[commit: ghc] master: cleanup: drop 11 years old performance hack (cdbb9da)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/cdbb9da7a1330366678c4e29d11a48e591c1ac1e/ghc

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

commit cdbb9da7a1330366678c4e29d11a48e591c1ac1e
Author: Sergei Trofimovich <siarheit at google.com>
Date:   Sun Sep 4 22:08:27 2016 +0100

    cleanup: drop 11 years old performance hack
    
    The 'return () >>' hack was added in commit
        commit ac88f113abdec1edbffb6d2f97323e81f82908e7
        Date:   Tue Jul 26 12:14:03 2005 +0000
    
    Nowadays it has no effect on generated Core on -O1/-O2
    and slightly bloats Core on -O0.
    
    Signed-off-by: Sergei Trofimovich <siarheit at google.com>


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

cdbb9da7a1330366678c4e29d11a48e591c1ac1e
 compiler/utils/Pretty.hs | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/compiler/utils/Pretty.hs b/compiler/utils/Pretty.hs
index 9849032..5b025d5 100644
--- a/compiler/utils/Pretty.hs
+++ b/compiler/utils/Pretty.hs
@@ -1018,9 +1018,6 @@ hPutLitString handle a l = if l == 0
 --     and async exception-safe.  We only have a single thread and don't
 --     care about exceptions, so we add a layer of fast buffering
 --     over the Handle interface.
---
--- (3) a few hacks in layLeft below to convince GHC to generate the right
---     code.
 
 printLeftRender :: Handle -> Doc -> IO ()
 printLeftRender hdl doc = do
@@ -1031,14 +1028,11 @@ printLeftRender hdl doc = do
 bufLeftRender :: BufHandle -> Doc -> IO ()
 bufLeftRender b doc = layLeft b (reduceDoc doc)
 
--- HACK ALERT!  the "return () >>" below convinces GHC to eta-expand
--- this function with the IO state lambda.  Otherwise we end up with
--- closures in all the case branches.
 layLeft :: BufHandle -> Doc -> IO ()
 layLeft b _ | b `seq` False  = undefined -- make it strict in b
 layLeft _ NoDoc              = error "layLeft: NoDoc"
-layLeft b (Union p q)        = return () >> layLeft b (first p q)
-layLeft b (Nest _ p)         = return () >> layLeft b p
+layLeft b (Union p q)        = layLeft b (first p q)
+layLeft b (Nest _ p)         = layLeft b p
 layLeft b Empty              = bPutChar b '\n'
 layLeft b (NilAbove p)       = bPutChar b '\n' >> layLeft b p
 layLeft b (TextBeside s _ p) = put b s >> layLeft b p