[commit: ghc] master: Add rule mapFB c (λx.x) = c (2fa4421)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/2fa44217c1d9722227297eefb0d6c6aed7e128ca/ghc

>---------------------------------------------------------------

commit 2fa44217c1d9722227297eefb0d6c6aed7e128ca
Author: Joachim Breitner <mail at joachim-breitner.de>
Date:   Mon Mar 6 17:30:52 2017 -0500

    Add rule mapFB c (λx.x) = c
    
    Test Plan: exended T2110 with a case for that.
    
    Reviewers: austin, hvr, dfeuer, bgamari
    
    Reviewed By: dfeuer
    
    Subscribers: dfeuer, thomie
    
    Differential Revision: https://phabricator.haskell.org/D3275


>---------------------------------------------------------------

2fa44217c1d9722227297eefb0d6c6aed7e128ca
 libraries/base/GHC/Base.hs                        | 1 +
 testsuite/tests/simplCore/should_run/T2110.hs     | 3 +++
 testsuite/tests/simplCore/should_run/T2110.stdout | 1 +
 3 files changed, 5 insertions(+)

diff --git a/libraries/base/GHC/Base.hs b/libraries/base/GHC/Base.hs
index 2f155c6..6f9d454 100644
--- a/libraries/base/GHC/Base.hs
+++ b/libraries/base/GHC/Base.hs
@@ -973,6 +973,7 @@ mapFB c f = \x ys -> c (f x) ys
 "map"       [~1] forall f xs.   map f xs                = build (\c n -> foldr (mapFB c f) n xs)
 "mapList"   [1]  forall f.      foldr (mapFB (:) f) []  = map f
 "mapFB"     forall c f g.       mapFB (mapFB c f) g     = mapFB c (f.g)
+"mapFB/id"  forall c.           mapFB c (\x -> x)       = c
   #-}
 
 -- See Breitner, Eisenberg, Peyton Jones, and Weirich, "Safe Zero-cost
diff --git a/testsuite/tests/simplCore/should_run/T2110.hs b/testsuite/tests/simplCore/should_run/T2110.hs
index 610be09..d945fac 100644
--- a/testsuite/tests/simplCore/should_run/T2110.hs
+++ b/testsuite/tests/simplCore/should_run/T2110.hs
@@ -5,6 +5,8 @@ import Unsafe.Coerce
 
 newtype Age = Age Int
 
+foo :: [Int] -> [Int]
+foo = map id
 fooAge :: [Int] -> [Age]
 fooAge = map Age
 fooCoerce :: [Int] -> [Age]
@@ -19,6 +21,7 @@ same x y = case reallyUnsafePtrEquality# (unsafeCoerce x) y of
 
 main = do
     let l = [1,2,3]
+    same (foo l) l
     same (fooAge l) l
     same (fooCoerce l) l
     same (fooUnsafeCoerce l) l
diff --git a/testsuite/tests/simplCore/should_run/T2110.stdout b/testsuite/tests/simplCore/should_run/T2110.stdout
index 55f7ebb..4ff957b 100644
--- a/testsuite/tests/simplCore/should_run/T2110.stdout
+++ b/testsuite/tests/simplCore/should_run/T2110.stdout
@@ -1,3 +1,4 @@
 yes
 yes
 yes
+yes