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Following #22924 this patch narrows the test that stops
us decomposing newtypes. The key change is the use of
noGivenNewtypeReprEqs in GHC.Tc.Solver.Canonical.canTyConApp.
We went to and fro on the solution, as you can see in #22924.
The result is carefully documented in
Note [Decomoposing newtype equalities]
On the way I had revert most of
commit 3e827c3f74ef76d90d79ab6c4e71aa954a1a6b90
Author: Richard Eisenberg <rae@cs.brynmawr.edu>
Date: Mon Dec 5 10:14:02 2022 -0500
Do newtype unwrapping in the canonicaliser and rewriter
See Note [Unwrap newtypes first], which has the details.
It turns out that
(a) 3e827c3f makes GHC behave worse on some recursive newtypes
(see one of the tests on this commit)
(b) the finer-grained test (namely noGivenNewtypeReprEqs) renders
3e827c3f unnecessary
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See Note [Unwrap newtypes first], which has the details.
Close #22519.
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This implements proposal 547 and closes ticket #22298.
See the proposal and ticket for motivation.
Compiler perf improves a bit
Metrics: compile_time/bytes allocated
-------------------------------------
CoOpt_Singletons(normal) -2.4% GOOD
T12545(normal) +1.0%
T13035(normal) -13.5% GOOD
T18478(normal) +0.9%
T9872d(normal) -2.2% GOOD
geo. mean -0.2%
minimum -13.5%
maximum +1.0%
Metric Decrease:
CoOpt_Singletons
T13035
T9872d
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This big patch addresses the rats-nest of issues that have plagued
us for years, about the relationship between Type and Constraint.
See #11715/#21623.
The main payload of the patch is:
* To introduce CONSTRAINT :: RuntimeRep -> Type
* To make TYPE and CONSTRAINT distinct throughout the compiler
Two overview Notes in GHC.Builtin.Types.Prim
* Note [TYPE and CONSTRAINT]
* Note [Type and Constraint are not apart]
This is the main complication.
The specifics
* New primitive types (GHC.Builtin.Types.Prim)
- CONSTRAINT
- ctArrowTyCon (=>)
- tcArrowTyCon (-=>)
- ccArrowTyCon (==>)
- funTyCon FUN -- Not new
See Note [Function type constructors and FunTy]
and Note [TYPE and CONSTRAINT]
* GHC.Builtin.Types:
- New type Constraint = CONSTRAINT LiftedRep
- I also stopped nonEmptyTyCon being built-in; it only needs to be wired-in
* Exploit the fact that Type and Constraint are distinct throughout GHC
- Get rid of tcView in favour of coreView.
- Many tcXX functions become XX functions.
e.g. tcGetCastedTyVar --> getCastedTyVar
* Kill off Note [ForAllTy and typechecker equality], in (old)
GHC.Tc.Solver.Canonical. It said that typechecker-equality should ignore
the specified/inferred distinction when comparein two ForAllTys. But
that wsa only weakly supported and (worse) implies that we need a separate
typechecker equality, different from core equality. No no no.
* GHC.Core.TyCon: kill off FunTyCon in data TyCon. There was no need for it,
and anyway now we have four of them!
* GHC.Core.TyCo.Rep: add two FunTyFlags to FunCo
See Note [FunCo] in that module.
* GHC.Core.Type. Lots and lots of changes driven by adding CONSTRAINT.
The key new function is sORTKind_maybe; most other changes are built
on top of that.
See also `funTyConAppTy_maybe` and `tyConAppFun_maybe`.
* Fix a longstanding bug in GHC.Core.Type.typeKind, and Core Lint, in
kinding ForAllTys. See new tules (FORALL1) and (FORALL2) in GHC.Core.Type.
(The bug was that before (forall (cv::t1 ~# t2). blah), where
blah::TYPE IntRep, would get kind (TYPE IntRep), but it should be
(TYPE LiftedRep). See Note [Kinding rules for types] in GHC.Core.Type.
* GHC.Core.TyCo.Compare is a new module in which we do eqType and cmpType.
Of course, no tcEqType any more.
* GHC.Core.TyCo.FVs. I moved some free-var-like function into this module:
tyConsOfType, visVarsOfType, and occCheckExpand. Refactoring only.
* GHC.Builtin.Types. Compiletely re-engineer boxingDataCon_maybe to
have one for each /RuntimeRep/, rather than one for each /Type/.
This dramatically widens the range of types we can auto-box.
See Note [Boxing constructors] in GHC.Builtin.Types
The boxing types themselves are declared in library ghc-prim:GHC.Types.
GHC.Core.Make. Re-engineer the treatment of "big" tuples (mkBigCoreVarTup
etc) GHC.Core.Make, so that it auto-boxes unboxed values and (crucially)
types of kind Constraint. That allows the desugaring for arrows to work;
it gathers up free variables (including dictionaries) into tuples.
See Note [Big tuples] in GHC.Core.Make.
There is still work to do here: #22336. But things are better than
before.
* GHC.Core.Make. We need two absent-error Ids, aBSENT_ERROR_ID for types of
kind Type, and aBSENT_CONSTRAINT_ERROR_ID for vaues of kind Constraint.
Ditto noInlineId vs noInlieConstraintId in GHC.Types.Id.Make;
see Note [inlineId magic].
* GHC.Core.TyCo.Rep. Completely refactor the NthCo coercion. It is now called
SelCo, and its fields are much more descriptive than the single Int we used to
have. A great improvement. See Note [SelCo] in GHC.Core.TyCo.Rep.
* GHC.Core.RoughMap.roughMatchTyConName. Collapse TYPE and CONSTRAINT to
a single TyCon, so that the rough-map does not distinguish them.
* GHC.Core.DataCon
- Mainly just improve documentation
* Some significant renamings:
GHC.Core.Multiplicity: Many --> ManyTy (easier to grep for)
One --> OneTy
GHC.Core.TyCo.Rep TyCoBinder --> GHC.Core.Var.PiTyBinder
GHC.Core.Var TyCoVarBinder --> ForAllTyBinder
AnonArgFlag --> FunTyFlag
ArgFlag --> ForAllTyFlag
GHC.Core.TyCon TyConTyCoBinder --> TyConPiTyBinder
Many functions are renamed in consequence
e.g. isinvisibleArgFlag becomes isInvisibleForAllTyFlag, etc
* I refactored FunTyFlag (was AnonArgFlag) into a simple, flat data type
data FunTyFlag
= FTF_T_T -- (->) Type -> Type
| FTF_T_C -- (-=>) Type -> Constraint
| FTF_C_T -- (=>) Constraint -> Type
| FTF_C_C -- (==>) Constraint -> Constraint
* GHC.Tc.Errors.Ppr. Some significant refactoring in the TypeEqMisMatch case
of pprMismatchMsg.
* I made the tyConUnique field of TyCon strict, because I
saw code with lots of silly eval's. That revealed that
GHC.Settings.Constants.mAX_SUM_SIZE can only be 63, because
we pack the sum tag into a 6-bit field. (Lurking bug squashed.)
Fixes
* #21530
Updates haddock submodule slightly.
Performance changes
~~~~~~~~~~~~~~~~~~~
I was worried that compile times would get worse, but after
some careful profiling we are down to a geometric mean 0.1%
increase in allocation (in perf/compiler). That seems fine.
There is a big runtime improvement in T10359
Metric Decrease:
LargeRecord
MultiLayerModulesTH_OneShot
T13386
T13719
Metric Increase:
T8095
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Also add perf test for infinite list fusion.
In particular, in `GHC.Core`, often we deal with infinite lists of roles. Also in a few locations we deal with infinite lists of names.
Thanks to simonpj for helping to write the Note [Fusion for `Infinite` lists].
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Co-authored by: Sam Derbyshire
Previously, GHC had three flavours of constraint:
Wanted, Given, and Derived. This removes Derived constraints.
Though serving a number of purposes, the most important role
of Derived constraints was to enable better error messages.
This job has been taken over by the new RewriterSets, as explained
in Note [Wanteds rewrite wanteds] in GHC.Tc.Types.Constraint.
Other knock-on effects:
- Various new Notes as I learned about under-described bits of GHC
- A reshuffling around the AST for implicit-parameter bindings,
with better integration with TTG.
- Various improvements around fundeps. These were caused by the
fact that, previously, fundep constraints were all Derived,
and Derived constraints would get dropped. Thus, an unsolved
Derived didn't stop compilation. Without Derived, this is no
longer possible, and so we have to be considerably more careful
around fundeps.
- A nice little refactoring in GHC.Tc.Errors to center the work
on a new datatype called ErrorItem. Constraints are converted
into ErrorItems at the start of processing, and this allows for
a little preprocessing before the main classification.
- This commit also cleans up the behavior in generalisation around
functional dependencies. Now, if a variable is determined by
functional dependencies, it will not be quantified. This change
is user facing, but it should trim down GHC's strange behavior
around fundeps.
- Previously, reportWanteds did quite a bit of work, even on an empty
WantedConstraints. This commit adds a fast path.
- Now, GHC will unconditionally re-simplify constraints during
quantification. See Note [Unconditionally resimplify constraints when
quantifying], in GHC.Tc.Solver.
Close #18398.
Close #18406.
Solve the fundep-related non-confluence in #18851.
Close #19131.
Close #19137.
Close #20922.
Close #20668.
Close #19665.
-------------------------
Metric Decrease:
LargeRecord
T9872b
T9872b_defer
T9872d
TcPlugin_RewritePerf
-------------------------
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Fixes #21011
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See Note [Equality on FunTys] in TyCoRep.
Close #17675.
Close #17655, about documentation improvements included in
this patch.
Close #19677, about a further mistake around FunTy.
test cases: typecheck/should_compile/T19677
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Type-checking plugins can now directly rewrite type-families.
The TcPlugin record is given a new field, tcPluginRewrite.
The plugin specifies how to rewrite certain type-families with a value
of type `UniqFM TyCon TcPluginRewriter`, where:
type TcPluginRewriter
= RewriteEnv -- Rewriter environment
-> [Ct] -- Givens
-> [TcType] -- type family arguments
-> TcPluginM TcPluginRewriteResult
data TcPluginRewriteResult
= TcPluginNoRewrite
| TcPluginRewriteTo
{ tcPluginRewriteTo :: Reduction
, tcRewriterNewWanteds :: [Ct]
}
When rewriting an exactly-saturated type-family application,
GHC will first query type-checking plugins for possible rewritings
before proceeding.
Includes some changes to the TcPlugin API, e.g. removal
of the EvBindsVar parameter to the TcPluginM monad.
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We define Reduction = Reduction Coercion !Type.
A reduction of the form 'Reduction co new_ty' witnesses an
equality ty ~co~> new_ty.
That is, the rewriting happens left-to-right: the right-hand-side
type of the coercion is the rewritten type, and the left-hand-side
type the original type.
Sticking to this convention makes the codebase more consistent,
helping to avoid certain applications of SymCo.
This replaces the parts of the codebase which represented reductions as
pairs, (Coercion,Type) or (Type,Coercion).
Reduction being strict in the Type argument improves performance
in some programs that rewrite many type families (such as T9872).
Fixes #20161
-------------------------
Metric Decrease:
T5321Fun
T9872a
T9872b
T9872c
T9872d
-------------------------
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This creates new modules GHC.Tc.Solver.InertSet and
GHC.Tc.Solver.Types. The Monad module is still pretty
big, but this is an improvement. Moreover, it means
that GHC.HsToCore.Pmc.Solver.Types no longer depends
on the constraint solver (it now depends on GHC.Tc.Solver.InertSet),
making the error-messages work easier.
This patch thus contributes to #18516.
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Replace uses of WARN macro with calls to:
warnPprTrace :: Bool -> SDoc -> a -> a
Remove the now unused HsVersions.h
Bump haddock submodule
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There is no reason to use CPP. __LINE__ and __FILE__ macros are now
better replaced with GHC's CallStack. As a bonus, assert error messages
now contain more information (function name, column).
Here is the mapping table (HasCallStack omitted):
* ASSERT: assert :: Bool -> a -> a
* MASSERT: massert :: Bool -> m ()
* ASSERTM: assertM :: m Bool -> m ()
* ASSERT2: assertPpr :: Bool -> SDoc -> a -> a
* MASSERT2: massertPpr :: Bool -> SDoc -> m ()
* ASSERTM2: assertPprM :: m Bool -> SDoc -> m ()
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No changes to code; no changes to theory. Just better
explanation.
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As noted in #19102, we would previously ended up reboxing the tuple
result of `split`'s worker and then immediately take apart the boxed
tuple to again unpack it into an unboxed result.
Fixes #19102.
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Following the example of Note [The one-shot state monad trick].
c.f. #18202.
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See Note [Error on unconstrained meta-variables] in TcMType.
Close #17301
Close #17567
Close #17562
Close #15474
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Provoked by #18987, this patch adds a missing zonkQuickLook of
app_res_rho in tcApp.
Most of the time this zonk is unnecesary. In fact, I can't think of a
concrete case where it is needed -- hence no test. But even if it
isn't necessary, the reasoning that allows it to be omitted is very
subtle. So I've put it in.
However, adding this zonk does /not/ affect the emitted constraints,
so the reported symptoms for #18987 remain, but harmlessly so, and now
documented in a new Note [Instantiation variables are short lived]
in GHC.Tc.Gen.App.
No change in behaviour, no tests.
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Now that flattening doesn't produce flattening variables,
it's not really flattening anything: it's rewriting. This
change also means that the rewriter can no longer be confused
the core flattener (in GHC.Core.Unify), which is sometimes used
during type-checking.
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