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

2 files changed, 21 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
index 965f984367..5cb31c1b64 100644
--- a/src/compiler/scala/tools/nsc/Global.scala
+++ b/src/compiler/scala/tools/nsc/Global.scala
@@ -1373,7 +1373,7 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
       unitbuf += unit
       compiledFiles += unit.source.file.path
     }
-    private def checkDeprecatedSettings(unit: CompilationUnit) {
+    private def warnDeprecatedAndConflictingSettings(unit: CompilationUnit) {
       // issue warnings for any usage of deprecated settings
       settings.userSetSettings filter (_.isDeprecated) foreach { s =>
         currentRun.reporting.deprecationWarning(NoPosition, s.name + " is deprecated: " + s.deprecationMessage.get)
@@ -1383,6 +1383,7 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
         currentRun.reporting.deprecationWarning(NoPosition, settings.target.name + ":" + settings.target.value + " is deprecated and has no effect, setting to " + supportedTarget)
         settings.target.value = supportedTarget
       }
+      settings.conflictWarning.foreach(reporter.warning(NoPosition, _))
     }
 
     /* An iterator returning all the units being compiled in this run */
@@ -1473,7 +1474,7 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
     def compileSources(sources: List[SourceFile]) = if (!reporter.hasErrors) {
 
       def checkDeprecations() = {
-        checkDeprecatedSettings(newCompilationUnit(""))
+        warnDeprecatedAndConflictingSettings(newCompilationUnit(""))
         reporting.summarizeErrors()
       }
 
@@ -1495,7 +1496,7 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
       val startTime = currentTime
 
       reporter.reset()
-      checkDeprecatedSettings(unitbuf.head)
+      warnDeprecatedAndConflictingSettings(unitbuf.head)
       globalPhase = fromPhase
 
       while (globalPhase.hasNext && !reporter.hasErrors) {
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 {