From fe848489b8854fc8a07c2a964483db660d38fbd2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Doeraene?= <sjrdoeraene@gmail.com>
Date: Thu, 19 Nov 2020 17:14:17 +0100
Subject: [PATCH] Make the extension method `nn` inline.

And delegate its body to a runtime method in Scala3RunTime.

With this change, all the methods of DottyPredef are inline
methods. We will therefore be able to patch them on Predef in the
future, rather than having DottyPredef.
---
 .../backend/jvm/InlineBytecodeTests.scala     | 24 +++++++++++++++++++
 library/src/dotty/DottyPredef.scala           |  5 ++--
 library/src/scala/runtime/Scala3RunTime.scala |  8 +++++++
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/compiler/test/dotty/tools/backend/jvm/InlineBytecodeTests.scala b/compiler/test/dotty/tools/backend/jvm/InlineBytecodeTests.scala
index 8fd690aa8633..22350ca5dfef 100644
--- a/compiler/test/dotty/tools/backend/jvm/InlineBytecodeTests.scala
+++ b/compiler/test/dotty/tools/backend/jvm/InlineBytecodeTests.scala
@@ -104,6 +104,30 @@ class InlineBytecodeTests extends DottyBytecodeTest {
     }
   }
 
+  @Test def inlineNn = {
+    val source =
+      s"""
+         |class Foo {
+         |  def meth1(x: Int | Null): Int = x.nn
+         |  def meth2(x: Int | Null): Int = scala.runtime.Scala3RunTime.nn(x)
+         |}
+         """.stripMargin
+
+    checkBCode(source) { dir =>
+      val clsIn = dir.lookupName("Foo.class", directory = false).input
+      val clsNode = loadClassNode(clsIn)
+      val meth1 = getMethod(clsNode, "meth1")
+      val meth2 = getMethod(clsNode, "meth2")
+
+      val instructions1 = instructionsFromMethod(meth1)
+      val instructions2 = instructionsFromMethod(meth2)
+
+      assert(instructions1 == instructions2,
+        "`nn` was not properly inlined in `meth1`\n" +
+        diffInstructions(instructions1, instructions2))
+    }
+  }
+
   @Test def i4947 = {
     val source = """class Foo {
                    |  transparent inline def track[T](inline f: T): T = {
diff --git a/library/src/dotty/DottyPredef.scala b/library/src/dotty/DottyPredef.scala
index 5e2512461386..72412c8c417b 100644
--- a/library/src/dotty/DottyPredef.scala
+++ b/library/src/dotty/DottyPredef.scala
@@ -79,7 +79,6 @@ object DottyPredef {
    *
    *  Note that `.nn` performs a checked cast, so if invoked on a null value it'll throw an NPE.
    */
-  extension [T](x: T | Null) def nn: x.type & T =
-    if (x == null) throw new NullPointerException("tried to cast away nullability, but value is null")
-    else x.asInstanceOf[x.type & T]
+  extension [T](x: T | Null) inline def nn: x.type & T =
+    scala.runtime.Scala3RunTime.nn(x)
 }
diff --git a/library/src/scala/runtime/Scala3RunTime.scala b/library/src/scala/runtime/Scala3RunTime.scala
index 592e4e21396c..fa141628ceec 100644
--- a/library/src/scala/runtime/Scala3RunTime.scala
+++ b/library/src/scala/runtime/Scala3RunTime.scala
@@ -10,4 +10,12 @@ object Scala3RunTime:
   def assertFailed(): Nothing =
     throw new java.lang.AssertionError("assertion failed")
 
+  /** Called by the inline extension def `nn`.
+   *
+   *  Extracted to minimize the bytecode size at call site.
+   */
+  def nn[T](x: T | Null): x.type & T =
+    if (x == null) throw new NullPointerException("tried to cast away nullability, but value is null")
+    else x.asInstanceOf[x.type & T]
+
 end Scala3RunTime