JVM_IR: Generate private suspend functions as synthetic package-private

Do not generate accessors for them.
 #KT-37086 Fixed

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

@@ -173,7 +173,9 @@ open class FunctionCodegen(
         }
         val nativeFlag = if (irFunction.isExternal) Opcodes.ACC_NATIVE else 0
         val syntheticFlag =
-            if (irFunction.origin.isSynthetic || irFunction.hasAnnotation(JVM_SYNTHETIC_ANNOTATION_FQ_NAME)) Opcodes.ACC_SYNTHETIC
+            if (irFunction.origin.isSynthetic || irFunction.hasAnnotation(JVM_SYNTHETIC_ANNOTATION_FQ_NAME) ||
+                    (irFunction.isSuspend && irFunction.visibility == Visibilities.PRIVATE && !irFunction.isInline)
+            ) Opcodes.ACC_SYNTHETIC
             else 0
         val strictFpFlag = if (irFunction.hasAnnotation(STRICTFP_ANNOTATION_FQ_NAME)) Opcodes.ACC_STRICT else 0
         val synchronizedFlag = if (irFunction.hasAnnotation(SYNCHRONIZED_ANNOTATION_FQ_NAME)) Opcodes.ACC_SYNCHRONIZED else 0

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/SyntheticAccessorLowering.kt

@@ -576,6 +576,8 @@ internal class SyntheticAccessorLowering(val context: JvmBackendContext) : IrEle
                 ((thisObjReference == null || contextDeclarationContainer.symbol.isSubtypeOfClass(thisObjReference)) &&
                         (contextDeclarationContainer.isSubclassOf(symbolDeclarationContainer)))
         return when {
+            // private suspend functions are generated as synthetic package private
+            declaration is IrFunction && declaration.isSuspend && declaration.visibility.isPrivate && samePackage -> true
             declaration.visibility.isPrivate && symbolDeclarationContainer != contextDeclarationContainer -> false
             declaration.visibility.isProtected && !samePackage && !fromSubclassOfReceiversClass -> false
             withSuper && !fromSubclassOfReceiversClass -> false

compiler/testData/codegen/bytecodeListing/coroutines/privateAccessor.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-// TODO: KT-37086
 // WITH_RUNTIME
 // COMMON_COROUTINES_TEST
 import COROUTINES_PACKAGE.*

compiler/testData/codegen/bytecodeListing/coroutines/privateAccessor_ir.txt

@@ -0,0 +1,6 @@
+@kotlin.Metadata
+public final class PrivateAccessorKt {
+    public synthetic final static method access$foo(): void
+    synthetic final static method bar(p0: kotlin.coroutines.Continuation): java.lang.Object
+    private final static method foo(): void
+}