hashExpr,
-- * Equality
- cheapEqExpr,
+ cheapEqExpr, eqExpr, eqExprX,
-- * Manipulating data constructors and types
applyTypeToArgs, applyTypeToArg,
%* *
%************************************************************************
-Note [exprIsCheap]
-~~~~~~~~~~~~~~~~~~
+Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
+~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
@exprIsCheap@ looks at a Core expression and returns \tr{True} if
it is obviously in weak head normal form, or is cheap to get to WHNF.
[Note that that's not the same as exprIsDupable; an expression might be
Notice that a variable is considered 'cheap': we can push it inside a lambda,
because sharing will make sure it is only evaluated once.
+Note [exprIsCheap and exprIsHNF]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Note that exprIsHNF does not imply exprIsCheap. Eg
+ let x = fac 20 in Just x
+This responds True to exprIsHNF (you can discard a seq), but
+False to exprIsCheap.
+
\begin{code}
exprIsCheap :: CoreExpr -> Bool
exprIsCheap = exprIsCheap' isCheapApp
-- there is only dictionary selection (no construction) involved
exprIsCheap' good_app (Let (NonRec x _) e)
- | isUnLiftedType (idType x) = exprIsCheap' good_app e
- | otherwise = False
+ | isUnLiftedType (idType x) = exprIsCheap' good_app e
+ | otherwise = False
-- Strict lets always have cheap right hand sides,
-- and do no allocation, so just look at the body
-- Non-strict lets do allocation so we don't treat them as cheap
+ -- See also
exprIsCheap' good_app other_expr -- Applications and variables
= go other_expr []
-- Precisely, it returns @True@ iff:
--
-- * The expression guarantees to terminate,
---
-- * soon,
---
-- * without raising an exception,
---
-- * without causing a side effect (e.g. writing a mutable variable)
--
-- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
&& not (isTickBoxOp v)
exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
+
+exprOkForSpeculation (Case e _ _ alts)
+ = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
+ && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
+
exprOkForSpeculation other_expr
= case collectArgs other_expr of
(Var f, args) -> spec_ok (idDetails f) args
isDivOp _ = False
\end{code}
+Note [exprOkForSpeculation: case expressions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It's always sound for exprOkForSpeculation to return False, and we
+don't want it to take too long, so it bales out on complicated-looking
+terms. Notably lets, which can be stacked very deeply; and in any
+case the argument of exprOkForSpeculation is usually in a strict context,
+so any lets will have been floated away.
+
+However, we keep going on case-expressions. An example like this one
+showed up in DPH code:
+ foo :: Int -> Int
+ foo 0 = 0
+ foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
+
+If exprOkForSpeculation doesn't look through case expressions, you get this:
+ T.$wfoo =
+ \ (ww :: GHC.Prim.Int#) ->
+ case ww of ds {
+ __DEFAULT -> case (case <# ds 5 of _ {
+ GHC.Bool.False -> lvl1;
+ GHC.Bool.True -> lvl})
+ of _ { __DEFAULT ->
+ T.$wfoo (GHC.Prim.-# ds_XkE 1) };
+ 0 -> 0
+ }
+
+The inner case is redundant, and should be nuked.
+
+
%************************************************************************
%* *
exprIsHNF, exprIsConLike
%************************************************************************
\begin{code}
--- Note [exprIsHNF]
+-- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
-- ~~~~~~~~~~~~~~~~
-- | exprIsHNF returns true for expressions that are certainly /already/
-- evaluated to /head/ normal form. This is used to decide whether it's ok
= e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
cheapEqExpr _ _ = False
+\end{code}
+\begin{code}
exprIsBig :: Expr b -> Bool
-- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
exprIsBig (Lit _) = False
exprIsBig _ = True
\end{code}
+\begin{code}
+eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
+-- Compares for equality, modulo alpha
+eqExpr in_scope e1 e2
+ = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
+ where
+ id_unf _ = noUnfolding -- Don't expand
+\end{code}
+
+\begin{code}
+eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
+-- ^ Compares expressions for equality, modulo alpha.
+-- Does /not/ look through newtypes or predicate types
+-- Used in rule matching, and also CSE
+
+eqExprX id_unfolding_fun env e1 e2
+ = go env e1 e2
+ where
+ go env (Var v1) (Var v2)
+ | rnOccL env v1 == rnOccR env v2
+ = True
+
+ -- The next two rules expand non-local variables
+ -- C.f. Note [Expanding variables] in Rules.lhs
+ -- and Note [Do not expand locally-bound variables] in Rules.lhs
+ go env (Var v1) e2
+ | not (locallyBoundL env v1)
+ , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
+ = go (nukeRnEnvL env) e1' e2
+
+ go env e1 (Var v2)
+ | not (locallyBoundR env v2)
+ , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
+ = go (nukeRnEnvR env) e1 e2'
+
+ go _ (Lit lit1) (Lit lit2) = lit1 == lit2
+ go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
+ go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
+ go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
+ go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
+
+ go env (Lam b1 e1) (Lam b2 e2)
+ = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
+ && go (rnBndr2 env b1 b2) e1 e2
+
+ go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
+ = go env r1 r2 -- No need to check binder types, since RHSs match
+ && go (rnBndr2 env v1 v2) e1 e2
+
+ go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
+ = all2 (go env') rs1 rs2 && go env' e1 e2
+ where
+ (bs1,rs1) = unzip ps1
+ (bs2,rs2) = unzip ps2
+ env' = rnBndrs2 env bs1 bs2
+
+ go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
+ = go env e1 e2
+ && tcEqTypeX env (idType b1) (idType b2)
+ && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
+
+ go _ _ _ = False
+
+ -----------
+ go_alt env (c1, bs1, e1) (c2, bs2, e2)
+ = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
+
+ -----------
+ go_note (SCC cc1) (SCC cc2) = cc1 == cc2
+ go_note (CoreNote s1) (CoreNote s2) = s1 == s2
+ go_note _ _ = False
+\end{code}
+
+Auxiliary functions
+
+\begin{code}
+locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
+locallyBoundL rn_env v = inRnEnvL rn_env v
+locallyBoundR rn_env v = inRnEnvR rn_env v
+\end{code}
%************************************************************************
projects / ghc-hetmet.git / blobdiff