From: simonpj <unknown>
Date: Tue, 2 Jan 2001 16:42:10 +0000 (+0000)
Subject: [project @ 2001-01-02 16:42:10 by simonpj]
X-Git-Tag: Approximately_9120_patches~2990
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=ba56dcc42c4ea2fe0864360f7eec046a87383505;p=ghc-hetmet.git

[project @ 2001-01-02 16:42:10 by simonpj]
Add a necessary isUnliftedType to completeBinding (coerce case)
---

diff --git a/ghc/compiler/simplCore/Simplify.lhs b/ghc/compiler/simplCore/Simplify.lhs
index f15edf8..23f6f93 100644
--- a/ghc/compiler/simplCore/Simplify.lhs
+++ b/ghc/compiler/simplCore/Simplify.lhs
@@ -544,7 +544,7 @@ completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
     thing_inside
 
   | Note coercion@(Coerce _ inner_ty) inner_rhs <- new_rhs,
-    not trivial_rhs
+    not trivial_rhs && not (isUnLiftedType inner_ty)
 	-- x = coerce t e  ==>  c = e; x = inline_me (coerce t c)
 	-- Now x can get inlined, which moves the coercion
 	-- to the usage site.  This is a bit like worker/wrapper stuff,
@@ -558,6 +558,16 @@ completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
 	-- will inline x.  
 	-- Also the full-blown w/w thing isn't set up for non-functions
 	--
+	-- The (not (isUnLiftedType inner_ty)) avoids the nasty case of
+	--	x::Int = coerce Int Int# (foo y)
+	-- ==>
+	--	v::Int# = foo y
+	--	x::Int  = coerce Int Int# v
+	-- which would be bogus because then v will be evaluated strictly.
+	-- How can this arise?  Via 
+	--	x::Int = case (foo y) of { ... }
+	-- followed by case elimination.
+	--
 	-- The inline_me note is so that the simplifier doesn't 
 	-- just substitute c back inside x's rhs!  (Typically, x will
 	-- get substituted away, but not if it's exported.)