X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FSimplEnv.lhs;fp=compiler%2FsimplCore%2FSimplEnv.lhs;h=70e0fa11491c6bed378739750e9803cf97824fd5;hb=3b896bc3a6fbc19ee311849aed046edcd75dca62;hp=3cdbb3291dd093ff30be54b2736966eb1fe70dae;hpb=0ac253aac15a6d5bcfa54be310531203a5456a0a;p=ghc-hetmet.git

diff --git a/compiler/simplCore/SimplEnv.lhs b/compiler/simplCore/SimplEnv.lhs
index 3cdbb32..70e0fa1 100644
--- a/compiler/simplCore/SimplEnv.lhs
+++ b/compiler/simplCore/SimplEnv.lhs
@@ -284,10 +284,6 @@ setSubstEnv env tvs ids = env { seTvSubst = tvs, seIdSubst = ids }
 
 mkContEx :: SimplEnv -> InExpr -> SimplSR
 mkContEx (SimplEnv { seTvSubst = tvs, seIdSubst = ids }) e = ContEx tvs ids e
-
-isEmptySimplSubst :: SimplEnv -> Bool
-isEmptySimplSubst (SimplEnv { seTvSubst = tvs, seIdSubst = ids })
-  = isEmptyVarEnv tvs && isEmptyVarEnv ids
 \end{code}
 
 
@@ -713,8 +709,8 @@ mkCoreSubst (SimplEnv { seInScope = in_scope, seTvSubst = tv_env, seIdSubst = id
     fiddle (ContEx tv id e) = CoreSubst.substExpr (mk_subst tv id) e
 
 substExpr :: SimplEnv -> CoreExpr -> CoreExpr
-substExpr env expr
-  | isEmptySimplSubst env = expr
-  | otherwise	          = CoreSubst.substExpr (mkCoreSubst env) expr
+substExpr env expr = CoreSubst.substExpr (mkCoreSubst env) expr
+  -- Do *not* short-cut in the case of an empty substitution
+  -- See CoreSubst: Note [Extending the Subst]
 \end{code}