From 8f0577c603ac86e9bb1cc8fc01bb74f01501b5dc Mon Sep 17 00:00:00 2001
From: Lukas Rytz <lukas.rytz@gmail.com>
Date: Thu, 9 Dec 2021 19:20:16 +0100
Subject: [PATCH] Don't emit `releaseFence` for class params of specialized
 classes

Non-specialized val fields in a specialized class are made non-final
because of the way specialization is encoded. A `releaseFence` call
is added to the constructor to ensure safe publication.

The releaseFence call is not necessary for class parameters as those
remain final.

Follow-up for #9704, fixes scala/bug#12500
---
 src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala | 2 +-
 test/junit/scala/tools/nsc/backend/jvm/BytecodeTest.scala    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala b/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala
index 20f3b8c59486..14077bb69e49 100644
--- a/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala
+++ b/src/compiler/scala/tools/nsc/transform/SpecializeTypes.scala
@@ -750,7 +750,7 @@ abstract class SpecializeTypes extends InfoTransform with TypingTransformers {
 
       for (m <- normMembers) {
         if (!needsSpecialization(fullEnv, m)) {
-          if (m.isValue && !m.isMutable && !m.isMethod && !m.isDeferred && !m.isLazy) {
+          if (m.isValue && !m.isMutable && !m.isMethod && !m.isDeferred && !m.isLazy && !m.isParamAccessor) {
             // non-specialized `val` fields are made mutable (in Constructors) and assigned from the
             // constructors of specialized subclasses. See PR scala/scala#9704.
             clazz.primaryConstructor.updateAttachment(ConstructorNeedsFence)
diff --git a/test/junit/scala/tools/nsc/backend/jvm/BytecodeTest.scala b/test/junit/scala/tools/nsc/backend/jvm/BytecodeTest.scala
index f7a0de1c5372..44983abe6524 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/BytecodeTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/BytecodeTest.scala
@@ -393,7 +393,7 @@ class BytecodeTest extends BytecodeTesting {
   @Test
   def nonSpecializedValFence(): Unit = {
     def code(u1: String) =
-      s"""abstract class Speck[@specialized(Int) T](t: T) {
+      s"""abstract class Speck[@specialized(Int) T](t: T, sm: String, val sn: String) {
          |  val a = t
          |  $u1
          |  lazy val u2 = "?"