SI-2818 Make List.foldRight always do a reverse/foldLeft flip

Benchmarks show that lists smaller than 110 elements or so doing
reverse/foldLeft is faster than recursively walking to the end of
the list and then folding as the stack unwinds.

Above that 110 element threshold the recursive procedure is faster.
Unfortunately, at some magic unknown large size the recursive procedure
blows the stack.

This commit changes List#foldRight to always do reverse/foldLeft.

1 files changed, 6 insertions, 0 deletions

diff --git a/test/files/run/t2818.scala b/test/files/run/t2818.scala
new file mode 100644
index 0000000000..19b67cbc88
--- /dev/null
+++ b/test/files/run/t2818.scala
@@ -0,0 +1,6 @@
+object Test extends App {
+  println((List.range(1L, 15L) :\ 0L) (_ + _))
+  println((List.range(1L, 1000000L) :\ 0L) (_ + _))
+  println((List.fill(5)(1) :\ 1) (_ - _)) 
+  println((List.fill(1000000)(1) :\ 1) (_ - _)) 
+}