First version of inliningh heuristics that prefer higher-order methos

When invoking a higher-order method and the value passed for the
SAM type is either a function literal or a parameter of the callsite
method, inline the higher-order method into the callee.

This is a first version, the heuristics will be refined further.

2 files changed, 12 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala
index cd10094204..e559b63c09 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/InlinerHeuristics.scala
@@ -84,8 +84,16 @@ class InlinerHeuristics[BT <: BTypes](val bTypes: BT) {
       if (callee.safeToInline && callee.annotatedInline) Some(InlineRequest(callsite, Nil))
       else None
 
-//    case "default" =>
-
+    case "default" =>
+      val callee = callsite.callee.get
+      if (callee.safeToInline && !callee.annotatedNoInline) {
+        val shouldInlineHO = callee.samParamTypes.nonEmpty && (callee.samParamTypes exists {
+          case (index, _) => callsite.argInfos.contains(index)
+        })
+
+        if (shouldInlineHO || callee.annotatedInline) Some(InlineRequest(callsite, Nil))
+        else None
+      } else None
   }
 
   /*
diff --git a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
index ea9ad1d909..74d152a4cf 100644
--- a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
+++ b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
@@ -276,8 +276,8 @@ trait ScalaSettings extends AbsScalaSettings
     name = "-Yopt-inline-heuristics",
     helpArg = "strategy",
     descr = "Set the heuristics for inlining decisions.",
-    choices = List("at-inline-annotated", "everything"),
-    default = "at-inline-annotated")
+    choices = List("at-inline-annotated", "everything", "default"),
+    default = "default")
 
   object YoptWarningsChoices extends MultiChoiceEnumeration {
     val none                               = Choice("none"                       , "No optimizer warnings.")