (compressor.option("ie8")) {
-                left: this.condition,
+                exprs = [];
-                right: alternative
+                if (consequent instanceof AST_Function) {
-            }) : this.condition.drop_side_effect_free(compressor);
+                    exprs.push(consequent);
-            if (!alternative) return make_node(AST_Binary, this, {
+                    consequent = null;
-                operator: "&&",
+                }
-                left: this.condition,
+                if (alternative instanceof AST_Function) {
-                right: consequent
+                    exprs.push(alternative);
-            });
+                    alternative = null;
-            var node = this.clone();
+                }
-            node.consequent = consequent;
+            }
-            node.alternative = alternative;
+            var node;
-            return node;
+            if (!consequent) {
+                node = alternative ? make_node(AST_Binary, this, {
+                    operator: "||",
+                    left: this.condition,
+                    right: alternative
+                }) : this.condition.drop_side_effect_free(compressor);
+            } else if (!alternative) {
+                node = make_node(AST_Binary, this, {
+                    operator: "&&",
+                    left: this.condition,
+                    right: consequent
+                });
+            } else {
+                node = this.clone();
+                node.consequent = consequent;
+                node.alternative = alternative;
+            }
+            if (!compressor.option("ie8")) return node;
+            if (node) exprs.push(node);
+            return make_sequence(this, exprs);
         });
         def(AST_Constant, return_null);
         def(AST_Dot, function(compressor, first_in_statement) {

test/compress/ie8.js

@@ -2420,3 +2420,28 @@ issue_3750: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3823: {
+    options = {
+        ie8: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        for (var i = 0; i < 1; i++) {
+            var a = a ? function f() {
+                f;
+            } : 0;
+            console.log("PASS", typeof f);
+        }
+    }
+    expect: {
+        for (var i = 0; i < 1; i++) {
+            (function f() {
+                f;
+            });
+            console.log("PASS", typeof f);
+        }
+    }
+    expect_stdout: "PASS undefined"
+}