[vpm] unapplyProd: faster matching for case classes

behold the mythical unapplyProd: it does not exist, yet it promises to speed up pattern matching on case classes

instead of calling the synthetic unapply/unapplySeq, we don't call the mythical synthetic unapplyProd,
since -- if it existed -- it would be the identity anyway for case classes

eventually, we will allow user-defined unapplyProd's, which should give you almost the same speed as case class matching
for user-defined extractors (i.e., you don't have to wrap in an option, just return something on which we can select _i for i = 1 to N, unless it is null, which indicates match failure)

still need to figure out a way to derive the types for the subpatterns, without requiring you to wrap your result in a ProductN

unapplyProd support for vararg case classes

using caseFieldAccessors instead of synthetic _i

now the compiler bootstraps again, and after this optimization, quick.lib overhead is 70%, quick.comp is 50%
(compiling with a locker built using -Yvirtpatmat, and itself generating code for -Yvirtpatmat)
before the optimization, I think the overhead for quick.comp was close to 100% in this scenario

more robust tupleSel for case classes

TODO:
  - pos/t602 -- clean up after type inference as in fromCaseClassUnapply
  - run/pf-catch -- implement new-style orElse for partial function in uncurry

3 files changed, 28 insertions, 0 deletions

diff --git a/test/files/run/virtpatmat_unapplyprod.check b/test/files/run/virtpatmat_unapplyprod.check
new file mode 100644
index 0000000000..2660ff8f96
--- /dev/null
+++ b/test/files/run/virtpatmat_unapplyprod.check
@@ -0,0 +1,4 @@
+(2,3)
+(2,3)
+(2,3)
+List(true, false, true)
diff --git a/test/files/run/virtpatmat_unapplyprod.flags b/test/files/run/virtpatmat_unapplyprod.flags
new file mode 100644
index 0000000000..9769db9257
--- /dev/null
+++ b/test/files/run/virtpatmat_unapplyprod.flags
@@ -0,0 +1 @@
+ -Yvirtpatmat -Xexperimental
diff --git a/test/files/run/virtpatmat_unapplyprod.scala b/test/files/run/virtpatmat_unapplyprod.scala
new file mode 100644
index 0000000000..441e5e3968
--- /dev/null
+++ b/test/files/run/virtpatmat_unapplyprod.scala
@@ -0,0 +1,23 @@
+object Test extends App {
+  case class Foo(x: Int, y: String)
+
+  Foo(2, "3") match {
+    case Foo(x, y) => println((x, y))
+  }
+
+  case class FooSeq(x: Int, y: String, z: Boolean*)
+
+  FooSeq(2, "3") match {
+    case FooSeq(x, y) => println((x, y))
+  }
+
+  FooSeq(2, "3", true, false, true) match {
+    case FooSeq(x, y) => println("nope")
+    case FooSeq(x, y, true, false, true) => println((x, y))
+  }
+
+  FooSeq(1, "a", true, false, true) match {
+    case FooSeq(1, "a") => println("nope")
+    case FooSeq(1, "a", x@_* ) => println(x.toList)
+  }
+}
\ No newline at end of file