Eliminate a set of warnings, mostly nullability ones

compiler/frontend/src/org/jetbrains/kotlin/psi/KtCodeFragment.kt

@@ -163,7 +163,7 @@ abstract class KtCodeFragment(
     }
 
     fun getContextContainingFile(): KtFile? {
-        return (getOriginalContext() as? KtElement)?.containingKtFile
+        return getOriginalContext()?.containingKtFile
     }
 
     fun getOriginalContext(): KtElement? {

compiler/frontend/src/org/jetbrains/kotlin/psi/KtEnumEntrySuperclassReferenceExpression.kt

@@ -40,7 +40,7 @@ class KtEnumEntrySuperclassReferenceExpression :
             get() = calcReferencedElement()!!
 
     private fun calcReferencedElement(): KtClass? {
-        val owner = this.getStrictParentOfType<KtEnumEntry>() as? KtEnumEntry
+        val owner = this.getStrictParentOfType<KtEnumEntry>()
         return owner?.parent?.parent as? KtClass
     }
 

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/ConstModifierChecker.kt

@@ -65,7 +65,7 @@ object ConstModifierChecker : SimpleDeclarationChecker {
             return Errors.CONST_VAL_WITH_DELEGATE.on(declaration.delegate!!).nonApplicable()
         }
 
-        if (descriptor is PropertyDescriptor && !descriptor.getter!!.isDefault) {
+        if (!descriptor.getter!!.isDefault) {
             return Errors.CONST_VAL_WITH_GETTER.on(declaration.getter!!).nonApplicable()
         }
 

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/LabelResolver.kt

@@ -90,6 +90,7 @@ object LabelResolver {
 
         if (parent is KtValueArgument) {
             // f ({}) or f(p = {}) or f (fun () {})
+            // NB: parent of KtElement is really nullable!!!
             val argList = parent.parent ?: return null
             val call = argList.parent
             if (call is KtCallExpression) {