diff options
Diffstat (limited to 'compiler/GHC/Core/Utils.hs')
| -rw-r--r-- | compiler/GHC/Core/Utils.hs | 37 |
1 files changed, 26 insertions, 11 deletions
diff --git a/compiler/GHC/Core/Utils.hs b/compiler/GHC/Core/Utils.hs index baefb7712b..03e2ecee55 100644 --- a/compiler/GHC/Core/Utils.hs +++ b/compiler/GHC/Core/Utils.hs @@ -38,7 +38,7 @@ module GHC.Core.Utils ( diffBinds, -- * Lambdas and eta reduction - tryEtaReduce, + tryEtaReduce, canEtaReduceToArity, -- * Manipulating data constructors and types exprToType, exprToCoercion_maybe, @@ -2448,17 +2448,10 @@ tryEtaReduce bndrs body ok_fun _fun = False --------------- - ok_fun_id fun = -- There are arguments to reduce + ok_fun_id fun = -- There are arguments to reduce... fun_arity fun >= incoming_arity && - -- We always want args for join points so - -- we should never eta-reduce to a trivial expression. - -- See Note [Invariants on join points] in GHC.Core, and #20599 - not (isJoinId fun) && - -- And the function doesn't require visible arguments as part of - -- it's calling convention. See Note [Strict Worker Ids] - idCbvMarkArity fun == 0 - - + -- ... and the function can be eta reduced to arity 0 + canEtaReduceToArity fun 0 0 --------------- fun_arity fun -- See Note [Arity care] | isLocalId fun @@ -2505,6 +2498,28 @@ tryEtaReduce bndrs body ok_arg _ _ _ _ = Nothing +-- | Can we eta-reduce the given function to the specified arity? +-- See Note [Eta reduction conditions]. +canEtaReduceToArity :: Id -> JoinArity -> Arity -> Bool +canEtaReduceToArity fun dest_join_arity dest_arity = + not $ + hasNoBinding fun + -- Don't undersaturate functions with no binding. + + || ( isJoinId fun && dest_join_arity < idJoinArity fun ) + -- Don't undersaturate join points. + -- See Note [Invariants on join points] in GHC.Core, and #20599 + + || ( dest_arity < idCbvMarkArity fun ) + -- Don't undersaturate StrictWorkerIds. + -- See Note [Strict Worker Ids] in GHC.CoreToStg.Prep. + + || isLinearType (idType fun) + -- Don't perform eta reduction on linear types. + -- If `f :: A %1-> B` and `g :: A -> B`, + -- then `g x = f x` is OK but `g = f` is not. + -- See Note [Eta reduction conditions]. + {- Note [Eta reduction of an eval'd function] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |