From c5962b1871f8093fe200fe0c47cd9c202b07a8f9 Mon Sep 17 00:00:00 2001
From: Rex Kerr <ichoran@gmail.com>
Date: Mon, 10 Feb 2014 02:17:27 -0800
Subject: SI-8240 Consider rolling back optimizations for List

Some compiler-specific optimizations turn out to be very helpful for Lists in general.

  * List map can be a lot faster (up to 5x!)
  * List collect can be considerably faster (up to 3x)
  * List flatMap can be a bit faster (2x)
  * List take can be slightly faster (1.1x) and have better structural sharing

These appear to be unqualified wins (tested), even in a scenario with mixed collections.  This is expected: detecting the builder is faster than the otherwise mandatory object creation, and multiple dispatch is mostly a wash since it was already multiple dispatch in getting to the builder.

With -optimize, map is not always such a big win, but is never slower.

Also added @noinline to map to work around an optimizer bug (SI-8334) and added a test to check that the pattern that triggers the optimizer bug does not affect any of the map-like methods.
---
 test/files/pos/list-optim-check.flags |  1 +
 test/files/pos/list-optim-check.scala | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 test/files/pos/list-optim-check.flags
 create mode 100644 test/files/pos/list-optim-check.scala

(limited to 'test/files')

diff --git a/test/files/pos/list-optim-check.flags b/test/files/pos/list-optim-check.flags
new file mode 100644
index 0000000000..49d036a887
--- /dev/null
+++ b/test/files/pos/list-optim-check.flags
@@ -0,0 +1 @@
+-optimize
diff --git a/test/files/pos/list-optim-check.scala b/test/files/pos/list-optim-check.scala
new file mode 100644
index 0000000000..f6e6ddec77
--- /dev/null
+++ b/test/files/pos/list-optim-check.scala
@@ -0,0 +1,21 @@
+// Tests a map known to crash in optimizer with faster List map in SI-8240.
+// Equivalent tests for collect and flatmap do not crash, but are provided
+// anyway.
+// See ticket SI-8334 for optimizer bug.
+// TODO - Remove this test once SI-8334 is fixed and has its own test.
+class A {
+  def f: Boolean = {
+    val xs = Nil map (_ => return false)
+    true
+  }
+
+  def g: Boolean = {
+    val xs = Nil collect { case _ => return false }
+    true
+  }
+
+  def h: Boolean = {
+    val xs = Nil flatMap { _ => return false }
+    true
+  }
+}
-- 
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