diff options
Diffstat (limited to 'compiler/GHC/Core.hs')
| -rw-r--r-- | compiler/GHC/Core.hs | 41 |
1 files changed, 28 insertions, 13 deletions
diff --git a/compiler/GHC/Core.hs b/compiler/GHC/Core.hs index 16b428cca4..ad1d87feae 100644 --- a/compiler/GHC/Core.hs +++ b/compiler/GHC/Core.hs @@ -43,7 +43,7 @@ module GHC.Core ( -- ** Simple 'Expr' access functions and predicates bindersOf, bindersOfBinds, rhssOfBind, rhssOfAlts, collectBinders, collectTyBinders, collectTyAndValBinders, - collectNBinders, + collectNBinders, collectNValBinders_maybe, collectArgs, stripNArgs, collectArgsTicks, flattenBinds, collectFunSimple, @@ -746,17 +746,18 @@ Join points must follow these invariants: the binder. Reason: if we want to push a continuation into the RHS we must push it into the unfolding as well. - 2b. The Arity (in the IdInfo) of a join point is the number of value - binders in the top n lambdas, where n is the join arity. + 2b. The Arity (in the IdInfo) of a join point varies independently of the + join-arity. For example, we could have + j x = case x of { T -> \y.y; F -> \y.3 } + Its join-arity is 1, but its idArity is 2; and we do not eta-expand + join points: see Note [Do not eta-expand join points] in + GHC.Core.Opt.Simplify.Utils. - So arity <= join arity; the former counts only value binders - while the latter counts all binders. - e.g. Suppose $j has join arity 1 - let j = \x y. e in case x of { A -> j 1; B -> j 2 } - Then its ordinary arity is also 1, not 2. + Allowing the idArity to be bigger than the join-arity is + important in arityType; see GHC.Core.Opt.Arity + Note [Arity for recursive join bindings] - The arity of a join point isn't very important; but short of setting - it to zero, it is helpful to have an invariant. E.g. #17294. + Historical note: see #17294. 3. If the binding is recursive, then all other bindings in the recursive group must also be join points. @@ -1973,9 +1974,11 @@ collectBinders :: Expr b -> ([b], Expr b) collectTyBinders :: CoreExpr -> ([TyVar], CoreExpr) collectValBinders :: CoreExpr -> ([Id], CoreExpr) collectTyAndValBinders :: CoreExpr -> ([TyVar], [Id], CoreExpr) --- | Strip off exactly N leading lambdas (type or value). Good for use with --- join points. -collectNBinders :: Int -> Expr b -> ([b], Expr b) + +-- | Strip off exactly N leading lambdas (type or value). +-- Good for use with join points. +-- Panic if there aren't enough +collectNBinders :: JoinArity -> Expr b -> ([b], Expr b) collectBinders expr = go [] expr @@ -2008,6 +2011,18 @@ collectNBinders orig_n orig_expr go n bs (Lam b e) = go (n-1) (b:bs) e go _ _ _ = pprPanic "collectNBinders" $ int orig_n +-- | Strip off exactly N leading value lambdas +-- returning all the binders found up to that point +-- Return Nothing if there aren't enough +collectNValBinders_maybe :: Arity -> CoreExpr -> Maybe ([Var], CoreExpr) +collectNValBinders_maybe orig_n orig_expr + = go orig_n [] orig_expr + where + go 0 bs expr = Just (reverse bs, expr) + go n bs (Lam b e) | isId b = go (n-1) (b:bs) e + | otherwise = go n (b:bs) e + go _ _ _ = Nothing + -- | Takes a nested application expression and returns the function -- being applied and the arguments to which it is applied collectArgs :: Expr b -> (Expr b, [Arg b]) |