Merge pull request #6183 from rorygraves/mike/2.12_x-Backend-CHM

use java concurrent hash map for speed in GenBCode

Author: retronym

src/compiler/scala/tools/nsc/backend/jvm/BTypes.scala

@@ -6,7 +6,6 @@
 package scala.tools.nsc
 package backend.jvm
 
-import scala.collection.concurrent.TrieMap
 import scala.collection.{concurrent, mutable}
 import scala.tools.asm
 import scala.tools.asm.Opcodes
@@ -41,8 +40,8 @@ abstract class BTypes {
 
   // Concurrent maps because stack map frames are computed when in the class writer, which
   // might run on multiple classes concurrently.
-  val classBTypeCacheFromSymbol: concurrent.Map[InternalName, ClassBType] = recordPerRunCache(TrieMap.empty)
-  val classBTypeCacheFromClassfile: concurrent.Map[InternalName, ClassBType] = recordPerRunCache(TrieMap.empty)
+  val classBTypeCacheFromSymbol: concurrent.Map[InternalName, ClassBType] = recordPerRunCache(FlatConcurrentHashMap.empty)
+  val classBTypeCacheFromClassfile: concurrent.Map[InternalName, ClassBType] = recordPerRunCache(FlatConcurrentHashMap.empty)
 
   /**
    * A BType is either a primitive type, a ClassBType, an ArrayBType of one of these, or a MethodType
@@ -1030,3 +1029,8 @@ object BTypes {
   // when inlining, local variable names of the callee are prefixed with the name of the callee method
   val InlinedLocalVariablePrefixMaxLenght = 128
 }
+object FlatConcurrentHashMap {
+  import collection.JavaConverters._
+  def empty[K,V]: concurrent.Map[K,V] =
+    new java.util.concurrent.ConcurrentHashMap[K,V].asScala
+}