JS: when both clauses of if become empty during optimization, remove if entirely. Make condition and then clause of JsIf non-nullable. Fix #KT-13912

js/js.translator/testData/js-optimizer/redundant-label-removal/emptyIfConditionPreserved.optimized.js

@@ -0,0 +1,17 @@
+var global = "";
+
+function id(value) {
+    global += value + ";";
+    return value;
+}
+
+function test(x) {
+    id(x);
+    id(x + 1);
+}
+
+function box() {
+    test(23);
+    if (global != "23;24;") return "fail";
+    return "OK";
+}

js/js.translator/testData/js-optimizer/redundant-label-removal/emptyIfConditionPreserved.original.js

@@ -0,0 +1,23 @@
+var global = "";
+
+function id(value) {
+    global += value + ";";
+    return value;
+}
+
+function test(x) {
+    $outer: {
+        if (id(x) + id(x + 1) > 0) {
+            break $outer;
+        }
+        else {
+            break $outer;
+        }
+    }
+}
+
+function box() {
+    test(23);
+    if (global != "23;24;") return "fail";
+    return "OK";
+}

js/js.translator/testData/js-optimizer/redundant-label-removal/ifWithEmptyThenAndNoElse.optimized.js

@@ -0,0 +1,7 @@
+function test(x) {
+    return "OK";
+}
+
+function box() {
+    return test(23);
+}

js/js.translator/testData/js-optimizer/redundant-label-removal/ifWithEmptyThenAndNoElse.original.js

@@ -0,0 +1,12 @@
+function test(x) {
+    $outer: {
+        if (x > 10) {
+            break $outer;
+        }
+    }
+    return "OK";
+}
+
+function box() {
+    return test(23);
+}