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1b4a622f
by sheaf at 2026-09-17T02:39:13-04:00
Improvements to type/data family handling
This commit makes several improvements to the treatment of type and data
families in GHC:
- We consistently use "type family" instead of "type synonym family"
to avoid a confusion with type synonyms. For example:
- OpenSynFamilyTyCon ==> OpenTypeFamilyTyCon
- ClosedSynFamilyTyCon => ClosedTypeFamilyTyCon
- Various functions that were specific to data families have been
renamed to make this clear. For example:
- tyConFamInst_maybe ==> tyConDataFamInst_maybe
- isFamInstTyCon ==> isDataFamInstTyCon
- 'FamTyConFlav' has been refactored so that all closed type families
share a single 'ClosedTypeFamilyTyCon' constructor.
The corresponding 'IfaceFamTyConFlav' type was updated similarly.
This is then used to tidy up the implementation of
GHC.Core.FamInstEnv.reduceTyFamApp_maybe.
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c5aa9098
by sheaf at 2026-09-17T02:39:13-04:00
Small refactor of lookupFamInstEnv
This commit reworks the code for looking up family instances in
GHC.Core.FamInstEnv, reducing duplication a little bit.
No change in behaviour.
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a3ad4588
by sheaf at 2026-09-17T02:39:14-04:00
Use a type family for boxing unboxed types
This commit overhauls the way in which unboxed types are boxed, as per
the updated Note [Boxing constructors] in GHC.Builtin.WiredIn.Types.Box.
The main change is to allow boxing to be parametrised by representation,
e.g. making 'Box ty' a valid type. We achieve this by implementing 'Box'
using a closed type family:
newtype Box (a :: TYPE r) = Box (BoxTF r)
type BoxTF :: RuntimeRep -> Type
type family BoxTF r where
BoxTF IntRep = BoxInt
BoxTF Int8Rep = BoxInt8
BoxTF WordRep = BoxWord
BoxTF LiftedRep = Any @Type
BoxTF (TupleRep [r1, r2]) = (BoxTF r1, BoxTF r2)
...
BoxTF (SumRep rs) = BoxSum rs
This new design solves the following problems:
- It allows boxing a type whose 'RuntimeRep' has not yet been
determined (e.g. because we only learn the 'RuntimeRep' after
constraint solving). That is, 'Box @r a' is a perfectly valid type
even if 'r' is an unfilled metavariable. This is a requirement
to fix #25065 (in which we need to box a type whose 'RuntimeRep'
is only filled in during constraint solving).
- It handles boxing of unboxed tuples and unboxed sums, via recursive
boxing. See Note [Boxing TupleRep and SumRep] in
GHC.Builtin.WiredIn.Types.Box.
'Box', 'BoxTF' and all of the boxing data constructors are defined in
a new 'ghc-internal' module, 'GHC.Internal.Box'. This module contains
nothing but wired-in declarations, and GHC never loads its interface on
account of a wired-in thing (GHC.Builtin.Modules.isWiredInOnlyModule);
see Note [Loading instances for wired-in things] in GHC.Iface.Load.
The individual boxing data constructors are deliberately left as an
internal implementation detail, and not exported. The intended API is
via the two new magic 'Id's:
box :: forall {r} (a :: TYPE r). a -> Box a
unbox :: forall {r} (a :: TYPE r). Box a -> a
exported from 'GHC.PrimOps' (in 'ghc-experimental'). The old boxing
data types (IntBox, WordBox, FloatBox, DoubleBox, DictBox) are no longer
exported from base (CLC proposal #421).
We use this new design to consistently desugar:
- parallel comprehensions (GHC.HsToCore.ListComp.{deListComp,dsMcStmt})
- then/group/using statements (GHC.HsToCore.ListComp.{dsTransStmt,dsMcStmt})
- recursive do blocks (mdo/rec) (GHC.HsToCore.Expr.dsDo)
- arrows (GHC.HsToCore.Arrows)
by consistently using 'box'/'unbox' to deal with unboxed types being put
into big tuples. We also adapt 'GHC.Tc.Gen.Match.{tcMcStmt,tcDoStmt}'
to create fresh /representation-polymorphic/ type variables for the
binders that we are going to put into a big tuple (previously, GHC only
allowed lifted types in that position).
These desugaring of box and unbox is explained in
Note [Desugaring box & unbox] in GHC.Core.Make.Box. Roughly speaking,
the desugaring looks like:
box @r @ty e ==> K e
unbox @r @ty e ==> case e of K x -> x
where 'K' is the boxing data constructor at RuntimeRep 'r'. It's
slightly more complicated than that in practice: we first need to
insert a cast (see Note [The canonical type of a RuntimeRep]) using the
new 'CanonicalProv' 'UnivCoProvenance', and unboxed tuples/sums need
recursive logic explained in Note [box/unbox for unboxed tuples and sums],
including a specific 'BoxSum' datatypes for unboxed sum (which also
needed a wired-in type-level list indexing type family (!!)).
The desugaring happens in two ways:
- Occurrences of 'box'/'unbox' emitted by the typechecker are
eliminated in the 'ds_app_var' case of GHC.HsToCore.Expr.
- Other code that needs to box/unbox emits the appropriate code inline.
This includes the big tuple machinery of GHC.Core.Make used by the
desugarer (GHC.HsToCore.{Utils,Binds,Arrows,ListComp}) as well as
the float-out pass (GHC.Core.Opt.SetLevels).
Core Lint checks that no occurrence of 'box'/'unbox' survives desugaring.
On the way, we overhaul the litany of big tuple functions by introducing
data BigTupleLayout = BoxedElements | BareElements
to distinguish the two kinds of "big tuples" that GHC routinely deals
with; for example 'mkBigCoreVarTupSolo' becomes 'mkBigCoreVarTup BareElements'.
All of this code is moved to the new module GHC.Core.Make.BigTuple.
Fixes #20864 #22336 #22473 #25065 #27331
-------------------------
Metric Decrease:
T9872a
-------------------------
-
4cf7628a
by Evgeny Malyshev at 2026-09-17T02:39:56-04:00
Fix the CompactionFailed documentation link to compact
The old Haddock reference links into base instead of ghc-compact.
Use an explicit URL because ghc-compact depends on base, not vice versa.
Fixes #27558
Assisted-By: OpenAI Codex
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098bba70
by Facundo Domínguez at 2026-09-17T14:57:41-04:00
Remove the call to hoistFlag from processCmdLineP
This call was undesirable because it was causing a reconstruction
of the list of flag processors.
Even relying on list fusion would not be sufficient because we want
to replace the list with a data structure with faster lookups to
address #25763.
The removal is done in two moves:
* We move CmdLineP to CmdLine.hs
* Then we move the effect of hoisting to processArgs via a new function
hoistEwM
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e01799c7
by Facundo Domínguez at 2026-09-17T14:57:42-04:00
Do not create duplicate flag processors for the -W flag
This makes simpler implementing the command line parser with a trie map
holding flag processors. If we were to allow duplicate flag processors
for any flag, the trie map would need to be a multimap.
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3875b257
by Facundo Domínguez at 2026-09-17T14:57:42-04:00
Replace the list of flag processors with a trie map in `processArgs`
Previously `GHC.Driver.CmdLine.findArg` was called for each
command-line argument, doing a linear search on the list of flag
processors each time. This was somewhat costly as the list of flag
processor has near 2000 elements.
A lookup with a trie map is faster in general, but the speed up is
only noticeable when calling `GHC.Driver.CmdLine.processArgs` sufficient
times, so the amount of lookups piles up. This could happen in large
projects with many units each having many dependencies. If only a
module needs to be recompiled, the user still needs to wait for all of
the flag parsing to complete.
The benchmark at testsuite/tests/perf/compiler/cmdline-parser shows a
10x speed up when using the trie.
The trie map is implemented in `GHC.Data.StringTrie`.
The design is explained in Note [Processing command line argument fast]
in GHC.Driver.Session.
The commit also:
* adds two property-based tests for trie map operations,
* adds a benchmark of the command line parser, and
* renames the predicate `arg_ok` to `valid_flag_suffix` to decide what
flag processor should be used when there are multiple matching
prefixes on a flag.
Fixes #25763.
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5236634a
by Andreas Klebinger at 2026-09-17T14:58:24-04:00
Compile Word64{Map,Set} with -O2 always.
This is the hottest code and even if we build GHC with -O0 otherwise -O2
pays off for these modules.
Fixes #27814.
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ede4f3c8
by Duncan Coutts at 2026-09-21T12:33:18+01:00
Fix a couple comments in the new selectbis I/O manager
Noticed late in the review process.
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bae3bb2b
by Duncan Coutts at 2026-09-21T12:33:18+01:00
New rts_IOManagerFeatures bitset for I/O manager features
The idea is that code in the RTS and ghc-internal can use this feature
bitset to do things that have to be conditional. But instead of basing
it on threaded/non-threaded, win32 etc it can be based on features of
the current I/O manager.
In particular this will allow us to have in-RTS I/O managers when using
the threaded RTS way, by changing code to use the feature test rather
than testing for threaded/non-threaded.
There are also numerous conditions in existing RTS and library code that
could benefit from being clearly based on I/O manager features rather
than on (historically) correlated aspects of the platform.
For example, a major difference between WinIO and the win32-legacy I/O
manager is whether it uses C lib fds or Win32 API HANDLEs. This
distinction is not necessarily unique forever to these I/O managers.
Future Windows I/O managers may want to take advantage of the same
distinction.
For example, we could have a feature to say if the I/O manager supports
readiness notifications threadWaitRead# etc (win32-legacy does not
support these for example), so I/O code in ghc-internal can use
appropriate workarounds.
Similarly, if/when we add support for async I/O, or I/O to files at
given offsets (without affecting or being affected by the file pointer)
then library code can consult the feature bits and either use emulated
fallbacks or throw appropriate exceptions.
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96ad1aa4
by Duncan Coutts at 2026-09-21T12:33:18+01:00
Use rts_IOManagerFeatures bitset in GHC.Internal.IO.SubSystem
Establish a pattern for exposing the features. We will start using them
in subsequent commits.
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885549aa
by Duncan Coutts at 2026-09-21T12:33:18+01:00
Turn rts_IOManagerIsWin32Native into a feature bit of rts_IOManagerFeatures
And update where it is used in ghc-internal