diff options
| -rw-r--r-- | compiler/GHC/Core/Opt/Simplify/Utils.hs | 22 |
1 files changed, 14 insertions, 8 deletions
diff --git a/compiler/GHC/Core/Opt/Simplify/Utils.hs b/compiler/GHC/Core/Opt/Simplify/Utils.hs index bca029783c..cb99a16acc 100644 --- a/compiler/GHC/Core/Opt/Simplify/Utils.hs +++ b/compiler/GHC/Core/Opt/Simplify/Utils.hs @@ -927,8 +927,9 @@ updModeForStableUnfoldings :: Activation -> SimplMode -> SimplMode -- See Note [The environments of the Simplify pass] updModeForStableUnfoldings unf_act current_mode = current_mode { sm_phase = phaseFromActivation unf_act + , sm_eta_expand = False , sm_inline = True } - -- sm_eta_expand: see Historical-note [No eta expansion in stable unfoldings] + -- sm_eta_expand: see Note [Eta expansion in stable unfoldings and rules] -- sm_rules: just inherit; sm_rules might be "off" -- because of -fno-enable-rewrite-rules where @@ -993,11 +994,14 @@ we don't want to swizzle this to (\x. blah) |> (Refl xty `FunCo` CoVar cv) So we switch off cast swizzling in updModeForRules. -Historical-note [No eta expansion in stable unfoldings] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -This Note is no longer relevant because the specialiser has improved. -See Note [Account for casts in binding] in GHC.Core.Opt.Specialise. -So we do not override sm_eta_expand in updModeForStableUnfoldings. +Note [Eta expansion in stable unfoldings and rules] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +SPJ Jul 22: whether or not eta-expansion is switched on in a stable +unfolding, or the RHS of a RULE, seems to be a bit moot. But switching +it on adds clutter, so I'm experimenting with switching off +eta-expansion in such places. + +In the olden days, we really /wanted/ to switch it off. Old note: If we have a stable unfolding f :: Ord a => a -> IO () @@ -1007,11 +1011,13 @@ So we do not override sm_eta_expand in updModeForStableUnfoldings. f :: Ord a => a -> IO () -- Unfolding template -- = (/\a \(d:Ord a) (x:a) (eta:State#). bla eta) |> co - because not specialisation of the overloading doesn't work properly + because now specialisation of the overloading doesn't work properly (see Note [Specialisation shape] in GHC.Core.Opt.Specialise), #9509. So we disable eta-expansion in stable unfoldings. - End of Historical Note +But this old note is no longer relevant because the specialiser has +improved: see Note [Account for casts in binding] in +GHC.Core.Opt.Specialise. So we seem to have a free choice. Note [Inlining in gentle mode] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |