[commit: ghc] master: make the change to go_pap suggested in #4978. According to nofib, one (f43bede)

[Simon Marlow]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/f43bedeef3ecdf4d037a2484a0f0a3672ab60299

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

commit f43bedeef3ecdf4d037a2484a0f0a3672ab60299
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Tue May 24 13:18:55 2011 +0100

    make the change to go_pap suggested in #4978.  According to nofib, one
    program is improved quite dramatically (fft2 30% less allocation), and
    everything else was unchanged.

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

 compiler/coreSyn/CoreUtils.lhs |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs
index a0a229f..4146b62 100644
--- a/compiler/coreSyn/CoreUtils.lhs
+++ b/compiler/coreSyn/CoreUtils.lhs
@@ -589,11 +589,9 @@ exprIsCheap' good_app other_expr 	-- Applications and variables
     go _ _ = False
  
     --------------
-    go_pap args = all exprIsTrivial args
- 	-- For constructor applications and primops, check that all
- 	-- the args are trivial.  We don't want to treat as cheap, say,
- 	-- 	(1:2:3:4:5:[])
- 	-- We'll put up with one constructor application, but not dozens
+    go_pap args = all (exprIsCheap' good_app) args
+        -- Used to be "all exprIsTrivial args" due to concerns about
+        -- duplicating nested constructor applications, but see #4978.
  	
     --------------
     go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args