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This patch fixes #22745 and #15205, which are about GHC's
failure to discard unnecessary superclass selections that
yield coercions. See
GHC.Core.Utils Note [exprOkForSpeculation and type classes]
The main changes are:
* Write new Note [NON-BOTTOM_DICTS invariant] in GHC.Core, and
refer to it
* Define new function isTerminatingType, to identify those
guaranteed-terminating dictionary types.
* exprOkForSpeculation has a new (very simple) case for ClassOpId
* ClassOpId has a new field that says if the return type is
an unlifted type, or a terminating type.
This was surprisingly tricky to get right. In particular note
that unlifted types are not terminating types; you can write an
expression of unlifted type, that diverges. Not so for dictionaries
(or, more precisely, for the dictionaries that GHC constructs).
Metric Decrease:
LargeRecord
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This patch massages the keys used in the `TmOracle` `CoreMap` to ensure
that dictionaries of coherent classes give the same key.
That is, whenever we have an expression we want to insert or lookup in
the `TmOracle` `CoreMap`, we first replace any dictionary
`$dict_abcd :: ct` with a value of the form `error @ct`.
This allows us to common-up view pattern functions with required
constraints whose arguments differed only in the uniques of the
dictionaries they were provided, thus fixing #21662.
This is a rather ad-hoc change to the keys used in the
`TmOracle` `CoreMap`. In the long run, we would probably want to use
a different representation for the keys instead of simply using
`CoreExpr` as-is. This more ambitious plan is outlined in #19272.
Fixes #21662
Updates unix submodule
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This patch addresses #21831, point 2. See
Note [generaliseDictPats] in SpecConstr
I took the opportunity to refactor the construction of specialisation
rules a bit, so that the rule name says what type we are specialising
at.
Surprisingly, there's a 20% decrease in compile time for test
perf/compiler/T18223. I took a look at it, and the code size seems the
same throughout. I did a quick ticky profile which seemed to show a
bit less substitution going on. Hmm. Maybe it's the "don't do
eta-expansion in stable unfoldings" patch, which is part of the
same MR as this patch.
Anyway, since it's a move in the right direction, I didn't think it
was worth looking into further.
Metric Decrease:
T18223
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This patch fixes the unification of concrete type variables.
The subtlety was that unifying concrete metavariables is more subtle
than other metavariables, as decomposition is possible. See the Note
[Unifying concrete metavariables], which explains how we unify a
concrete type variable with a type 'ty' by concretising 'ty', using
the function 'GHC.Tc.Utils.Concrete.concretise'.
This can be used to perform an eager syntactic check for concreteness,
allowing us to remove the IsRefl# special predicate. Instead of emitting
two constraints `rr ~# concrete_tv` and `IsRefl# rr concrete_tv`, we
instead concretise 'rr'. If this succeeds we can fill 'concrete_tv',
and otherwise we directly emit an error message to the typechecker
environment instead of deferring. We still need the error message
to be passed on (instead of directly thrown), as we might benefit from
further unification in which case we will need to zonk the stored types.
To achieve this, we change the 'wc_holes' field of 'WantedConstraints'
to 'wc_errors', which stores general delayed errors. For the moement,
a delayed error is either a hole, or a syntactic equality error.
hasFixedRuntimeRep_MustBeRefl is now hasFixedRuntimeRep_syntactic, and
hasFixedRuntimeRep has been refactored to directly return the most
useful coercion for PHASE 2 of FixedRuntimeRep.
This patch also adds a field ir_frr to the InferResult datatype,
holding a value of type Maybe FRROrigin. When this value is not
Nothing, this means that we must fill the ir_ref field with a type
which has a fixed RuntimeRep.
When it comes time to fill such an ExpType, we ensure that the type
has a fixed RuntimeRep by performing a representation-polymorphism
check with the given FRROrigin
This is similar to what we already do to ensure we fill an Infer
ExpType with a type of the correct TcLevel.
This allows us to properly perform representation-polymorphism checks
on 'Infer' 'ExpTypes'.
The fillInferResult function had to be moved to GHC.Tc.Utils.Unify
to avoid a cyclic import now that it calls hasFixedRuntimeRep.
This patch also changes the code in matchExpectedFunTys to make use
of the coercions, which is now possible thanks to the previous change.
This implements PHASE 2 of FixedRuntimeRep in some situations.
For example, the test cases T13105 and T17536b are now both accepted.
Fixes #21239 and #21325
-------------------------
Metric Decrease:
T18223
T5631
-------------------------
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This patch introduces a new kind of metavariable, by adding the
constructor `ConcreteTv` to `MetaInfo`. A metavariable with
`ConcreteTv` `MetaInfo`, henceforth a concrete metavariable, can only
be unified with a type that is concrete (that is, a type that answers
`True` to `GHC.Core.Type.isConcrete`).
This solves the problem of dangling metavariables in `Concrete#`
constraints: instead of emitting `Concrete# ty`, which contains a
secret existential metavariable, we simply emit a primitive equality
constraint `ty ~# concrete_tv` where `concrete_tv` is a fresh concrete
metavariable.
This means we can avoid all the complexity of canonicalising
`Concrete#` constraints, as we can just re-use the existing machinery
for `~#`.
To finish things up, this patch then removes the `Concrete#` special
predicate, and instead introduces the special predicate `IsRefl#`
which enforces that a coercion is reflexive.
Such a constraint is needed because the canonicaliser is quite happy
to rewrite an equality constraint such as `ty ~# concrete_tv`, but
such a rewriting is not handled by the rest of the compiler currently,
as we need to make use of the resulting coercion, as outlined in the
FixedRuntimeRep plan.
The big upside of this approach (on top of simplifying the code)
is that we can now selectively implement PHASE 2 of FixedRuntimeRep,
by changing individual calls of `hasFixedRuntimeRep_MustBeRefl` to
`hasFixedRuntimeRep` and making use of the obtained coercion.
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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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PHASE 1: we never rewrite Concrete# evidence.
This patch migrates all the representation polymorphism checks to
the typechecker, using a new constraint form
Concrete# :: forall k. k -> TupleRep '[]
Whenever a type `ty` must be representation-polymorphic
(e.g. it is the type of an argument to a function), we emit a new
`Concrete# ty` Wanted constraint. If this constraint goes
unsolved, we report a representation-polymorphism error to the user.
The 'FRROrigin' datatype keeps track of the context of the
representation-polymorphism check, for more informative error messages.
This paves the way for further improvements, such as
allowing type families in RuntimeReps and improving the soundness
of typed Template Haskell. This is left as future work (PHASE 2).
fixes #17907 #20277 #20330 #20423 #20426
updates haddock submodule
-------------------------
Metric Decrease:
T5642
-------------------------
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This patch fixes #20103, by treating HasCallStack constraints as
cheap when eta-expanding.
See Note [Eta expanding through CallStacks] in GHC.Core.Opt.Arity
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There is a zoo of `splitForAll-` functions in `GHC.Core.Type` (as well as
`tcSplitForAll-` functions in `GHC.Tc.Utils.TcType`) that all do very similar
things, but vary in the particular form of type variable that they return. To
make things worse, the names of these functions are often quite misleading.
Some particularly egregious examples:
* `splitForAllTys` returns `TyCoVar`s, but `splitSomeForAllTys` returns
`VarBndr`s.
* `splitSomeForAllTys` returns `VarBndr`s, but `tcSplitSomeForAllTys` returns
`TyVar`s.
* `splitForAllTys` returns `TyCoVar`s, but `splitForAllTysInvis` returns
`InvisTVBinder`s. (This in particular arose in the context of #18939, and
this finally motivated me to bite the bullet and improve the status quo
vis-à-vis how we name these functions.)
In an attempt to bring some sanity to how these functions are named, I have
opted to rename most of these functions en masse to use consistent suffixes
that describe the particular form of type variable that each function returns.
In concrete terms, this amounts to:
* Functions that return a `TyVar` now use the suffix `-TyVar`.
This caused the following functions to be renamed:
* `splitTyVarForAllTys` -> `splitForAllTyVars`
* `splitForAllTy_ty_maybe` -> `splitForAllTyVar_maybe`
* `tcSplitForAllTys` -> `tcSplitForAllTyVars`
* `tcSplitSomeForAllTys` -> `tcSplitSomeForAllTyVars`
* Functions that return a `CoVar` now use the suffix `-CoVar`.
This caused the following functions to be renamed:
* `splitForAllTy_co_maybe` -> `splitForAllCoVar_maybe`
* Functions that return a `TyCoVar` now use the suffix `-TyCoVar`.
This caused the following functions to be renamed:
* `splitForAllTy` -> `splitForAllTyCoVar`
* `splitForAllTys` -> `splitForAllTyCoVars`
* `splitForAllTys'` -> `splitForAllTyCoVars'`
* `splitForAllTy_maybe` -> `splitForAllTyCoVar_maybe`
* Functions that return a `VarBndr` now use the suffix corresponding to the
most relevant type synonym. This caused the following functions to be renamed:
* `splitForAllVarBndrs` -> `splitForAllTyCoVarBinders`
* `splitForAllTysInvis` -> `splitForAllInvisTVBinders`
* `splitForAllTysReq` -> `splitForAllReqTVBinders`
* `splitSomeForAllTys` -> `splitSomeForAllTyCoVarBndrs`
* `tcSplitForAllVarBndrs` -> `tcSplitForAllTyVarBinders`
* `tcSplitForAllTysInvis` -> `tcSplitForAllInvisTVBinders`
* `tcSplitForAllTysReq` -> `tcSplitForAllReqTVBinders`
* `tcSplitForAllTy_maybe` -> `tcSplitForAllTyVarBinder_maybe`
Note that I left the following functions alone:
* Functions that split apart things besides `ForAllTy`s, such as `splitFunTys`
or `splitPiTys`. Thankfully, there are far fewer of these functions than
there are functions that split apart `ForAllTy`s, so there isn't much of a
pressing need to apply the new naming convention elsewhere.
* Functions that split apart `ForAllCo`s in `Coercion`s, such as
`GHC.Core.Coercion.splitForAllCo_maybe`. We could theoretically apply the new
naming convention here, but then we'd have to figure out how to disambiguate
`Type`-splitting functions from `Coercion`-splitting functions. Ultimately,
the `Coercion`-splitting functions aren't used nearly as much as the
`Type`-splitting functions, so I decided to leave the former alone.
This is purely refactoring and should cause no change in behavior.
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Firstly this improves code clarity.
But it also has performance benefits as we no longer
go through the name of the TyCon to get at it's unique.
In order to make this work the recursion check for TyCon
has been moved into it's own module in order to avoid import
cycles.
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Two bugs, #18627 and #18649, had the same cause: we were not
account for the fact that a constaint tuple might hide an implicit
parameter.
The solution is not hard: look for implicit parameters in
superclasses. See Note [Local implicit parameters] in
GHC.Core.Predicate.
Then we use this new function in two places
* The "short-cut solver" in GHC.Tc.Solver.Interact.shortCutSolver
which simply didn't handle implicit parameters properly at all.
This fixes #18627
* The specialiser, which should not specialise on implicit parameters
This fixes #18649
There are some lingering worries (see Note [Local implicit
parameters]) but things are much better.
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- put panic related functions into GHC.Utils.Panic
- put trace related functions using DynFlags in GHC.Driver.Ppr
One step closer making Outputable fully independent of DynFlags.
Bump haddock submodule
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This is the first step towards implementation of the linear types proposal
(https://github.com/ghc-proposals/ghc-proposals/pull/111).
It features
* A language extension -XLinearTypes
* Syntax for linear functions in the surface language
* Linearity checking in Core Lint, enabled with -dlinear-core-lint
* Core-to-core passes are mostly compatible with linearity
* Fields in a data type can be linear or unrestricted; linear fields
have multiplicity-polymorphic constructors.
If -XLinearTypes is disabled, the GADT syntax defaults to linear fields
The following items are not yet supported:
* a # m -> b syntax (only prefix FUN is supported for now)
* Full multiplicity inference (multiplicities are really only checked)
* Decent linearity error messages
* Linear let, where, and case expressions in the surface language
(each of these currently introduce the unrestricted variant)
* Multiplicity-parametric fields
* Syntax for annotating lambda-bound or let-bound with a multiplicity
* Syntax for non-linear/multiple-field-multiplicity records
* Linear projections for records with a single linear field
* Linear pattern synonyms
* Multiplicity coercions (test LinearPolyType)
A high-level description can be found at
https://ghc.haskell.org/trac/ghc/wiki/LinearTypes/Implementation
Following the link above you will find a description of the changes made to Core.
This commit has been authored by
* Richard Eisenberg
* Krzysztof Gogolewski
* Matthew Pickering
* Arnaud Spiwack
With contributions from:
* Mark Barbone
* Alexander Vershilov
Updates haddock submodule.
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Update Haddock submodule
Metric Increase:
haddock.compiler
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* SysTools
* Parser
* GHC.Builtin
* GHC.Iface.Recomp
* Settings
Update Haddock submodule
Metric Decrease:
Naperian
parsing001
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Update Haddock submodule
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Update Haddock submodule
Metric Increase:
haddock.compiler
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Update submodule: haddock
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