Loosen tail-call optimization check for functions returning Unit

Do not check, that all Unit predecessors are POPs. This is safe for the
same reason, as it is safe to allow some of ARETURN sources not be
suspension point results.
To elaborate, before Unit, the stack is empty. This is because if there
are multiple paths to Unit and at least one of them comes from POP after
suspension point (we are interested in this case only - otherwise, the
call is not tail-call), in path from said POP the stack is empty, since
after suspension point the stack contains only one element. Thus, the
stack in other paths leading to Unit has to be empty, otherwise, merge
operation is not possible and ASM will report error during analysis.
Since the stack is empty in all paths, we can hoist Unit and following
ARETURN to predecessors, effectively turning path from suspension point
to tail-call.

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

@@ -39,7 +39,6 @@ internal class MethodNodeExaminer(
     private val popsBeforeSafeUnitInstances = mutableSetOf<AbstractInsnNode>()
     private val areturnsAfterSafeUnitInstances = mutableSetOf<AbstractInsnNode>()
     private val meaningfulSuccessorsCache = hashMapOf<AbstractInsnNode, List<AbstractInsnNode>>()
-    private val meaningfulPredecessorsCache = hashMapOf<AbstractInsnNode, List<AbstractInsnNode>>()
 
     init {
         if (!disableTailCallOptimizationForFunctionReturningUnit) {
@@ -52,10 +51,8 @@ internal class MethodNodeExaminer(
             for (pop in popsBeforeUnitInstances) {
                 val units = pop.meaningfulSuccessors()
                 val allUnitsAreSafe = units.all { unit ->
-                    // check no other predecessor exists
+                    // check they have only returns among successors
-                    unit.meaningfulPredecessors().all { it in popsBeforeUnitInstances } &&
+                    unit.meaningfulSuccessors().all { it.opcode == Opcodes.ARETURN }
-                            // check they have only returns among successors
-                            unit.meaningfulSuccessors().all { it.opcode == Opcodes.ARETURN }
                 }
                 if (!allUnitsAreSafe) continue
                 // save them all to the properties
@@ -74,35 +71,22 @@ internal class MethodNodeExaminer(
     private fun AbstractInsnNode.isAreturnAfterSafeUnitInstance(): Boolean = this in areturnsAfterSafeUnitInstances
 
     private fun AbstractInsnNode.meaningfulSuccessors(): List<AbstractInsnNode> = meaningfulSuccessorsCache.getOrPut(this) {
-        meaningfulSuccessorsOrPredecessors(true)
-    }
-
-    private fun AbstractInsnNode.meaningfulPredecessors(): List<AbstractInsnNode> = meaningfulPredecessorsCache.getOrPut(this) {
-        meaningfulSuccessorsOrPredecessors(false)
-    }
-
-    private fun AbstractInsnNode.meaningfulSuccessorsOrPredecessors(isSuccessors: Boolean): List<AbstractInsnNode> {
         fun AbstractInsnNode.isMeaningful() = isMeaningful && opcode != Opcodes.NOP && opcode != Opcodes.GOTO && this !is LineNumberNode
 
-        fun AbstractInsnNode.getIndices() =
-            if (isSuccessors) controlFlowGraph.getSuccessorsIndices(this)
-            else controlFlowGraph.getPredecessorsIndices(this)
-
         val visited = mutableSetOf<AbstractInsnNode>()
         fun dfs(insn: AbstractInsnNode) {
             if (insn in visited) return
             visited += insn
             if (!insn.isMeaningful()) {
-                for (succIndex in insn.getIndices()) {
+                for (succIndex in controlFlowGraph.getSuccessorsIndices(insn)) {
                     dfs(methodNode.instructions[succIndex])
                 }
             }
         }
-
+        for (succIndex in controlFlowGraph.getSuccessorsIndices(this)) {
-        for (succIndex in getIndices()) {
             dfs(methodNode.instructions[succIndex])
         }
-        return visited.filter { it.isMeaningful() }
+        visited.filter { it.isMeaningful() }
     }
 
     fun replacePopsBeforeSafeUnitInstancesWithCoroutineSuspendedChecks() {

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

@@ -12144,6 +12144,12 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
                     runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/functionReference.kt");
                 }
 
+                @Test
+                @TestMetadata("inline.kt")
+                public void testInline() throws Exception {
+                    runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/inline.kt");
+                }
+
                 @Test
                 @TestMetadata("override.kt")
                 public void testOverride() throws Exception {

compiler/testData/codegen/box/coroutines/tailCallOptimizations/crossinline.txt

@@ -14,7 +14,6 @@ public final class CrossinlineKt$box$1$filter$$inlined$source$1$1 {
 }
 
 @kotlin.Metadata
-@kotlin.coroutines.jvm.internal.DebugMetadata
 public final class CrossinlineKt$box$1$filter$$inlined$source$1$lambda$1$1 {
     enclosing method CrossinlineKt$box$1$filter$$inlined$source$1$lambda$1.send(Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
     field label: int
@@ -96,19 +95,6 @@ public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$1 {
     public final @org.jetbrains.annotations.Nullable method invokeSuspend(@org.jetbrains.annotations.NotNull p0: java.lang.Object): java.lang.Object
 }
 
-@kotlin.Metadata
-@kotlin.coroutines.jvm.internal.DebugMetadata
-public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2$1 {
-    enclosing method CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2.send(Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
-    field label: int
-    synthetic field result: java.lang.Object
-    synthetic final field this$0: CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2
-    inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2
-    inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2$1
-    public method <init>(p0: CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2, p1: kotlin.coroutines.Continuation): void
-    public final @org.jetbrains.annotations.Nullable method invokeSuspend(@org.jetbrains.annotations.NotNull p0: java.lang.Object): java.lang.Object
-}
-
 @kotlin.Metadata
 public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2 {
     // source: 'crossinline.kt'
@@ -116,7 +102,6 @@ public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2 {
     synthetic final field $this_source$inlined: Sink
     synthetic final field this$0: CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1
     inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2
-    inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2$1
     public method <init>(p0: Sink, p1: CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1): void
     public method close(@org.jetbrains.annotations.Nullable p0: java.lang.Throwable): void
     public @org.jetbrains.annotations.Nullable method send(p0: java.lang.Object, @org.jetbrains.annotations.NotNull p1: kotlin.coroutines.Continuation): java.lang.Object
@@ -202,7 +187,6 @@ public final class CrossinlineKt$filter$$inlined$source$1$1 {
 }
 
 @kotlin.Metadata
-@kotlin.coroutines.jvm.internal.DebugMetadata
 public final class CrossinlineKt$filter$$inlined$source$1$lambda$1$1 {
     enclosing method CrossinlineKt$filter$$inlined$source$1$lambda$1.send(Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
     field label: int

compiler/testData/codegen/box/coroutines/tailCallOptimizations/crossinline_ir.txt

@@ -12,26 +12,12 @@ public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$1 {
     public final @org.jetbrains.annotations.Nullable method invokeSuspend(@org.jetbrains.annotations.NotNull p0: java.lang.Object): java.lang.Object
 }
 
-@kotlin.Metadata
-@kotlin.coroutines.jvm.internal.DebugMetadata
-public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2$1 {
-    enclosing method CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2.send(Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
-    field label: int
-    synthetic field result: java.lang.Object
-    synthetic final field this$0: CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2
-    inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2
-    inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2$1
-    public method <init>(p0: CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2, p1: kotlin.coroutines.Continuation): void
-    public final @org.jetbrains.annotations.Nullable method invokeSuspend(@org.jetbrains.annotations.NotNull p0: java.lang.Object): java.lang.Object
-}
-
 @kotlin.Metadata
 public final class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2 {
     // source: 'crossinline.kt'
     enclosing method CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1.consume(LSink;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
     synthetic final field $this_source$inlined: Sink
     inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2
-    inner (anonymous) class CrossinlineKt$box$1$invokeSuspend$$inlined$filter$1$2$1
     public method <init>(p0: Sink): void
     public method close(@org.jetbrains.annotations.Nullable p0: java.lang.Throwable): void
     public @org.jetbrains.annotations.Nullable method send(p0: java.lang.Object, @org.jetbrains.annotations.NotNull p1: kotlin.coroutines.Continuation): java.lang.Object
@@ -130,7 +116,6 @@ public final class CrossinlineKt$filter$$inlined$source$1 {
 }
 
 @kotlin.Metadata
-@kotlin.coroutines.jvm.internal.DebugMetadata
 public final class CrossinlineKt$filter$lambda-3$$inlined$consumeEach$1$1 {
     enclosing method CrossinlineKt$filter$lambda-3$$inlined$consumeEach$1.send(Ljava/lang/Object;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
     field label: int

compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/inline.kt

@@ -0,0 +1,38 @@
+// TARGET_BACKEND: JVM
+// FULL_JDK
+// WITH_RUNTIME
+// WITH_COROUTINES
+// CHECK_TAIL_CALL_OPTIMIZATION
+import helpers.*
+import kotlin.coroutines.*
+import kotlin.coroutines.intrinsics.*
+
+private var x = 100
+
+private inline fun inlineFun(
+    potentiallySuspendLambda: () -> Unit
+) {
+    if (x == 99) return
+    potentiallySuspendLambda()
+}
+
+suspend fun myFunWithTailCall() = inlineFun(
+    potentiallySuspendLambda = { suspendFun() }
+)
+
+suspend fun suspendFun(): Unit = suspendCoroutineUninterceptedOrReturn { x ->
+    TailCallOptimizationChecker.saveStackTrace(x)
+    COROUTINE_SUSPENDED
+}
+
+fun builder(c: suspend () -> Unit) {
+    c.startCoroutine(EmptyContinuation)
+}
+
+fun box(): String {
+    builder {
+        myFunWithTailCall()
+    }
+    TailCallOptimizationChecker.checkNoStateMachineIn("myFunWithTailCall")
+    return "OK"
+}

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

@@ -12042,6 +12042,12 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                     runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/functionReference.kt");
                 }
 
+                @Test
+                @TestMetadata("inline.kt")
+                public void testInline() throws Exception {
+                    runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/inline.kt");
+                }
+
                 @Test
                 @TestMetadata("override.kt")
                 public void testOverride() throws Exception {

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

@@ -12144,6 +12144,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                     runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/functionReference.kt");
                 }
 
+                @Test
+                @TestMetadata("inline.kt")
+                public void testInline() throws Exception {
+                    runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/inline.kt");
+                }
+
                 @Test
                 @TestMetadata("override.kt")
                 public void testOverride() throws Exception {

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

@@ -9683,6 +9683,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                     runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/functionReference.kt");
                 }
 
+                @TestMetadata("inline.kt")
+                public void testInline() throws Exception {
+                    runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/inline.kt");
+                }
+
                 @TestMetadata("override.kt")
                 public void testOverride() throws Exception {
                     runTest("compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/override.kt");