JVM IR: Avoid unnecessary CHECKCASTs in enum classes

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -539,7 +539,17 @@ class ExpressionCodegen(
             ownerType.internalName
         } ?: typeMapper.mapClass(callee.parentAsClass).internalName
         return if (expression is IrSetField) {
-            expression.value.accept(this, data).materializeAt(fieldType, callee.type)
+            val value = expression.value.accept(this, data)
+
+            // We only initialize enum entries with a subtype of `fieldType` and can avoid the CHECKCAST.
+            // This is important for some tools which analyze bytecode for enum classes by looking at the
+            // initializer of the $VALUES field.
+            if (callee.origin == IrDeclarationOrigin.FIELD_FOR_ENUM_ENTRY) {
+                value.materialize()
+            } else {
+                value.materializeAt(fieldType, callee.type)
+            }
+
             when {
                 isStatic -> mv.putstatic(ownerName, fieldName, fieldType.descriptor)
                 else -> mv.putfield(ownerName, fieldName, fieldType.descriptor)

compiler/testData/codegen/bytecodeText/enum/enumCheckcasts.kt

@@ -0,0 +1,12 @@
+enum class Foo {
+    A, B, C { override fun result() = "OK" };
+    open fun result() = "Fail"
+}
+
+// JVM_TEMPLATES:
+// There are two CHECKCASTs, one in Foo.valueOf and one in Foo.values
+// 2 CHECKCAST
+
+// JVM_IR_TEMPLATES:
+// There should be only one CHECKCAST in Foo.valueOf
+// 1 CHECKCAST

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

@@ -1855,6 +1855,11 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/bytecodeText/enum"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JVM, true);
         }
 
+        @TestMetadata("enumCheckcasts.kt")
+        public void testEnumCheckcasts() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/enum/enumCheckcasts.kt");
+        }
+
         @TestMetadata("kt18731.kt")
         public void testKt18731() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/enum/kt18731.kt");

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

@@ -1810,6 +1810,11 @@ public class IrBytecodeTextTestGenerated extends AbstractIrBytecodeTextTest {
             KotlinTestUtils.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/bytecodeText/enum"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JVM_IR, true);
         }
 
+        @TestMetadata("enumCheckcasts.kt")
+        public void testEnumCheckcasts() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/enum/enumCheckcasts.kt");
+        }
+
         @TestMetadata("kt18731.kt")
         public void testKt18731() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/enum/kt18731.kt");