Limit unnecessary calls to Type#toString.

Logging revealed a few thousand calls to the often expensive
Type#toString emerging from tailcalls. The error message was
being generated for all methods even though it was only issued
in rare cases (and for the particular tailrec failure which
made the call, extremely rare.)

The remaining boatload of unnecessary Type#toString calls are
much harder to fix due to the design of "AbsTypeError" and the
fact that the compiler approaches mutability like a cat approaches
a loaded gun. See SI-6149.

1 files changed, 6 insertions, 6 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/TailCalls.scala b/src/compiler/scala/tools/nsc/transform/TailCalls.scala
index 9e867917f9..6f422fcc90 100644
--- a/src/compiler/scala/tools/nsc/transform/TailCalls.scala
+++ b/src/compiler/scala/tools/nsc/transform/TailCalls.scala
@@ -89,12 +89,12 @@ abstract class TailCalls extends Transform {
    */
   class TailCallElimination(unit: CompilationUnit) extends Transformer {
     private def defaultReason = "it contains a recursive call not in tail position"
-    private val failPositions = perRunCaches.newMap[TailContext, Position]()
-    private val failReasons   = perRunCaches.newMap[TailContext, String]()
+    private val failPositions = perRunCaches.newMap[TailContext, Position]() withDefault (_.methodPos)
+    private val failReasons   = perRunCaches.newMap[TailContext, String]() withDefaultValue defaultReason
     private def tailrecFailure(ctx: TailContext) {
-      val method           = ctx.method
-      val failReason       = failReasons.getOrElse(ctx, defaultReason)
-      val failPos          = failPositions.getOrElse(ctx, ctx.methodPos)
+      val method      = ctx.method
+      val failReason  = failReasons(ctx)
+      val failPos     = failPositions(ctx)
 
       unit.error(failPos, s"could not optimize @tailrec annotated $method: $failReason")
     }
@@ -237,7 +237,7 @@ abstract class TailCalls extends Transform {
 
         if (!ctx.isEligible)            fail("it is neither private nor final so can be overridden")
         else if (!isRecursiveCall) {
-          if (receiverIsSuper)          failHere("it contains a recursive call targeting supertype " + receiver.tpe)
+          if (receiverIsSuper)          failHere("it contains a recursive call targeting a supertype")
           else                          failHere(defaultReason)
         }
         else if (!matchesTypeArgs)      failHere("it is called recursively with different type arguments")