Minor, add comment to synthetic accessor generation for super calls

Also fix "useless elvis" warning in SyntheticAccessorLowering.

compiler/backend/src/org/jetbrains/kotlin/codegen/syntheticAccessorUtil.kt

@@ -33,7 +33,8 @@ private fun CallableMemberDescriptor.getJvmName() =
 fun getAccessorNameSuffix(
     descriptor: CallableMemberDescriptor, superCallDescriptor: ClassDescriptor?, accessorKind: AccessorKind
 ): String {
-    if (accessorKind == AccessorKind.JVM_DEFAULT_COMPATIBILITY) return descriptor.getJvmName() + "$" + AccessorKind.JVM_DEFAULT_COMPATIBILITY.suffix
+    if (accessorKind == AccessorKind.JVM_DEFAULT_COMPATIBILITY)
+        return descriptor.getJvmName() + "$" + AccessorKind.JVM_DEFAULT_COMPATIBILITY.suffix
 
     val suffix = when (descriptor) {
         is ConstructorDescriptor ->
@@ -45,5 +46,9 @@ fun getAccessorNameSuffix(
         else ->
             throw UnsupportedOperationException("Do not know how to create accessor for descriptor $descriptor")
     }
-    return if (superCallDescriptor == null) suffix else "$suffix\$s${superCallDescriptor.name.asString().hashCode()}"
+    return if (superCallDescriptor == null) suffix else "$suffix\$s${superCallDescriptor.syntheticAccessorToSuperSuffix()}"
 }
+
+fun ClassDescriptor.syntheticAccessorToSuperSuffix(): String =
+    // TODO: change this to `fqNameUnsafe.asString().replace(".", "_")` as soon as we're ready to break compatibility with pre-KT-21178 code
+    name.asString().hashCode().toString()

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

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.backend.jvm.ir.IrInlineReferenceLocator
 import org.jetbrains.kotlin.backend.jvm.ir.hasJvmDefault
 import org.jetbrains.kotlin.backend.jvm.ir.isLambda
 import org.jetbrains.kotlin.backend.jvm.lower.inlineclasses.hasMangledParameters
+import org.jetbrains.kotlin.codegen.syntheticAccessorToSuperSuffix
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.Visibility
@@ -467,11 +468,11 @@ internal class SyntheticAccessorLowering(val context: JvmBackendContext) : IrEle
             parentAsClass.isJvmInterface -> if (!Visibilities.isPrivate(visibility) && hasJvmDefault()) "\$jd" else ""
 
             // Accessor for _s_uper-qualified call
-            superQualifier != null -> "\$s" + superQualifier.descriptor.name.asString().hashCode()
+            superQualifier != null -> "\$s" + superQualifier.descriptor.syntheticAccessorToSuperSuffix()
 
             // Access to static members that need an accessor must be because they are inherited,
             // hence accessed on a _s_upertype.
-            isStatic -> "\$s" + hashForAccessorDisambiguation()
+            isStatic -> "\$s" + parentAsClass.descriptor.syntheticAccessorToSuperSuffix()
 
             else -> ""
         }
@@ -496,17 +497,10 @@ internal class SyntheticAccessorLowering(val context: JvmBackendContext) : IrEle
 
         // Static accesses that need an accessor must be due to being inherited, hence accessed on a
         // _s_upertype
-        val staticSuffix = if (isStatic) "\$s"+ hashForAccessorDisambiguation() else ""
+        val staticSuffix = if (isStatic) "\$s" + parentAsClass.descriptor.syntheticAccessorToSuperSuffix() else ""
         return companionSuffix + staticSuffix
     }
 
-    private fun IrDeclaration.hashForAccessorDisambiguation() =
-        if (parentAsClass.name.isSpecial) {
-            context.getLocalClassType(parentAsClass)?.className.hashCode() ?: parentAsClass.name.hashCode()
-        } else {
-            parentAsClass.name.identifier.hashCode()
-        }
-
     private val Visibility.isPrivate
         get() = Visibilities.isPrivate(this)