Commit 6c9fae23 authored by Alexis King's avatar Alexis King Committed by Marge Bot
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Mark DataCon wrappers CONLIKE

Now that DataCon wrappers don’t inline until phase 0 (see commit
b78cc64e), it’s important that
case-of-known-constructor and RULE matching be able to see saturated
applications of DataCon wrappers in unfoldings. Making them conlike is a
natural way to do it, since they are, in fact, precisely the sort of
thing the CONLIKE pragma exists to solve.

Fixes #18012.

This also bumps the version of the parsec submodule to incorporate a
patch that avoids a metric increase on the haddock perf tests. The
increase was not really a flaw in this patch, as parsec was implicitly
relying on inlining heuristics. The patch to parsec just adds some
INLINABLE pragmas, and we get a nice performance bump out of it (well
beyond the performance we lost from this patch).

Metric Decrease:
    T12234
    WWRec
    haddock.Cabal
    haddock.base
    haddock.compiler
parent 401f7bb3
Pipeline #18458 passed with stages
in 405 minutes and 53 seconds
......@@ -889,6 +889,10 @@ And now we have a known-constructor MkT that we can return.
Notice that both (2) and (3) require exprIsConApp_maybe to gather and return
a bunch of floats, both let and case bindings.
Note that this strategy introduces some subtle scenarios where a data-con
wrapper can be replaced by a data-con worker earlier than we’d like, see
Note [exprIsConApp_maybe for data-con wrappers: tricky corner].
Note [beta-reduction in exprIsConApp_maybe]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The unfolding a definition (_e.g._ a let-bound variable or a datacon wrapper) is
......@@ -949,6 +953,60 @@ exprIsConApp_maybe does not return Just) then nothing happens, and nothing
will happen the next time either.
See test T16254, which checks the behavior of newtypes.
Note [exprIsConApp_maybe for data-con wrappers: tricky corner]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Generally speaking
* exprIsConApp_maybe honours the inline phase; that is, it does not look
inside the unfolding for an Id unless its unfolding is active in this phase.
That phase-sensitivity is expressed in the InScopeEnv (specifically, the
IdUnfoldingFun component of the InScopeEnv) passed to exprIsConApp_maybe.
* Data-constructor wrappers are active only in phase 0 (the last phase);
see Note [Activation for data constructor wrappers] in GHC.Types.Id.Make.
On the face of it that means that exprIsConApp_maybe won't look inside data
constructor wrappers until phase 0. But that seems pretty Bad. So we cheat.
For data con wrappers we unconditionally look inside its unfolding, regardless
of phase, so that we get case-of-known-constructor to fire in every phase.
Perhaps unsurprisingly, this cheating can backfire. An example:
data T = C !A B
foo p q = let x = C e1 e2 in seq x $ f x
{-# RULE "wurble" f (C a b) = b #-}
In Core, the RHS of foo is
let x = $WC e1 e2 in case x of y { C _ _ -> f x }
and after doing a binder swap and inlining x, we have:
case $WC e1 e2 of y { C _ _ -> f y }
Case-of-known-constructor fires, but now we have to reconstruct a binding for
`y` (which was dead before the binder swap) on the RHS of the case alternative.
Naturally, we’ll use the worker:
case e1 of a { DEFAULT -> let y = C a e2 in f y }
and after inlining `y`, we have:
case e1 of a { DEFAULT -> f (C a e2) }
Now we might hope the "wurble" rule would fire, but alas, it will not: we have
replaced $WC with C, but the (desugared) rule matches on $WC! We weren’t
supposed to inline $WC yet for precisely that reason (see Note [Activation for
data constructor wrappers]), but our cheating in exprIsConApp_maybe came back to
bite us.
This is rather unfortunate, especially since this can happen inside stable
unfoldings as well as ordinary code (which really happened, see !3041). But
there is no obvious solution except to delay case-of-known-constructor on
data-con wrappers, and that cure would be worse than the disease.
This Note exists solely to document the problem.
-}
data ConCont = CC [CoreExpr] Coercion
......@@ -1033,7 +1091,8 @@ exprIsConApp_maybe (in_scope, id_unf) expr
-- Look through data constructor wrappers: they inline late (See Note
-- [Activation for data constructor wrappers]) but we want to do
-- case-of-known-constructor optimisation eagerly.
-- case-of-known-constructor optimisation eagerly (see Note
-- [exprIsConApp_maybe on data constructors with wrappers]).
| isDataConWrapId fun
, let rhs = uf_tmpl (realIdUnfolding fun)
= go (Left in_scope) floats rhs cont
......
......@@ -91,7 +91,7 @@ import GHC.Builtin.Types.Prim
import FastString
import Maybes
import ListSetOps ( minusList )
import GHC.Types.Basic ( Arity, isConLike )
import GHC.Types.Basic ( Arity )
import Util
import Pair
import Data.ByteString ( ByteString )
......@@ -1387,15 +1387,14 @@ isExpandableApp fn n_val_args
| isWorkFreeApp fn n_val_args = True
| otherwise
= case idDetails fn of
DataConWorkId {} -> True -- Actually handled by isWorkFreeApp
RecSelId {} -> n_val_args == 1 -- See Note [Record selection]
ClassOpId {} -> n_val_args == 1
PrimOpId {} -> False
_ | isBottomingId fn -> False
RecSelId {} -> n_val_args == 1 -- See Note [Record selection]
ClassOpId {} -> n_val_args == 1
PrimOpId {} -> False
_ | isBottomingId fn -> False
-- See Note [isExpandableApp: bottoming functions]
| isConLike (idRuleMatchInfo fn) -> True
| all_args_are_preds -> True
| otherwise -> False
| isConLikeId fn -> True
| all_args_are_preds -> True
| otherwise -> False
where
-- See if all the arguments are PredTys (implicit params or classes)
......
......@@ -768,7 +768,7 @@ idRuleMatchInfo :: Id -> RuleMatchInfo
idRuleMatchInfo id = inlinePragmaRuleMatchInfo (idInlinePragma id)
isConLikeId :: Id -> Bool
isConLikeId id = isDataConWorkId id || isConLike (idRuleMatchInfo id)
isConLikeId id = isConLike (idRuleMatchInfo id)
{-
---------------------------------
......
......@@ -510,19 +510,21 @@ mkDataConWorkId wkr_name data_con
alg_wkr_info = noCafIdInfo
`setArityInfo` wkr_arity
`setCprInfo` mkCprSig wkr_arity (dataConCPR data_con)
`setInlinePragInfo` wkr_inline_prag
`setUnfoldingInfo` evaldUnfolding -- Record that it's evaluated,
-- even if arity = 0
`setLevityInfoWithType` wkr_ty
-- NB: unboxed tuples have workers, so we can't use
-- setNeverLevPoly
wkr_inline_prag = defaultInlinePragma { inl_rule = ConLike }
wkr_arity = dataConRepArity data_con
----------- Workers for newtypes --------------
univ_tvs = dataConUnivTyVars data_con
arg_tys = dataConRepArgTys data_con -- Should be same as dataConOrigArgTys
nt_work_info = noCafIdInfo -- The NoCaf-ness is set by noCafIdInfo
`setArityInfo` 1 -- Arity 1
`setInlinePragInfo` alwaysInlinePragma
`setInlinePragInfo` dataConWrapperInlinePragma
`setUnfoldingInfo` newtype_unf
`setLevityInfoWithType` wkr_ty
id_arg1 = mkTemplateLocal 1 (head arg_tys)
......@@ -652,8 +654,8 @@ mkDataConRep dflags fam_envs wrap_name mb_bangs data_con
mk_dmd str | isBanged str = evalDmd
| otherwise = topDmd
wrap_prag = alwaysInlinePragma `setInlinePragmaActivation`
activeDuringFinal
wrap_prag = dataConWrapperInlinePragma
`setInlinePragmaActivation` activeDuringFinal
-- See Note [Activation for data constructor wrappers]
-- The wrapper will usually be inlined (see wrap_unf), so its
......@@ -763,6 +765,12 @@ mkDataConRep dflags fam_envs wrap_name mb_bangs data_con
; expr <- mk_rep_app prs (mkVarApps con_app rep_ids)
; return (unbox_fn expr) }
dataConWrapperInlinePragma :: InlinePragma
-- See Note [DataCon wrappers are conlike]
dataConWrapperInlinePragma = alwaysInlinePragma { inl_rule = ConLike
, inl_inline = Inline }
{- Note [Activation for data constructor wrappers]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Activation on a data constructor wrapper allows it to inline only in Phase
......@@ -784,6 +792,37 @@ the order of type argument could make previously working RULEs fail.
See also https://gitlab.haskell.org/ghc/ghc/issues/15840 .
Note [DataCon wrappers are conlike]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DataCon workers are clearly ConLike --- they are the “Con” in
“ConLike”, after all --- but what about DataCon wrappers? Should they
be marked ConLike, too?
Yes, absolutely! As described in Note [CONLIKE pragma] in
GHC.Types.Basic, isConLike influences GHC.Core.Utils.exprIsExpandable,
which is used by both RULE matching and the case-of-known-constructor
optimization. It’s crucial that both of those things can see
applications of DataCon wrappers:
* User-defined RULEs match on wrappers, not workers, so we might
need to look through an unfolding built from a DataCon wrapper to
determine if a RULE matches.
* Likewise, if we have something like
let x = $WC a b in ... case x of { C y z -> e } ...
we still want to apply case-of-known-constructor.
Therefore, it’s important that we consider DataCon wrappers conlike.
This is especially true now that we don’t inline DataCon wrappers
until the final simplifier phase; see Note [Activation for data
constructor wrappers].
For further reading, see:
* Note [Conlike is interesting] in GHC.Core.Op.Simplify.Utils
* Note [Lone variables] in GHC.Core.Unfold
* Note [exprIsConApp_maybe on data constructors with wrappers]
in GHC.Core.SimpleOpt
* #18012
Note [Bangs on imported data constructors]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
......
Subproject commit ee741870f028e036ab15ae6e2183f09b31e51ae2
Subproject commit ce416997e15438ca616667995660e123ef7e219d
......@@ -4,7 +4,7 @@ Result size of Tidy Core
= {terms: 63, types: 43, coercions: 1, joins: 0/0}
-- RHS size: {terms: 2, types: 4, coercions: 1, joins: 0/0}
T2431.$WRefl [InlPrag=INLINE[0]] :: forall a. a :~: a
T2431.$WRefl [InlPrag=INLINE[0] CONLIKE] :: forall a. a :~: a
[GblId[DataConWrapper],
Caf=NoCafRefs,
Cpr=m1,
......@@ -110,3 +110,6 @@ T2431.$tc'Refl
$tc'Refl2
1#
$krep3
......@@ -120,11 +120,11 @@ Rule fired: mkRule @(_, ()) (T18013a)
Rule fired: Class op fmap (BUILTIN)
Rule fired: mkRule @((), _) (T18013a)
Rule fired: Class op fmap (BUILTIN)
Rule fired: mkRule @(_, ()) (T18013a)
Rule fired: mkRule @((), _) (T18013a)
Rule fired: Class op fmap (BUILTIN)
Rule fired: mkRule @(_, ()) (T18013a)
Rule fired: Class op fmap (BUILTIN)
Rule fired: mkRule @((), _) (T18013a)
Rule fired: mkRule @(_, ()) (T18013a)
Rule fired: Class op fmap (BUILTIN)
==================== Tidy Core ====================
......
......@@ -4,7 +4,7 @@ Result size of Tidy Core
= {terms: 106, types: 47, coercions: 0, joins: 0/0}
-- RHS size: {terms: 6, types: 3, coercions: 0, joins: 0/0}
T7360.$WFoo3 [InlPrag=INLINE[0]] :: Int -> Foo
T7360.$WFoo3 [InlPrag=INLINE[0] CONLIKE] :: Int -> Foo
[GblId[DataConWrapper],
Arity=1,
Caf=NoCafRefs,
......
module Main (main) where
{- This program is designed to check that case-of-known-constructor
fires even if an application of a DataCon wrapper is floated out:
* The early FloatOut pass will float `D False` out of `g`, since
it’s a constant, non-trivial expression.
* But since `D` is strict, the floated-out expression will actually
be `$WD False`.
* In simplifier phase 2, `f` will be inlined into `g`, leading to a
case expression that scrutinizes the floated-out binding.
* If case-of-known-constructor fires, we’ll end up with `notRule
False`, the RULE will fire, and we get True.
* If it doesn’t fire at phase 2, it will fire later at phase 0 when
we inline the DataCon wrapper. But now the RULE is inactive, so
we’ll end up with False instead.
We want case-of-known-constructor to fire early, so we want the output
to be True. See #18012 for more details. -}
main :: IO ()
main = print (g ())
data T = D !Bool
notRule :: Bool -> Bool
notRule x = x
{-# INLINE [0] notRule #-}
{-# RULES "notRule/False" [~0] notRule False = True #-}
f :: T -> () -> Bool
f (D a) () = notRule a
{-# INLINE [100] f #-} -- so it isn’t inlined before FloatOut
g :: () -> Bool
g x = f (D False) x
{-# NOINLINE g #-}
......@@ -93,3 +93,4 @@ test('T15840a', normal, compile_and_run, [''])
test('T16066', exit_code(1), compile_and_run, ['-O1'])
test('T17206', exit_code(1), compile_and_run, [''])
test('T17151', [], multimod_compile_and_run, ['T17151', ''])
test('T18012', normal, compile_and_run, [''])
T16029.$WMkT [InlPrag=INLINE[0]] :: Int -> Int -> T
T16029.$WMkT [InlPrag=INLINE[0] CONLIKE] :: Int -> Int -> T
Tmpl= \ (dt [Occ=Once!] :: Int) (dt [Occ=Once!] :: Int) ->
= \ (dt [Occ=Once!] :: Int) (dt [Occ=Once!] :: Int) ->
:: GHC.Prim.Int# -> GHC.Prim.Int#
......
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