Replace most occurences of foldl with foldl'.

This patch adds foldl' to GhcPrelude and changes must occurences
of foldl to foldl'. This leads to better performance especially
for quick builds where GHC does not perform strictness analysis.

It does change strictness behaviour when we use foldl' to turn
a argument list into function applications. But this is only a
drawback if code looks ONLY at the last argument but not at the first.
And as the benchmarks show leads to fewer allocations in practice
at O2.

Compiler performance for Nofib:

O2 Allocations:
        -1 s.d.                -----            -0.0%
        +1 s.d.                -----            -0.0%
        Average                -----            -0.0%

O2 Compile Time:
        -1 s.d.                -----            -2.8%
        +1 s.d.                -----            +1.3%
        Average                -----            -0.8%

O0 Allocations:
        -1 s.d.                -----            -0.2%
        +1 s.d.                -----            -0.1%
        Average                -----            -0.2%

Test Plan: ci

Reviewers: goldfire, bgamari, simonmar, tdammers, monoidal

Reviewed By: bgamari, monoidal

Subscribers: tdammers, rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4929

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/typecheck/TcGenFunctor.hs b/compiler/typecheck/TcGenFunctor.hs
index 036c6511d3..8310cf9500 100644
--- a/compiler/typecheck/TcGenFunctor.hs
+++ b/compiler/typecheck/TcGenFunctor.hs
@@ -940,7 +940,7 @@ gen_Traversable_binds loc tycon
         mkApCon con [] = nlHsApps pure_RDR [con]
         mkApCon con [x] = nlHsApps fmap_RDR [con,x]
         mkApCon con (x1:x2:xs) =
-            foldl appAp (nlHsApps liftA2_RDR [con,x1,x2]) xs
+            foldl' appAp (nlHsApps liftA2_RDR [con,x1,x2]) xs
           where appAp x y = nlHsApps ap_RDR [x,y]
 
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