enhance if_return (#5518)

test/compress/if_return.js

@@ -850,3 +850,116 @@ issue_866_2: {
         })();
     }
 }
+
+identical_returns_1: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        console.log(function() {
+            if (console.log("foo"))
+                return 42;
+            else
+                while (console.log("bar"));
+            return 42;
+        }());
+    }
+    expect: {
+        console.log(function() {
+            if (!console.log("foo"))
+                while (console.log("bar"));
+            return 42;
+        }());
+    }
+    expect_stdout: [
+        "foo",
+        "bar",
+        "42",
+    ]
+}
+
+identical_returns_2: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        console.log(function() {
+            if (console.log("foo"))
+                while (console.log("FAIL"));
+            else
+                return "bar";
+            return "bar";
+        }());
+    }
+    expect: {
+        console.log(function() {
+            if (console.log("foo"))
+                while (console.log("FAIL"));
+            return "bar";
+        }());
+    }
+    expect_stdout: [
+        "foo",
+        "bar",
+    ]
+}
+
+identical_returns_3: {
+    options = {
+        if_return: true,
+    }
+    input: {
+        function f(a) {
+            if (a)
+                return 42;
+            if (a)
+                return;
+            return 42;
+        }
+        if (f(console))
+            console.log("PASS");
+    }
+    expect: {
+        function f(a) {
+            if (a)
+                return 42;
+            if (a)
+                ;
+            else
+                return 42;
+        }
+        if (f(console))
+            console.log("PASS");
+    }
+    expect_stdout: "PASS"
+}
+
+issue_4374: {
+    options = {
+        booleans: true,
+        conditionals: true,
+        if_return: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            console.log(f(console));
+            function f(a) {
+                if (console) return 0;
+                if (a) return 1;
+                return 0;
+            }
+        })();
+    }
+    expect: {
+        (function() {
+            console.log(function(a) {
+                return !console && a ? 1 : 0;
+            }(console));
+        })();
+    }
+    expect_stdout: "0"
+}

test/compress/let.js

@@ -892,6 +892,40 @@ if_return_2: {
     node_version: ">=4"
 }
 
+if_return_3: {
+    options = {
+        if_return: true,
+    }
+    input: {
+        "use strict";
+        var a = "PASS";
+        function f(b) {
+            if (console) {
+                let b = a;
+                return b;
+            } else
+                while (console.log("FAIL 1"));
+            return b;
+        }
+        console.log(f("FAIL 2"));
+    }
+    expect: {
+        "use strict";
+        var a = "PASS";
+        function f(b) {
+            if (console) {
+                let b = a;
+                return b;
+            } else
+                while (console.log("FAIL 1"));
+            return b;
+        }
+        console.log(f("FAIL 2"));
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
 do_if_continue_1: {
     options = {
         if_return: true,

test/compress/transform.js

@@ -127,7 +127,7 @@ if_return: {
                 if (w) {
                     if (y) return;
                 } else if (z) return;
-                return x == y || (x && w(), y && z()), !0;
+                return x != y && (x && w(), y && z()), !0;
             }
         }
     }