Warn when combining settings for the old optimizer with -YGenBCode

Remove some unnecessary flags files
 - neg/t4425.flags
 - run/blame_eye_triple_eee-double.flags
 - run/blame_eye_triple_eee-float.flags

Force tests that use -optimize to GenASM
 - neg/sealed-final-neg.flags
 - pos/inline-access-levels.flags
 - pos/inliner2.flags
 - pos/sealed-final.flags
 - pos/t3420.flags
 - pos/t8410.flags
 - run/constant-optimization.flags
 - run/dead-code-elimination.flags
 - run/elidable-opt.flags
 - run/finalvar.flags
 - run/icode-reader-dead-code.scala
 - run/optimizer-array-load.flags
 - run/synchronized.flags
 - run/t3509.flags
 - run/t3569.flags
 - run/t4285.flags
 - run/t4935.flags
 - run/t5789.scala
 - run/t6188.flags
 - run/t7459b-optimize.flags
 - run/t7582.flags
 - run/t7582b.flags
 - run/t8601.flags
 - run/t8601b.flags
 - run/t8601c.flags
 - run/t8601d.flags
 - run/t8601e.flags
 - run/t9003.flags

Move some tests to the new optimizer
 - run/classfile-format-51.scala
 - run/classfile-format-52.scala
 - run/run-bug4840.flags
 - run/t2106.flags
 - run/t6102.flags

1 files changed, 17 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
index eb4c1aee83..dedf268b56 100644
--- a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
+++ b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
@@ -388,6 +388,23 @@ trait ScalaSettings extends AbsScalaSettings
     val Normal = "normal"
     val Discard = "discard"
   }
+
+  def conflictWarning: Option[String] = {
+    def oldOptimiseFlagsInGenBCode: Option[String] = {
+      val optFlags: List[Setting] = if (optimise.value) List(optimise) else optimiseSettings.filter(_.value)
+      if (isBCodeActive && optFlags.nonEmpty) {
+        val msg = s"""Compiler settings for the 2.11 optimizer (${optFlags.map(_.name).mkString(", ")}) are incompatible with -Ybackend:GenBCode (which is the default in 2.12).
+                     |The optimizer settings are ignored. See -Yopt:help for enabling the new optimizer in 2.12.""".stripMargin
+        Some(msg)
+      } else
+        None
+    }
+
+    List(oldOptimiseFlagsInGenBCode /*, moreToCome */).flatten match {
+      case Nil => None
+      case warnings => Some("Conflicting compiler settings were detected. Some settings will be ignored.\n" + warnings.mkString("\n"))
+    }
+  }
 }
 
 object ClassPathRepresentationType {