-- ** Substituting and cloning binders
substBndr, substBndrs, substRecBndrs,
- cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs
+ cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs,
+
+ -- ** Simple expression optimiser
+ simpleOptExpr
) where
#include "HsVersions.h"
import CoreSyn
import CoreFVs
import CoreUtils
+import OccurAnal( occurAnalyseExpr )
import qualified Type
import Type ( Type, TvSubst(..), TvSubstEnv )
| isId fv = exprFreeVars (lookupIdSubst subst fv)
| otherwise = Type.tyVarsOfType (lookupTvSubst subst fv)
\end{code}
+
+%************************************************************************
+%* *
+ The Very Simple Optimiser
+%* *
+%************************************************************************
+
+\begin{code}
+simpleOptExpr :: CoreExpr -> CoreExpr
+-- Return an occur-analysed and slightly optimised expression
+-- The optimisation is very straightforward: just
+-- inline non-recursive bindings that are used only once,
+-- or where the RHS is trivial
+
+simpleOptExpr expr
+ = go init_subst (occurAnalyseExpr expr)
+ where
+ init_subst = mkEmptySubst (mkInScopeSet (exprFreeVars expr))
+ -- It's potentially to make a proper in-scope set
+ -- Consider let x = ..y.. in \y. ...x...
+ -- Then we should remember to clone y before substituting
+ -- for x. It's very unlikely to occur, because we probably
+ -- won't *be* substituting for x if it occurs inside a
+ -- lambda.
+ --
+ -- It's a bit painful to call exprFreeVars, because it makes
+ -- three passes instead of two (occ-anal, and go)
+
+ go subst (Var v) = lookupIdSubst subst v
+ go subst (App e1 e2) = App (go subst e1) (go subst e2)
+ go subst (Type ty) = Type (substTy subst ty)
+ go _ (Lit lit) = Lit lit
+ go subst (Note note e) = Note note (go subst e)
+ go subst (Cast e co) = Cast (go subst e) (substTy subst co)
+ go subst (Let bind body) = go_bind subst bind body
+ go subst (Lam bndr body) = Lam bndr' (go subst' body)
+ where
+ (subst', bndr') = substBndr subst bndr
+
+ go subst (Case e b ty as) = Case (go subst e) b'
+ (substTy subst ty)
+ (map (go_alt subst') as)
+ where
+ (subst', b') = substBndr subst b
+
+
+ ----------------------
+ go_alt subst (con, bndrs, rhs) = (con, bndrs', go subst' rhs)
+ where
+ (subst', bndrs') = substBndrs subst bndrs
+
+ ----------------------
+ go_bind subst (Rec prs) body = Let (Rec (bndrs' `zip` rhss'))
+ (go subst' body)
+ where
+ (bndrs, rhss) = unzip prs
+ (subst', bndrs') = substRecBndrs subst bndrs
+ rhss' = map (go subst') rhss
+
+ go_bind subst (NonRec b r) body = go_nonrec subst b (go subst r) body
+
+ ----------------------
+ go_nonrec subst b (Type ty') body
+ | isTyVar b = go (extendTvSubst subst b ty') body
+ -- let a::* = TYPE ty in <body>
+ go_nonrec subst b r' body
+ | isId b -- let x = e in <body>
+ , exprIsTrivial r' || safe_to_inline (idOccInfo b)
+ = go (extendIdSubst subst b r') body
+ go_nonrec subst b r' body
+ = Let (NonRec b' r') (go subst' body)
+ where
+ (subst', b') = substBndr subst b
+
+ ----------------------
+ -- Unconditionally safe to inline
+ safe_to_inline :: OccInfo -> Bool
+ safe_to_inline IAmDead = True
+ safe_to_inline (OneOcc in_lam one_br _) = not in_lam && one_br
+ safe_to_inline (IAmALoopBreaker {}) = False
+ safe_to_inline NoOccInfo = False
+\end{code}
projects / ghc-hetmet.git / blobdiff