Repository : ssh://darcs.haskell.org//srv/darcs/ghc On branch : new-demand-to-merge
http://hackage.haskell.org/trac/ghc/changeset/7b64905a38ffed5e2d57d9c2f68f6be286a80f93 >--------------------------------------------------------------- commit 7b64905a38ffed5e2d57d9c2f68f6be286a80f93 Author: Simon Peyton Jones <simo...@microsoft.com> Date: Wed Jan 9 17:44:27 2013 +0000 Make CSE work for case expressions too See Note [CSE for case expressions] in CSE. Seldom makes a difference, but a very simple change. >--------------------------------------------------------------- compiler/simplCore/CSE.lhs | 15 +++++++++++---- 1 files changed, 11 insertions(+), 4 deletions(-) diff --git a/compiler/simplCore/CSE.lhs b/compiler/simplCore/CSE.lhs index 18c0178..55976a2 100644 --- a/compiler/simplCore/CSE.lhs +++ b/compiler/simplCore/CSE.lhs @@ -170,6 +170,12 @@ Now CSE may transform to But the WorkerInfo for f still says $wf, which is now dead! This won't happen now that we don't look inside INLINEs (which wrappers are). +Note [CSE for case expressions] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + case f x of y { pat -> ...let y = f x in ... } +Then we can CSE the inner (f x) to y. In fact 'case' is like a strict +let-binding, and we can use cseRhs for dealing with the scrutinee. %************************************************************************ %* * @@ -226,7 +232,7 @@ cseExpr env (Coercion c) = Coercion (substCo (csEnvSubst env) c) cseExpr _ (Lit lit) = Lit lit cseExpr env (Var v) = lookupSubst env v cseExpr env (App f a) = App (cseExpr env f) (tryForCSE env a) -cseExpr env (Tick t e) = Tick t (cseExpr env e) +cseExpr env (Tick t e) = Tick t (cseExpr env e) cseExpr env (Cast e co) = Cast (cseExpr env e) (substCo (csEnvSubst env) co) cseExpr env (Lam b e) = let (env', b') = addBinder env b in Lam b' (cseExpr env' e) @@ -234,9 +240,10 @@ cseExpr env (Let bind e) = let (env', bind') = cseBind env bind in Let bind' (cseExpr env' e) cseExpr env (Case scrut bndr ty alts) = Case scrut' bndr'' ty alts' where - alts' = cseAlts env' scrut' bndr bndr'' alts - scrut' = tryForCSE env scrut - (env', bndr') = addBinder env bndr + alts' = cseAlts env2 scrut' bndr bndr'' alts + (env1, bndr') = addBinder env bndr + (env2, scrut') = cseRhs env1 (bndr', scrut) + -- Note [CSE for case expressions] bndr'' = zapIdOccInfo bndr' -- The swizzling from Note [Case binders 2] may -- cause a dead case binder to be alive, so we _______________________________________________ Cvs-ghc mailing list Cvs-ghc@haskell.org http://www.haskell.org/mailman/listinfo/cvs-ghc
