FIR: special visibility handling for monitor{Enter|Exit}

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/ResolutionStages.kt

@@ -438,7 +438,7 @@ internal object CheckVisibility : CheckerStage() {
                         canSeePrivateMemberOf(containingDeclarations, ownerId, session)
                     }
                 } else {
-                    false
+                    declaration is FirSimpleFunction && declaration.isAllowedToBeAccessedFromOutside()
                 }
             }
             Visibilities.PROTECTED -> {
@@ -461,6 +461,16 @@ internal object CheckVisibility : CheckerStage() {
         return true
     }
 
+    // monitorEnter/monitorExit are the only functions which are accessed "illegally" (see kotlin/util/Synchronized.kt).
+    // Since they are intrinsified in the codegen, FIR should treat it as visible.
+    private fun FirSimpleFunction.isAllowedToBeAccessedFromOutside(): Boolean {
+        if (!isFromLibrary) return false
+        val packageName = symbol.callableId.packageName.asString()
+        val name = name.asString()
+        return packageName == "kotlin.jvm.internal.unsafe" &&
+                (name == "monitorEnter" || name == "monitorExit")
+    }
+
     private fun AbstractFirBasedSymbol<*>.getOwnerId(): ClassId? {
         return when (this) {
             is FirClassLikeSymbol<*> -> {

compiler/testData/codegen/box/intrinsics/monitorEnterMonitorExit.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 
 import kotlin.jvm.internal.unsafe.*