[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 (file)
--- 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,