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/codeGen/StgCmmMonad.hs b/compiler/codeGen/StgCmmMonad.hs
index 1a708670b3..9ddd8a3985 100644
--- a/compiler/codeGen/StgCmmMonad.hs
+++ b/compiler/codeGen/StgCmmMonad.hs
@@ -632,7 +632,7 @@ forkAlts branch_fcodes
                                       , cgs_hp_usg = cgs_hp_usg state }
               (_us, results) = mapAccumL compile us branch_fcodes
               (branch_results, branch_out_states) = unzip results
-        ; setState $ foldl stateIncUsage state branch_out_states
+        ; setState $ foldl' stateIncUsage state branch_out_states
                 -- NB foldl.  state is the *left* argument to stateIncUsage
         ; return branch_results }