enhance if_return (#3875)

lib/compress.js

@@ -2027,8 +2027,10 @@ merge(Compressor.prototype, {
 
         function handle_if_return(statements, compressor) {
             var self = compressor.self();
-            var multiple_if_returns = has_multiple_if_returns(statements);
+            var parent = compressor.parent();
             var in_lambda = self instanceof AST_Lambda;
+            var in_iife = in_lambda && parent && parent.TYPE == "Call";
+            var multiple_if_returns = has_multiple_if_returns(statements);
             for (var i = statements.length; --i >= 0;) {
                 var stat = statements[i];
                 var j = next_index(i);
@@ -2156,7 +2158,7 @@ merge(Compressor.prototype, {
                     // the example code.
                     var prev = statements[prev_index(i)];
                     if (compressor.option("sequences") && in_lambda && !stat.alternative
-                        && prev instanceof AST_If && prev.body instanceof AST_Return
+                        && (!prev && in_iife || prev instanceof AST_If && prev.body instanceof AST_Return)
                         && next_index(j) == statements.length && next instanceof AST_SimpleStatement) {
                         CHANGED = true;
                         stat = stat.clone();

test/compress/if_return.js

@@ -573,3 +573,24 @@ issue_3600: {
     }
     expect_stdout: "1"
 }
+
+iife_if_return_simple: {
+    options = {
+        conditionals: true,
+        if_return: true,
+        inline: true,
+        sequences: true,
+        side_effects: true,
+    }
+    input: {
+        (function() {
+            if (console)
+                return console.log("PASS");
+            console.log("FAIL");
+        })();
+    }
+    expect: {
+        console ? console.log("PASS") : console.log("FAIL");
+    }
+    expect_stdout: "PASS"
+}