Add a fallback flag -Xno-unified-null-checks for KT-22275

#KT-41482 Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java

@@ -5051,7 +5051,9 @@ The "returned" value of try expression with no finally is either the last expres
                 return Unit.INSTANCE;
             }
 
-            CodegenUtilKt.generateAsCast(v, rightKotlinType, boxedRightType, safeAs, state.getLanguageVersionSettings());
+            CodegenUtilKt.generateAsCast(
+                    v, rightKotlinType, boxedRightType, safeAs, state.getLanguageVersionSettings(), state.getUnifiedNullChecks()
+            );
 
             return Unit.INSTANCE;
         });

compiler/backend/src/org/jetbrains/kotlin/codegen/codegenUtil.kt

@@ -98,11 +98,12 @@ fun generateAsCast(
     kotlinType: KotlinType,
     asmType: Type,
     isSafe: Boolean,
-    languageVersionSettings: LanguageVersionSettings
+    languageVersionSettings: LanguageVersionSettings,
+    unifiedNullChecks: Boolean,
 ) {
     if (!isSafe) {
         if (!TypeUtils.isNullableType(kotlinType)) {
-            generateNullCheckForNonSafeAs(v, kotlinType, languageVersionSettings)
+            generateNullCheckForNonSafeAs(v, kotlinType, unifiedNullChecks)
         }
     } else {
         with(v) {
@@ -122,15 +123,13 @@ fun generateAsCast(
 private fun generateNullCheckForNonSafeAs(
     v: InstructionAdapter,
     type: KotlinType,
-    languageVersionSettings: LanguageVersionSettings
+    unifiedNullChecks: Boolean,
 ) {
     with(v) {
         dup()
         val nonnull = Label()
         ifnonnull(nonnull)
-        val exceptionClass =
-            if (languageVersionSettings.apiVersion >= ApiVersion.KOTLIN_1_4) "java/lang/NullPointerException"
-            else "kotlin/TypeCastException"
+        val exceptionClass = if (unifiedNullChecks) "java/lang/NullPointerException" else "kotlin/TypeCastException"
         AsmUtil.genThrow(
             v,
             exceptionClass,

compiler/backend/src/org/jetbrains/kotlin/codegen/inline/PsiInlineCodegen.kt

@@ -41,7 +41,10 @@ class PsiInlineCodegen(
     private val actualDispatchReceiver: Type = methodOwner
 ) : InlineCodegen<ExpressionCodegen>(
     codegen, state, function, methodOwner, signature, typeParameterMappings, sourceCompiler,
-    ReifiedTypeInliner(typeParameterMappings, PsiInlineIntrinsicsSupport(state), codegen.typeSystem, state.languageVersionSettings),
+    ReifiedTypeInliner(
+        typeParameterMappings, PsiInlineIntrinsicsSupport(state), codegen.typeSystem,
+        state.languageVersionSettings, state.unifiedNullChecks
+    ),
 ), CallGenerator {
     override fun generateAssertFieldIfNeeded(info: RootInliningContext) {
         if (info.generateAssertField) {

compiler/backend/src/org/jetbrains/kotlin/codegen/inline/ReifiedTypeInliner.kt

@@ -53,7 +53,8 @@ class ReifiedTypeInliner<KT : KotlinTypeMarker>(
     private val parametersMapping: TypeParameterMappings<KT>?,
     private val intrinsicsSupport: IntrinsicsSupport<KT>,
     private val typeSystem: TypeSystemCommonBackendContext,
-    private val languageVersionSettings: LanguageVersionSettings
+    private val languageVersionSettings: LanguageVersionSettings,
+    private val unifiedNullChecks: Boolean,
 ) {
     enum class OperationKind {
         NEW_ARRAY, AS, SAFE_AS, IS, JAVA_CLASS, ENUM_REIFIED, TYPE_OF;
@@ -222,7 +223,7 @@ class ReifiedTypeInliner<KT : KotlinTypeMarker>(
         if (stubCheckcast !is TypeInsnNode) return false
 
         val newMethodNode = MethodNode(Opcodes.API_VERSION)
-        generateAsCast(InstructionAdapter(newMethodNode), kotlinType, asmType, safe, languageVersionSettings)
+        generateAsCast(InstructionAdapter(newMethodNode), kotlinType, asmType, safe, languageVersionSettings, unifiedNullChecks)
 
         instructions.insert(insn, newMethodNode.instructions)
         // Keep stubCheckcast to avoid VerifyErrors on 1.8+ bytecode,

compiler/backend/src/org/jetbrains/kotlin/codegen/state/GenerationState.kt

@@ -249,7 +249,9 @@ class GenerationState private constructor(
     val assertionsMode: JVMAssertionsMode = configuration.get(JVMConfigurationKeys.ASSERTIONS_MODE, JVMAssertionsMode.DEFAULT)
     val isInlineDisabled: Boolean = configuration.getBoolean(CommonConfigurationKeys.DISABLE_INLINE)
     val useTypeTableInSerializer: Boolean = configuration.getBoolean(JVMConfigurationKeys.USE_TYPE_TABLE)
-    val unifiedNullChecks: Boolean = languageVersionSettings.apiVersion >= ApiVersion.KOTLIN_1_4
+    val unifiedNullChecks: Boolean =
+        languageVersionSettings.apiVersion >= ApiVersion.KOTLIN_1_4 &&
+                !configuration.getBoolean(JVMConfigurationKeys.NO_UNIFIED_NULL_CHECKS)
     val functionsWithInlineClassReturnTypesMangled: Boolean =
         languageVersionSettings.supportsFeature(LanguageFeature.MangleClassMembersReturningInlineClasses)