From f43bedeef3ecdf4d037a2484a0f0a3672ab60299 Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Tue, 24 May 2011 13:18:55 +0100
Subject: [PATCH] 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 | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs
index a0a229f6c668..4146b621e158 100644
--- a/compiler/coreSyn/CoreUtils.lhs
+++ b/compiler/coreSyn/CoreUtils.lhs
@@ -589,12 +589,10 @@ 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
-- In principle we should worry about primops
--
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