IR: make calls with explicit singleton receiver tailrec [KT-48602]

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirTailrecFunctionChecker.kt

@@ -20,7 +20,9 @@ import org.jetbrains.kotlin.fir.expressions.impl.FirNoReceiverExpression
 import org.jetbrains.kotlin.fir.expressions.toResolvedCallableSymbol
 import org.jetbrains.kotlin.fir.resolve.dfa.cfg.*
 import org.jetbrains.kotlin.fir.resolve.dfa.controlFlowGraph
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
+import org.jetbrains.kotlin.fir.types.toSymbol
 
 object FirTailrecFunctionChecker : FirSimpleFunctionChecker() {
     override fun check(declaration: FirSimpleFunction, context: CheckerContext, reporter: DiagnosticReporter) {
@@ -80,8 +82,8 @@ object FirTailrecFunctionChecker : FirSimpleFunctionChecker() {
                 }
                 val dispatchReceiver = functionCall.dispatchReceiver
                 // A tailrec call does not support changing dispatchers. Here we report changing dispatch receiver if the dispatch receiver
-                // is present and not a `this`. For the `this` check, we don't need to actually compare if the dispatch receiver `this`
+                // is present and not a `this` or a singleton. For the `this` check, we don't need to actually compare if the dispatch
-                // references the same `this` made available from `declaration`. This is because
+                // receiver `this` references the same `this` made available from `declaration`. This is because
                 // 1. if `this` is not labeled, then it references the innermost `this` receiver. If the innermost scope is not the
                 //    `declaration` body, then follow-up checks on following nodes would report there to be more instructions, which would
                 //    then make this call non-tailrec.
@@ -93,9 +95,10 @@ object FirTailrecFunctionChecker : FirSimpleFunctionChecker() {
                 //       is already bailed out earlier. So there is no need to report anything.
                 //    c. `declaration` is a member function of an inner class and the receiver is a labeled `this` pointing to the outer
                 //       class. The reasoning is the same with b.
-                // Also note that if the dispatch receiver is explicitly specify to be a singleton, the call is not compiled as a tailrec
+                if (dispatchReceiver !is FirThisReceiverExpression &&
-                // either. See KT-48602.
+                    dispatchReceiver !is FirNoReceiverExpression &&
-                if (dispatchReceiver !is FirThisReceiverExpression && dispatchReceiver !is FirNoReceiverExpression) {
+                    (declaration.dispatchReceiverType?.toSymbol(context.session) as? FirClassSymbol<*>)?.classKind?.isSingleton != true
+                ) {
                     reporter.reportOn(functionCall.source, FirErrors.NON_TAIL_RECURSIVE_CALL, context)
                     return
                 }

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

@@ -14584,6 +14584,18 @@ public class FirBlackBoxCodegenTestGenerated extends AbstractFirBlackBoxCodegenT
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailRecursionInFinally.kt");
                 }
 
+                @Test
+                @TestMetadata("tailrecWithExplicitCompanionObjectDispatcher.kt")
+                public void testTailrecWithExplicitCompanionObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt");
+                }
+
+                @Test
+                @TestMetadata("tailrecWithExplicitObjectDispatcher.kt")
+                public void testTailrecWithExplicitObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt");
+                }
+
                 @Test
                 @TestMetadata("thisReferences.kt")
                 public void testThisReferences() throws Exception {

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/TailRecursionCallsCollector.kt

@@ -16,11 +16,14 @@
 
 package org.jetbrains.kotlin.backend.common
 
+import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
 import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.types.IrSimpleType
+import org.jetbrains.kotlin.ir.types.classOrNull
 import org.jetbrains.kotlin.ir.types.isUnit
 import org.jetbrains.kotlin.ir.util.usesDefaultArguments
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
@@ -107,6 +110,13 @@ fun collectTailRecursionCalls(irFunction: IrFunction): Set<IrCall> {
                 // Overridden functions using default arguments at tail call are not included: KT-4285
                 return
             }
+            val dispatchReceiverType = irFunction.dispatchReceiverParameter?.type
+            if (dispatchReceiverType?.classOrNull?.owner?.kind?.isSingleton == true) {
+                // Dispatch receiver type is singleton and hence it can't be changed and the call must be tailrec.
+                result.add(expression)
+                return
+            }
+
 
             expression.dispatchReceiver?.let {
                 if (it !is IrGetValue || it.symbol.owner != irFunction.dispatchReceiverParameter) {

compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt

@@ -0,0 +1,25 @@
+// DONT_TARGET_EXACT_BACKEND: WASM
+// WASM_MUTE_REASON: IGNORED_IN_JS
+// IGNORE_BACKEND: JS_IR
+// IGNORE_BACKEND: JS_IR_ES6
+// DONT_RUN_GENERATED_CODE: JS
+// IGNORE_BACKEND: JS
+// IGNORE_BACKEND: JVM
+// IGNORE_FIR_DIAGNOSTICS_DIFF
+
+// Light analysis thinks this test passes but it doesn't because JVM backend does not compile this into a tailrec function.
+// IGNORE_LIGHT_ANALYSIS
+
+class C {
+    companion object {
+        <!NO_TAIL_CALLS_FOUND!>tailrec fun rec(i: Int)<!> {
+            if (i <= 0) return
+            C.<!NON_TAIL_RECURSIVE_CALL!>rec<!>(i - 1)
+        }
+    }
+}
+
+fun box(): String {
+    C.rec(100000)
+    return "OK"
+}

compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt

@@ -0,0 +1,16 @@
+// DONT_TARGET_EXACT_BACKEND: WASM
+// WASM_MUTE_REASON: IGNORED_IN_JS
+// IGNORE_BACKEND: JS_IR_ES6
+// DONT_RUN_GENERATED_CODE: JS
+
+object O {
+    tailrec fun rec(i: Int) {
+        if (i <= 0) return
+        O.rec(i - 1)
+    }
+}
+
+fun box(): String {
+    O.rec(100000)
+    return "OK"
+}

compiler/testData/diagnostics/tests/tailRecSingleton.fir.kt

@@ -7,8 +7,8 @@ object Foo {
         this.foo2()
     }
 
-    <!NO_TAIL_CALLS_FOUND!>tailrec fun foo3()<!> {
+    tailrec fun foo3() {
-        Foo.<!NON_TAIL_RECURSIVE_CALL!>foo3<!>()
+        Foo.foo3()
     }
 }
 
@@ -22,12 +22,12 @@ class Bar {
             this.bar2()
         }
 
-        <!NO_TAIL_CALLS_FOUND!>tailrec fun bar3()<!> {
+        tailrec fun bar3() {
-            Bar.<!NON_TAIL_RECURSIVE_CALL!>bar3<!>()
+            Bar.bar3()
         }
 
-        <!NO_TAIL_CALLS_FOUND!>tailrec fun bar4()<!> {
+        tailrec fun bar4() {
-            Bar.Companion.<!NON_TAIL_RECURSIVE_CALL!>bar4<!>()
+            Bar.Companion.bar4()
         }
     }
 }

compiler/testData/diagnostics/tests/tailRecursionComplex.fir.kt

@@ -1,16 +0,0 @@
-object O {
-    // foo is the same, but the compiler currently doesn't compile this as tail recursive. See KT-48602
-    <!NO_TAIL_CALLS_FOUND!>tailrec fun foo(i: Int): Int<!> = if (i < 0) 0 else O.<!NON_TAIL_RECURSIVE_CALL!>foo<!>(i - 1)
-}
-
-class A {
-    <!NO_TAIL_CALLS_FOUND!>tailrec fun foo(i: Int)<!> = if (i < 0) 0 else A.foo(i - 1)
-
-    companion object {
-        fun foo(i: Int) = 42 + i
-    }
-}
-
-class B {
-    <!NO_TAIL_CALLS_FOUND!>tailrec fun foo(i: Int)<!> = if (i < 0) 0 else O.foo(i - 1)
-}

compiler/testData/diagnostics/tests/tailRecursionComplex.kt

@@ -1,5 +1,6 @@
+// FIR_IDENTICAL
 object O {
-    // foo is the same, but the compiler currently doesn't compile this as tail recursive. See KT-48602
+    // tailrec since `O` is a singleton
     tailrec fun foo(i: Int): Int = if (i < 0) 0 else O.foo(i - 1)
 }
 

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

@@ -14506,6 +14506,18 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailRecursionInFinally.kt");
                 }
 
+                @Test
+                @TestMetadata("tailrecWithExplicitCompanionObjectDispatcher.kt")
+                public void testTailrecWithExplicitCompanionObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt");
+                }
+
+                @Test
+                @TestMetadata("tailrecWithExplicitObjectDispatcher.kt")
+                public void testTailrecWithExplicitObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt");
+                }
+
                 @Test
                 @TestMetadata("thisReferences.kt")
                 public void testThisReferences() throws Exception {

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

@@ -14584,6 +14584,18 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailRecursionInFinally.kt");
                 }
 
+                @Test
+                @TestMetadata("tailrecWithExplicitCompanionObjectDispatcher.kt")
+                public void testTailrecWithExplicitCompanionObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt");
+                }
+
+                @Test
+                @TestMetadata("tailrecWithExplicitObjectDispatcher.kt")
+                public void testTailrecWithExplicitObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt");
+                }
+
                 @Test
                 @TestMetadata("thisReferences.kt")
                 public void testThisReferences() throws Exception {

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

@@ -11684,6 +11684,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/recursiveCallInInlineLambdaWithCapture.kt");
                 }
 
+                @TestMetadata("tailrecWithExplicitCompanionObjectDispatcher.kt")
+                public void ignoreTailrecWithExplicitCompanionObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt");
+                }
+
                 private void runTest(String testDataFilePath) throws Exception {
                     KotlinTestUtils.runTest(this::doTest, TargetBackend.JVM, testDataFilePath);
                 }
@@ -11867,6 +11872,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailRecursionInFinally.kt");
                 }
 
+                @TestMetadata("tailrecWithExplicitObjectDispatcher.kt")
+                public void testTailrecWithExplicitObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt");
+                }
+
                 @TestMetadata("thisReferences.kt")
                 public void testThisReferences() throws Exception {
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/thisReferences.kt");

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/es6/semantics/IrJsCodegenBoxES6TestGenerated.java

@@ -10586,6 +10586,16 @@ public class IrJsCodegenBoxES6TestGenerated extends AbstractIrJsCodegenBoxES6Tes
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailRecursionInFinally.kt");
                 }
 
+                @TestMetadata("tailrecWithExplicitCompanionObjectDispatcher.kt")
+                public void testTailrecWithExplicitCompanionObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt");
+                }
+
+                @TestMetadata("tailrecWithExplicitObjectDispatcher.kt")
+                public void testTailrecWithExplicitObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt");
+                }
+
                 @TestMetadata("thisReferences.kt")
                 public void testThisReferences() throws Exception {
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/thisReferences.kt");

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/ir/semantics/IrJsCodegenBoxTestGenerated.java

@@ -9992,6 +9992,16 @@ public class IrJsCodegenBoxTestGenerated extends AbstractIrJsCodegenBoxTest {
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailRecursionInFinally.kt");
                 }
 
+                @TestMetadata("tailrecWithExplicitCompanionObjectDispatcher.kt")
+                public void testTailrecWithExplicitCompanionObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt");
+                }
+
+                @TestMetadata("tailrecWithExplicitObjectDispatcher.kt")
+                public void testTailrecWithExplicitObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt");
+                }
+
                 @TestMetadata("thisReferences.kt")
                 public void testThisReferences() throws Exception {
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/thisReferences.kt");

js/js.tests/tests-gen/org/jetbrains/kotlin/js/test/semantics/JsCodegenBoxTestGenerated.java

@@ -9972,6 +9972,16 @@ public class JsCodegenBoxTestGenerated extends AbstractJsCodegenBoxTest {
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailRecursionInFinally.kt");
                 }
 
+                @TestMetadata("tailrecWithExplicitCompanionObjectDispatcher.kt")
+                public void testTailrecWithExplicitCompanionObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitCompanionObjectDispatcher.kt");
+                }
+
+                @TestMetadata("tailrecWithExplicitObjectDispatcher.kt")
+                public void testTailrecWithExplicitObjectDispatcher() throws Exception {
+                    runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/tailrecWithExplicitObjectDispatcher.kt");
+                }
+
                 @TestMetadata("thisReferences.kt")
                 public void testThisReferences() throws Exception {
                     runTest("compiler/testData/codegen/box/diagnostics/functions/tailRecursion/thisReferences.kt");