[commit: ghc] wip/validate-T9536: Fusion rule for "foldr k z (x:build g)" (1bc83b8)

[git at git.haskell.org]

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

On branch  : wip/validate-T9536
Link       : http://ghc.haskell.org/trac/ghc/changeset/1bc83b8a3d5ac01357d42b14d513312e98e2bb29/ghc

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

commit 1bc83b8a3d5ac01357d42b14d513312e98e2bb29
Author: David Feuer <David.Feuer at gmail.com>
Date:   Wed Oct 1 15:57:27 2014 +0200

    Fusion rule for "foldr k z (x:build g)"
    
    There seem to be various issues with general fold/cons and even
    cons/build rules, but it seems pretty clear to me that the simple
    fold/cons/build rule is a good idea. It doesn't do much for nofib
    allocation, but it seems to improve some other analyses and speed
    several benchmarks up. Implements #9536.


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

1bc83b8a3d5ac01357d42b14d513312e98e2bb29
 libraries/base/GHC/Base.lhs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libraries/base/GHC/Base.lhs b/libraries/base/GHC/Base.lhs
index 8b51c07..f9d01b5 100644
--- a/libraries/base/GHC/Base.lhs
+++ b/libraries/base/GHC/Base.lhs
@@ -788,6 +788,9 @@ augment g xs = g (:) xs
 "foldr/single"  forall k z x. foldr k z [x] = k x z
 "foldr/nil"     forall k z.   foldr k z []  = z
 
+"foldr/cons/build" forall k z x (g::forall b. (a->b->b) -> b -> b) .
+                           foldr k z (x:build g) = k x (g k z)
+
 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
                        (h::forall b. (a->b->b) -> b -> b) .
                        augment g (build h) = build (\c n -> g c (h c n))