JVM, JVM IR: Don't optimize null-checks based on nullability information

Since Java interop allows us to circumvent the Kotlin type system we
cannot rely on nullability information.

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

@@ -3871,12 +3871,11 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
         Type type = expressionType(exp);
         StackValue argument = pregeneratedExpr != null ? pregeneratedExpr : gen(exp);
 
-        if (kotlinType == null || TypeUtils.isNullableType(kotlinType)) {
+        if (kotlinType == null ||
+            !AsmUtil.isPrimitive(type) && (TypeUtils.isNullableType(kotlinType) || !InlineClassesUtilsKt.isInlineClassType(kotlinType))) {
             return StackValue.compareWithNull(argument, (KtTokens.EQEQ == opToken || KtTokens.EQEQEQ == opToken) ? IFNONNULL : IFNULL);
         } else {
-            // If exp has a non-nullable type, the comparison is vacuous.
-            // For inline classes we cannot necessarily compare with null at all.
-            // In this case the code below is necessary for correctness, not just an optimization.
+            // If exp is an unboxed inline class value the comparison is vacuous
             return StackValue.operation(Type.BOOLEAN_TYPE, v -> {
                 argument.put(type, kotlinType, v);
                 AsmUtil.pop(v, type);

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/intrinsics/Equals.kt

@@ -17,7 +17,9 @@ import org.jetbrains.kotlin.codegen.intrinsics.IntrinsicMethods
 import org.jetbrains.kotlin.codegen.pseudoInsns.fakeAlwaysFalseIfeq
 import org.jetbrains.kotlin.codegen.pseudoInsns.fakeAlwaysTrueIfeq
 import org.jetbrains.kotlin.config.LanguageFeature
-import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.expressions.IrFunctionAccessExpression
+import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.types.classOrNull
 import org.jetbrains.kotlin.ir.types.isNullable
 import org.jetbrains.kotlin.ir.types.toKotlinType
 import org.jetbrains.kotlin.ir.util.isNullConst
@@ -46,8 +48,9 @@ class Equals(val operator: IElementType) : IntrinsicMethod() {
     override fun invoke(expression: IrFunctionAccessExpression, codegen: ExpressionCodegen, data: BlockInfo): PromisedValue? {
         val (a, b) = expression.receiverAndArgs()
         if (a.isNullConst() || b.isNullConst()) {
-            val value = if (a.isNullConst()) b.accept(codegen, data) else a.accept(codegen, data)
-            return if (a.type.isNullable() && b.type.isNullable())
+            val irValue = if (a.isNullConst()) b else a
+            val value = irValue.accept(codegen, data)
+            return if (!isPrimitive(value.type) && (irValue.type.classOrNull?.owner?.isInline != true || irValue.type.isNullable()))
                 BooleanNullCheck(value)
             else
                 BooleanConstantFalseCheck(value)

compiler/testData/codegen/box/platformTypes/unsafeNullCheck.kt

@@ -0,0 +1,18 @@
+// TARGET_BACKEND: JVM
+// FILE: Unsound.java
+
+import test.Wrap;
+
+public class Unsound {
+    public static <T> Wrap<T> get() {
+        return new Wrap<T>(null);
+    }
+}
+
+// FILE: 1.kt
+
+package test
+
+class Wrap<T>(val x: T)
+
+fun box(): String = if ((Unsound.get<String>() as Wrap<String>).x == null) "OK" else "Fail"

compiler/tests/org/jetbrains/kotlin/codegen/BlackBoxCodegenTestGenerated.java

@@ -17920,6 +17920,11 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/platformTypes"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("unsafeNullCheck.kt")
+        public void testUnsafeNullCheck() throws Exception {
+            runTest("compiler/testData/codegen/box/platformTypes/unsafeNullCheck.kt");
+        }
+
         @TestMetadata("compiler/testData/codegen/box/platformTypes/primitives")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -17920,6 +17920,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/platformTypes"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM, true);
         }
 
+        @TestMetadata("unsafeNullCheck.kt")
+        public void testUnsafeNullCheck() throws Exception {
+            runTest("compiler/testData/codegen/box/platformTypes/unsafeNullCheck.kt");
+        }
+
         @TestMetadata("compiler/testData/codegen/box/platformTypes/primitives")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)

compiler/tests/org/jetbrains/kotlin/codegen/ir/IrBlackBoxCodegenTestGenerated.java

@@ -16480,6 +16480,11 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/platformTypes"), Pattern.compile("^(.+)\\.kt$"), TargetBackend.JVM_IR, true);
         }
 
+        @TestMetadata("unsafeNullCheck.kt")
+        public void testUnsafeNullCheck() throws Exception {
+            runTest("compiler/testData/codegen/box/platformTypes/unsafeNullCheck.kt");
+        }
+
         @TestMetadata("compiler/testData/codegen/box/platformTypes/primitives")
         @TestDataPath("$PROJECT_ROOT")
         @RunWith(JUnit3RunnerWithInners.class)