From: simonpj <unknown>
Date: Fri, 20 Jul 2001 10:08:56 +0000 (+0000)
Subject: [project @ 2001-07-20 10:08:56 by simonpj]
X-Git-Tag: Approximately_9120_patches~1497
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=debd4f60f37ca2658f3470a343476542253760ab;hp=98a74c9da8b10a3ba8fa2c261c2e26970c56a811;p=ghc-hetmet.git

[project @ 2001-07-20 10:08:56 by simonpj]
--------------------------------------------
	Hack around an infelicity in the simplifier
	-------------------------------------------

Use 3 iterations of the simplifier (instead of the previous 2)
because otherwise we land up with huge dead expressions.
Reason: an infelicity in the simpifier.

      let k = BIG in foldr k z xs
 ==>  let k = BIG in letrec go = \xs -> ...(k x).... in go xs
 ==>  let k = BIG in letrec go = \xs -> ...(BIG x).... in go xs
 Don't stop now!


I couldn't see an easy way to make the simplifier avoid this
big intermediate, so I hacked round it like this.
---

diff --git a/ghc/compiler/main/DriverState.hs b/ghc/compiler/main/DriverState.hs
index e9e8aec..75f2cea 100644
--- a/ghc/compiler/main/DriverState.hs
+++ b/ghc/compiler/main/DriverState.hs
@@ -1,5 +1,5 @@
 -----------------------------------------------------------------------------
--- $Id: DriverState.hs,v 1.49 2001/07/17 15:28:30 simonpj Exp $
+-- $Id: DriverState.hs,v 1.50 2001/07/20 10:08:56 simonpj Exp $
 --
 -- Settings for the driver
 --
@@ -243,9 +243,17 @@ buildCoreToDo = do
 	]),
 
 	CoreDoSimplify (isAmongSimpl [
-	   MaxSimplifierIterations 2
+	   MaxSimplifierIterations 3
 		-- No -finline-phase: allow all Ids to be inlined now
 		-- This gets foldr inlined before strictness analysis
+		--
+		-- At least 3 iterations because otherwise we land up with
+		-- huge dead expressions because of an infelicity in the 
+		-- simpifier.   
+		--	let k = BIG in foldr k z xs
+		-- ==>  let k = BIG in letrec go = \xs -> ...(k x).... in go xs
+		-- ==>  let k = BIG in letrec go = \xs -> ...(BIG x).... in go xs
+		-- Don't stop now!
 	]),
 
 	if cpr        then CoreDoCPResult   else CoreDoNothing,