Make CHECKCAST Object not break tail-call optimization

Since CHECKCAST Object does nothing for return value of suspend
function - the function returns references only, this is safe.
 #KT-49157 Fixed

compiler/backend/src/org/jetbrains/kotlin/codegen/coroutines/TailCallOptimization.kt

@@ -17,10 +17,7 @@ import org.jetbrains.kotlin.utils.sure
 import org.jetbrains.org.objectweb.asm.Label
 import org.jetbrains.org.objectweb.asm.Opcodes
 import org.jetbrains.org.objectweb.asm.Type
-import org.jetbrains.org.objectweb.asm.tree.AbstractInsnNode
-import org.jetbrains.org.objectweb.asm.tree.LineNumberNode
-import org.jetbrains.org.objectweb.asm.tree.MethodNode
-import org.jetbrains.org.objectweb.asm.tree.VarInsnNode
+import org.jetbrains.org.objectweb.asm.tree.*
 import org.jetbrains.org.objectweb.asm.tree.analysis.BasicInterpreter
 import org.jetbrains.org.objectweb.asm.tree.analysis.BasicValue
 import org.jetbrains.org.objectweb.asm.tree.analysis.Frame
@@ -155,7 +152,7 @@ internal class MethodNodeExaminer(
             }
 
             if (!insn.isMeaningful || insn.opcode in SAFE_OPCODES || insn.isInvisibleInDebugVarInsn(methodNode) || isInlineMarker(insn)
-                || insn.isSafeUnitInstance() || insn.isAreturnAfterSafeUnitInstance()
+                || insn.isSafeUnitInstance() || insn.isAreturnAfterSafeUnitInstance() || insn.isCheckcastObject()
             ) {
                 setOf()
             } else null
@@ -187,6 +184,9 @@ internal class MethodNodeExaminer(
     }
 }
 
+private fun AbstractInsnNode.isCheckcastObject(): Boolean =
+    opcode == Opcodes.CHECKCAST && (this as TypeInsnNode).desc == AsmTypes.OBJECT_TYPE.internalName
+
 private fun AbstractInsnNode?.isInvisibleInDebugVarInsn(methodNode: MethodNode): Boolean {
     val insns = methodNode.instructions
     val index = insns.indexOf(this)
@@ -225,6 +225,11 @@ private class TcoInterpreter(private val suspensionPoints: List<SuspensionPoint>
     }
 
     override fun unaryOperation(insn: AbstractInsnNode, value: BasicValue?): BasicValue? {
+        // Assume, that CHECKCAST Object does not break tail-call optimization
+        // TODO: Investigate, whether any CHECKCAST is safe in terms of tail-call optimization
+        if (value is FromSuspensionPointValue && insn.isCheckcastObject()) {
+            return value
+        }
         return super.unaryOperation(insn, value).convert(insn)
     }
 

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirBlackBoxCodegenTestGenerated.java

@@ -12241,6 +12241,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
                 runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/crossinline.kt");
             }
 
+            @Test
+            @TestMetadata("deferredAwaitSuspendImpl.kt")
+            public void testDeferredAwaitSuspendImpl() throws Exception {
+                runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/deferredAwaitSuspendImpl.kt");
+            }
+
             @Test
             @TestMetadata("inlineWithStateMachine.kt")
             public void testInlineWithStateMachine() throws Exception {

compiler/testData/codegen/box/coroutines/tailCallOptimizations/deferredAwaitSuspendImpl.kt

@@ -0,0 +1,32 @@
+// TARGET_BACKEND: JVM
+// FULL_JDK
+// WITH_RUNTIME
+// WITH_COROUTINES
+// CHECK_TAIL_CALL_OPTIMIZATION
+import helpers.*
+import kotlin.coroutines.*
+import kotlin.coroutines.intrinsics.*
+
+suspend fun awaitInternal(): Any? = TailCallOptimizationChecker.saveStackTrace()
+
+interface Deferred<out T> {
+    suspend fun await(): T
+}
+
+open class DeferredCoroutine<T> : Deferred<T> {
+    override suspend fun await(): T = awaitInternal() as T
+}
+
+fun builder(c: suspend () -> Unit) {
+    c.startCoroutine(Continuation(EmptyCoroutineContext) {
+        it.getOrThrow()
+    })
+}
+
+fun box(): String {
+    builder {
+        DeferredCoroutine<String>().await()
+    }
+    TailCallOptimizationChecker.checkNoStateMachineIn("await\$suspendImpl")
+    return "OK"
+}

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java

@@ -12163,6 +12163,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                 runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/crossinline.kt");
             }
 
+            @Test
+            @TestMetadata("deferredAwaitSuspendImpl.kt")
+            public void testDeferredAwaitSuspendImpl() throws Exception {
+                runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/deferredAwaitSuspendImpl.kt");
+            }
+
             @Test
             @TestMetadata("inlineWithStateMachine.kt")
             public void testInlineWithStateMachine() throws Exception {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java

@@ -12241,6 +12241,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                 runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/crossinline.kt");
             }
 
+            @Test
+            @TestMetadata("deferredAwaitSuspendImpl.kt")
+            public void testDeferredAwaitSuspendImpl() throws Exception {
+                runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/deferredAwaitSuspendImpl.kt");
+            }
+
             @Test
             @TestMetadata("inlineWithStateMachine.kt")
             public void testInlineWithStateMachine() throws Exception {

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

@@ -9784,6 +9784,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                 runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/crossinline.kt");
             }
 
+            @TestMetadata("deferredAwaitSuspendImpl.kt")
+            public void testDeferredAwaitSuspendImpl() throws Exception {
+                runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/deferredAwaitSuspendImpl.kt");
+            }
+
             @TestMetadata("inlineWithStateMachine.kt")
             public void testInlineWithStateMachine() throws Exception {
                 runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/inlineWithStateMachine.kt");