SI-8988 Escaping character in StringLike.split(c) prevents usage of optimized String.split code path

Escaping a char when calling split is slow.  We end up compiling a
Pattern to simply match a character literal.

Instead, we just use an loop with indexOf to construct our resulting
Array.

Current speed up over old behaviour is about 12-1

1 files changed, 28 insertions, 3 deletions

diff --git a/src/library/scala/collection/immutable/StringLike.scala b/src/library/scala/collection/immutable/StringLike.scala
index f0daaf25a5..1ead894faf 100644
--- a/src/library/scala/collection/immutable/StringLike.scala
+++ b/src/library/scala/collection/immutable/StringLike.scala
@@ -10,7 +10,7 @@ package scala
 package collection
 package immutable
 
-import mutable.Builder
+import mutable.{ ArrayBuilder, Builder }
 import scala.util.matching.Regex
 import scala.math.ScalaNumber
 import scala.reflect.ClassTag
@@ -203,8 +203,33 @@ self =>
 
   private def escape(ch: Char): String = "\\Q" + ch + "\\E"
 
-  @throws(classOf[java.util.regex.PatternSyntaxException])
-  def split(separator: Char): Array[String] = toString.split(escape(separator))
+  def split(separator: Char): Array[String] = {
+    val thisString = toString
+    var pos = thisString.indexOf(separator)
+
+    if (pos != -1) {
+      val res = new ArrayBuilder.ofRef[String]
+
+      var prev = 0
+      do {
+        res += thisString.substring(prev, pos)
+        prev = pos + 1
+        pos = thisString.indexOf(separator, prev)
+      } while (pos != -1)
+
+      if (prev != thisString.size)
+        res += thisString.substring(prev, thisString.size)
+
+      val initialResult = res.result()
+      pos = initialResult.length
+      while (pos > 0 && initialResult(pos - 1).isEmpty) pos = pos - 1
+      if (pos != initialResult.length) {
+        val trimmed = new Array[String](pos)
+        Array.copy(initialResult, 0, trimmed, 0, pos)
+        trimmed
+      } else initialResult
+    } else Array[String](thisString)
+  }
 
   @throws(classOf[java.util.regex.PatternSyntaxException])
   def split(separators: Array[Char]): Array[String] = {