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* Simple subsumptionwip/T17775Simon Peyton Jones2020-06-051-2/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch simplifies GHC to use simple subsumption. Ticket #17775 Implements GHC proposal #287 https://github.com/ghc-proposals/ghc-proposals/blob/master/ proposals/0287-simplify-subsumption.rst All the motivation is described there; I will not repeat it here. The implementation payload: * tcSubType and friends become noticably simpler, because it no longer uses eta-expansion when checking subsumption. * No deeplyInstantiate or deeplySkolemise That in turn means that some tests fail, by design; they can all be fixed by eta expansion. There is a list of such changes below. Implementing the patch led me into a variety of sticky corners, so the patch includes several othe changes, some quite significant: * I made String wired-in, so that "foo" :: String rather than "foo" :: [Char] This improves error messages, and fixes #15679 * The pattern match checker relies on knowing about in-scope equality constraints, andd adds them to the desugarer's environment using addTyCsDs. But the co_fn in a FunBind was missed, and for some reason simple-subsumption ends up with dictionaries there. So I added a call to addTyCsDs. This is really part of #18049. * I moved the ic_telescope field out of Implication and into ForAllSkol instead. This is a nice win; just expresses the code much better. * There was a bug in GHC.Tc.TyCl.Instance.tcDataFamInstHeader. We called checkDataKindSig inside tc_kind_sig, /before/ solveEqualities and zonking. Obviously wrong, easily fixed. * solveLocalEqualitiesX: there was a whole mess in here, around failing fast enough. I discovered a bad latent bug where we could successfully kind-check a type signature, and use it, but have unsolved constraints that could fill in coercion holes in that signature -- aargh. It's all explained in Note [Failure in local type signatures] in GHC.Tc.Solver. Much better now. * I fixed a serious bug in anonymous type holes. IN f :: Int -> (forall a. a -> _) -> Int that "_" should be a unification variable at the /outer/ level; it cannot be instantiated to 'a'. This was plain wrong. New fields mode_lvl and mode_holes in TcTyMode, and auxiliary data type GHC.Tc.Gen.HsType.HoleMode. This fixes #16292, but makes no progress towards the more ambitious #16082 * I got sucked into an enormous refactoring of the reporting of equality errors in GHC.Tc.Errors, especially in mkEqErr1 mkTyVarEqErr misMatchMsg misMatchMsgOrCND In particular, the very tricky mkExpectedActualMsg function is gone. It took me a full day. But the result is far easier to understand. (Still not easy!) This led to various minor improvements in error output, and an enormous number of test-case error wibbles. One particular point: for occurs-check errors I now just say Can't match 'a' against '[a]' rather than using the intimidating language of "occurs check". * Pretty-printing AbsBinds Tests review * Eta expansions T11305: one eta expansion T12082: one eta expansion (undefined) T13585a: one eta expansion T3102: one eta expansion T3692: two eta expansions (tricky) T2239: two eta expansions T16473: one eta determ004: two eta expansions (undefined) annfail06: two eta (undefined) T17923: four eta expansions (a strange program indeed!) tcrun035: one eta expansion * Ambiguity check at higher rank. Now that we have simple subsumption, a type like f :: (forall a. Eq a => Int) -> Int is no longer ambiguous, because we could write g :: (forall a. Eq a => Int) -> Int g = f and it'd typecheck just fine. But f's type is a bit suspicious, and we might want to consider making the ambiguity check do a check on each sub-term. Meanwhile, these tests are accepted, whereas they were previously rejected as ambiguous: T7220a T15438 T10503 T9222 * Some more interesting error message wibbles T13381: Fine: one error (Int ~ Exp Int) rather than two (Int ~ Exp Int, Exp Int ~ Int) T9834: Small change in error (improvement) T10619: Improved T2414: Small change, due to order of unification, fine T2534: A very simple case in which a change of unification order means we get tow unsolved constraints instead of one tc211: bizarre impredicative tests; just accept this for now Updates Cabal and haddock submodules. Metric Increase: T12150 T12234 T5837 haddock.base Metric Decrease: haddock.compiler haddock.Cabal haddock.base Merge note: This appears to break the `UnliftedNewtypesDifficultUnification` test. It has been marked as broken in the interest of merging. (cherry picked from commit 66b7b195cb3dce93ed5078b80bf568efae904cc5)
* Clean up boot vs non-boot disambiguating typesJohn Ericson2020-06-041-1/+1
| | | | | | | | | | | | | | | We often have (ModuleName, Bool) or (Module, Bool) pairs for "extended" module names (without or with a unit id) disambiguating boot and normal modules. We think this is important enough across the compiler that it deserves a new nominal product type. We do this with synnoyms and a functor named with a `Gen` prefix, matching other newly created definitions. It was also requested that we keep custom `IsBoot` / `NotBoot` sum type. So we have it too. This means changing many the many bools to use that instead. Updates `haddock` submodule.
* Build a threaded stage 1 if the bootstrapping GHC supports it.Travis Whitaker2020-05-291-1/+8
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* Move Config module into GHC.SettingsSylvain Henry2020-05-242-2/+2
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* Allow GHCi :script file names in double quotesStefan Holdermans2020-05-211-2/+5
| | | | | | | | | | | | | | This patch updates the user interface of GHCi so that file names passed to the ':script' command can be wrapped in double quotes. For example: :script "foo bar.script" The implementation uses a modified version of 'words' that treats character sequences enclosed in double quotes as single words. Fixes #18027.
* Allow spaces in GHCi :script file namesStefan Holdermans2020-05-211-1/+14
| | | | | | | | | | | | | | This patch updates the user interface of GHCi so that file names passed to the ':script' command may contain spaces escaped with a backslash. For example: :script foo\ bar.script The implementation uses a modified version of 'words' that does not break on escaped spaces. Fixes #18027.
* GHCi: Add link to the user's guide in help messageTakenobu Tani2020-05-131-0/+4
| | | | | | | This commit adds a link to the user's guide in ghci's `:help` message. Newcomers could easily reach to details of ghci.
* Don't use DynFlags in showLinkerState (#17957)Sylvain Henry2020-05-061-1/+4
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* Remove custom ExceptionMonad class (#18075) (updating haddock submodule ↵Artem Pelenitsyn2020-05-043-80/+26
| | | | accordingly)
* Remove PprStyle param of logging actionsSylvain Henry2020-05-011-2/+2
| | | | Use `withPprStyle` instead to apply a specific style to a SDoc.
* Unit: split and rename modulesSylvain Henry2020-04-303-6/+6
| | | | | | | Introduce GHC.Unit.* hierarchy for everything concerning units, packages and modules. Update Haddock submodule
* Refactoring unit management codeSylvain Henry2020-04-302-6/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Over the years the unit management code has been modified a lot to keep up with changes in Cabal (e.g. support for several library components in the same package), to integrate BackPack, etc. I found it very hard to understand as the terminology wasn't consistent, was referring to past concepts, etc. The terminology is now explained as clearly as I could in the Note "About Units" and the code is refactored to reflect it. ------------------- Many names were misleading: UnitId is not an Id but could be a virtual unit (an indefinite one instantiated on the fly), IndefUnitId constructor may contain a definite instantiated unit, etc. * Rename IndefUnitId into InstantiatedUnit * Rename IndefModule into InstantiatedModule * Rename UnitId type into Unit * Rename IndefiniteUnitId constructor into VirtUnit * Rename DefiniteUnitId constructor into RealUnit * Rename packageConfigId into mkUnit * Rename getPackageDetails into unsafeGetUnitInfo * Rename InstalledUnitId into UnitId Remove references to misleading ComponentId: a ComponentId is just an indefinite unit-id to be instantiated. * Rename ComponentId into IndefUnitId * Rename ComponentDetails into UnitPprInfo * Fix display of UnitPprInfo with empty version: this is now used for units dynamically generated by BackPack Generalize several types (Module, Unit, etc.) so that they can be used with different unit identifier types: UnitKey, UnitId, Unit, etc. * GenModule: Module, InstantiatedModule and InstalledModule are now instances of this type * Generalize DefUnitId, IndefUnitId, Unit, InstantiatedUnit, PackageDatabase Replace BackPack fake "hole" UnitId by a proper HoleUnit constructor. Add basic support for UnitKey. They should be used more in the future to avoid mixing them up with UnitId as we do now. Add many comments. Update Haddock submodule
* Refactor UnitInfoSylvain Henry2020-04-301-3/+3
| | | | | | | | | | | | | | | | | | | | | * Rename InstalledPackageInfo into GenericUnitInfo The name InstalledPackageInfo is only kept for alleged backward compatibility reason in Cabal. ghc-boot has its own stripped down copy of this datatype but it doesn't need to keep the name. Internally we already use type aliases (UnitInfo in GHC, PackageCacheFormat in ghc-pkg). * Rename UnitInfo fields: add "unit" prefix and fix misleading names * Add comments on every UnitInfo field * Rename SourcePackageId into PackageId "Package" already indicates that it's a "source package". Installed package components are called units. Update Haddock submodule
* Modules: Utils and Data (#13009)Sylvain Henry2020-04-266-35/+35
| | | | | | | Update Haddock submodule Metric Increase: haddock.compiler
* Fix tab-completion for :break (#17989)Roland Senn2020-04-221-10/+108
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In tab-completion for the `:break` command, only those identifiers should be shown, that are accepted in the `:break` command. Hence these identifiers must be - defined in an interpreted module - top-level - currently in scope - listed in a `ModBreaks` value as a possible breakpoint. The identifiers my be qualified or unqualified. To get all possible top-level breakpoints for tab-completeion with the correct qualification do: 1. Build the list called `pifsBreaks` of all pairs of (Identifier, module-filename) from the `ModBreaks` values. Here all identifiers are unqualified. 2. Build the list called `pifInscope` of all pairs of (Identifiers, module-filename) with identifiers from the `GlobalRdrEnv`. Take only those identifiers that are in scope and have the correct prefix. Here the identifiers may be qualified. 3. From the `pifInscope` list seclect all pairs that can be found in the `pifsBreaks` list, by comparing only the unqualified part of the identifier. The remaining identifiers can be used for tab-completion. This ensures, that we show only identifiers, that can be used in a `:break` command.
* Use ParserFlags in GHC.Runtime.Eval (#17957)Sylvain Henry2020-04-211-4/+4
| | | | | | Instead of passing `DynFlags` to functions such as `isStmt` and `hasImport` in `GHC.Runtime.Eval` we pass `ParserFlags`. It's a much simpler structure that can be created purely with `mkParserFlags'`.
* Modules (#13009)Sylvain Henry2020-04-183-7/+7
| | | | | | | | | | | | | | * SysTools * Parser * GHC.Builtin * GHC.Iface.Recomp * Settings Update Haddock submodule Metric Decrease: Naperian parsing001
* Modules: type-checker (#13009)Sylvain Henry2020-04-073-4/+4
| | | | Update Haddock submodule
* Store ComponentId detailsSylvain Henry2020-03-292-4/+5
| | | | | | | | | | | | | | | | As far as GHC is concerned, installed package components ("units") are identified by an opaque ComponentId string provided by Cabal. But we don't want to display it to users (as it contains a hash) so GHC queries the database to retrieve some infos about the original source package (name, version, component name). This patch caches these infos in the ComponentId itself so that we don't need to provide DynFlags (which contains installed package informations) to print a ComponentId. In the future we want GHC to support several independent package states (e.g. for plugins and for target code), hence we need to avoid implicitly querying a single global package state.
* Modules: Types (#13009)Sylvain Henry2020-03-296-23/+22
| | | | | | | Update Haddock submodule Metric Increase: haddock.compiler
* Modules: Core (#13009)Sylvain Henry2020-03-161-1/+1
| | | | Update submodule: haddock
* Use a Set to represent WaysSylvain Henry2020-03-112-3/+4
| | | | | | | | Should make `member` queries faster and avoid messing up with missing `nubSort`. Metric Increase: hie002
* Refactor GHC.Driver.Session (Ways and Flags)Sylvain Henry2020-03-111-4/+5
| | | | | | | | | | | | | * extract flags and ways into their own modules (with some renaming) * remove one SOURCE import of GHC.Driver.Session from GHC.Driver.Phases * when GHC uses dynamic linking (WayDyn), `interpWays` was only reporting WayDyn even if the host was profiled (WayProf). Now it returns both as expected (might fix #16803). * `mkBuildTag :: [Way] -> String` wasn't reporting a canonical tag for differently ordered lists. Now we sort and nub the list to fix this.
* Refactor runtime interpreter codeSylvain Henry2020-02-291-7/+9
| | | | | | | | | | | | | | | In #14335 we want to be able to use both the internal interpreter (for the plugins) and the external interpreter (for TH and GHCi) at the same time. This patch performs some preliminary refactoring: the `hsc_interp` field of HscEnv replaces `hsc_iserv` and is now used to indicate which interpreter (internal, external) to use to execute TH and GHCi. Opt_ExternalInterpreter flag and iserv options in DynFlags are now queried only when we set the session DynFlags. It should help making GHC multi-target in the future by selecting an interpreter according to the selected target.
* Monotonic locations (#17632)Vladislav Zavialov2020-02-293-15/+15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | When GHC is parsing a file generated by a tool, e.g. by the C preprocessor, the tool may insert #line pragmas to adjust the locations reported to the user. As the result, the locations recorded in RealSrcLoc are not monotonic. Elements that appear later in the StringBuffer are not guaranteed to have a higher line/column number. In fact, there are no guarantees whatsoever, as #line pragmas can arbitrarily modify locations. This lack of guarantees makes ideas such as #17544 infeasible. This patch adds an additional bit of information to every SrcLoc: newtype BufPos = BufPos { bufPos :: Int } A BufPos represents the location in the StringBuffer, unaffected by any pragmas. Updates haddock submodule. Metric Increase: haddock.Cabal haddock.base haddock.compiler MultiLayerModules Naperian parsing001 T12150
* Modules: Core (#13009)Sylvain Henry2020-02-262-3/+3
| | | | Update haddock submodule
* Remove Ord SrcLoc, Ord SrcSpanVladislav Zavialov2020-02-241-3/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Before this patch, GHC relied on Ord SrcSpan to identify source elements, by using SrcSpan as Map keys: blackList :: Map SrcSpan () -- compiler/GHC/HsToCore/Coverage.hs instanceMap :: Map SrcSpan Name -- compiler/GHC/HsToCore/Docs.hs Firstly, this design is not valid in presence of UnhelpfulSpan, as it distinguishes between UnhelpfulSpan "X" and UnhelpfulSpan "Y", but those strings are messages for the user, unfit to serve as identifiers for source elements. Secondly, this design made it hard to extend SrcSpan with additional data. Recall that the definition of SrcSpan is: data SrcSpan = RealSrcSpan !RealSrcSpan | UnhelpfulSpan !FastString Say we want to extend the RealSrcSpan constructor with additional information: data SrcSpan = RealSrcSpan !RealSrcSpan !AdditionalInformation | UnhelpfulSpan !FastString getAdditionalInformation :: SrcSpan -> AdditionalInformation getAdditionalInformation (RealSrcSpan _ a) = a Now, in order for Map SrcSpan to keep working correctly, we must *ignore* additional information when comparing SrcSpan values: instance Ord SrcSpan where compare (RealSrcSpan r1 _) (RealSrcSpan r2 _) = compare r1 r2 ... However, this would violate an important law: a == b therefore f a == f b Ignoring AdditionalInformation in comparisons would mean that with f=getAdditionalInformation, the law above does not hold. A more robust design is to avoid Ord SrcSpan altogether, which is what this patch implements. The mappings are changed to use RealSrcSpan instead: blackList :: Set RealSrcSpan -- compiler/GHC/HsToCore/Coverage.hs instanceMap :: Map RealSrcSpan Name -- compiler/GHC/HsToCore/Docs.hs All SrcSpan comparisons are now done with explicit comparison strategies: SrcLoc.leftmost_smallest SrcLoc.leftmost_largest SrcLoc.rightmost_smallest These strategies are not subject to the law mentioned above and can easily discard both the string stored in UnhelpfulSpan and AdditionalInformation. Updates haddock submodule.
* Modules: Driver (#13009)Sylvain Henry2020-02-216-26/+26
| | | | submodule updates: nofib, haddock
* Module hierarchy: HsToCore (cf #13009)Sylvain Henry2020-02-141-1/+1
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* Module hierarchy: ByteCode and Runtime (cf #13009)Sylvain Henry2020-02-123-8/+8
| | | | Update haddock submodule
* Fix GhcThreaded settingBen Gamari2020-02-081-0/+6
| | | | | | | | | | | | | | This adopts a patch from NetBSD's packaging fixing the `GhcThreaded` option of the make build system. In addition we introduce a `ghcThreaded` option in hadrian's `Flavour` type. Also fix Hadrian's treatment of the `Use Threaded` entry in `settings`. Previously it would incorrectly claim `Use Threaded = True` if we were building the `threaded` runtime way. However, this is inconsistent with the `make` build system, which defines it to be whether the `ghc` executable is linked against the threaded runtime. Fixes #17692.
* compiler: Qualify imports of Data.ListBen Gamari2020-02-081-1/+1
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* Introduce IsPass; refactor wrappers.Richard Eisenberg2020-02-081-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There are two main payloads of this patch: 1. This introduces IsPass, which allows e.g. printing code to ask what pass it is running in (Renamed vs Typechecked) and thus print extension fields. See Note [IsPass] in Hs.Extension 2. This moves the HsWrap constructor into an extension field, where it rightly belongs. This is done for HsExpr and HsCmd, but not for HsPat, which is left as an exercise for the reader. There is also some refactoring around SyntaxExprs, but this is really just incidental. This patch subsumes !1721 (sorry @chreekat). Along the way, there is a bit of refactoring in GHC.Hs.Extension, including the removal of NameOrRdrName in favor of NoGhcTc. This meant that we had no real need for GHC.Hs.PlaceHolder, so I got rid of it. Updates haddock submodule. ------------------------- Metric Decrease: haddock.compiler -------------------------
* Fix more typos, via an improved Levenshtein-style correctorBrian Wignall2020-01-122-4/+4
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* Module hierarchy: Iface (cf #13009)Sylvain Henry2020-01-062-3/+3
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* Remove HasSrcSpan (#17494)Vladislav Zavialov2019-11-301-7/+7
| | | | | Metric Decrease: haddock.compiler
* Fix typosBrian Wignall2019-11-231-1/+1
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* Bump Haskeline and add exceptions as boot libraryBen Gamari2019-11-132-16/+49
| | | | Haskeline now depends upon exceptions. See #16752.
* Remove redundant -fno-cse optionsÖmer Sinan Ağacan2019-10-262-5/+1
| | | | | These were probably added with some GLOBAL_VARs, but those GLOBAL_VARs are now gone.
* Fix #14690 - :steplocal panics after break-on-errorRoland Senn2019-10-261-0/+4
| | | | | | | | | | | | | | `:steplocal` enables only breakpoints in the current top-level binding. When a normal breakpoint is hit, then the module name and the break id from the `BRK_FUN` byte code allow us to access the corresponding entry in a ModBreak table. From this entry we then get the SrcSpan (see compiler/main/InteractiveEval.hs:bindLocalsAtBreakpoint). With this source-span we can then determine the current top-level binding, needed for the steplocal command. However, if we break at an exception or at an error, we don't have an BRK_FUN byte-code, so we don't have any source information. The function `bindLocalsAtBreakpoint` creates an `UnhelpfulSpan`, which doesn't allow us to determine the current top-level binding. To avoid a `panic`, we have to check for `UnhelpfulSpan` in the function `ghc/GHCi/UI.hs:stepLocalCmd`. Hence a :steplocal command after a break-on-exception or a break-on-error is not possible.
* Allow command name resolution for GHCi commands with option `!` #17345Takenobu Tani2019-10-231-5/+14
| | | | | | | | | | | | | | | | | | | | This commit allows command name resolution for GHCi commands with option `!` as follows: ghci> :k! Int Int :: * = Int This commit changes implementation as follows: Before: * Prefix match with full string including the option `!` (e.g. `k!`) After (this patch): * Prefix match without option suffix `!` (e.g. `k`) * in addition, suffix match with option `!` See also #8305 and #8113
* Compiling with -S and -fno-code no longer panics (fixes #17143)adithyaov2019-10-161-0/+4
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* Add GHCi help message for :def! and :: commandsTakenobu Tani2019-10-131-1/+3
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* Refactor, document, and optimize LLVM configuration loadingBen Gamari2019-10-071-6/+2
| | | | | | | | | | | | As described in the new Note [LLVM Configuration] in SysTools, we now load llvm-targets and llvm-passes lazily to avoid the overhead of doing so when -fllvm isn't used (also known as "the common case"). Noticed in #17003. Metric Decrease: T12234 T12150
* Always enable the external interpreterJohn Ericson2019-10-042-25/+31
| | | | | | You can always just not use or even build `iserv`. I don't think the maintenance cost of the CPP is worth...I can't even tell what the benefit is.
* Per stage headers, ghc_boot_platform.h -> stage 0 ghcplatform.hJohn Ericson2019-10-041-5/+0
| | | | | | | | | | | | | | | | | | The generated headers are now generated per stage, which means we can skip hacks like `ghc_boot_platform.h` and just have that be the stage 0 header as proper. In general, stages are to be embraced: freely generate everything in each stage but then just build what you depend on, and everything is symmetrical and efficient. Trying to avoid stages because bootstrapping is a mind bender just creates tons of bespoke mini-mind-benders that add up to something far crazier. Hadrian was pretty close to this "stage-major" approach already, and so was fairly easy to fix. Make needed more work, however: it did know about stages so at least there was a scaffold, but few packages except for the compiler cared, and the compiler used its own counting system. That said, make and Hadrian now work more similarly, which is good for the transition to Hadrian. The merits of embracing stage aside, the change may be worthy for easing that transition alone.
* Add help message for GHCi :instances commandTakenobu Tani2019-09-301-0/+1
| | | | This commit updates GHCi's help message for GHC 8.10.
* Refactor iface file generation:Ömer Sinan Ağacan2019-09-301-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This commit refactors interface file generation to allow information from the later passed (NCG, STG) to be stored in interface files. We achieve this by splitting interface file generation into two parts: * Partial interfaces, built based on the result of the core pipeline * A fully instantiated interface, which also contains the final fingerprints and can optionally contain information produced by the backend. This change is required by !1304 and !1530. -dynamic-too handling is refactored too: previously when generating code we'd branch on -dynamic-too *before* code generation, but now we do it after. (Original code written by @AndreasK in !1530) Performance ~~~~~~~~~~~ Before this patch interface files where created and immediately flushed to disk which made space leaks impossible. With this change we instead use NFData to force all iface related data structures to avoid space leaks. In the process of refactoring it was discovered that the code in the ToIface Module allocated a lot of thunks which were immediately forced when writing/forcing the interface file. So we made this module more strict to avoid creating many of those thunks. Bottom line is that allocations go down by about ~0.1% compared to master. Residency is not meaningfully different after this patch. Runtime was not benchmarked. Co-Authored-By: Andreas Klebinger <klebinger.andreas@gmx.at> Co-Authored-By: Ömer Sinan Ağacan <omer@well-typed.com>
* Module hierarchy: Hs (#13009)Sylvain Henry2019-09-202-4/+4
| | | | | | | Add GHC.Hs module hierarchy replacing hsSyn. Metric Increase: haddock.compiler
* Use lazyness for FastString's z-encoding memoizationDaniel Gröber2019-09-091-1/+1
| | | | | | | | | | | | | | | | | | | Having an IORef in FastString to memoize the z-encoded version is unecessary because there is this amazing thing Haskell can do natively, it's called "lazyness" :) We simply remove the UNPACK and strictness annotations from the constructor field corresponding to the z-encoding, making it lazy, and store the (pure) z-encoded string there. The only complication here is 'hasZEncoding' which allows cheking if a z-encoding was computed for a given string. Since this is only used for compiler performance statistics though it's not actually necessary to have the current per-string granularity. Instead I add a global IORef counter to the FastStringTable and use unsafePerformIO to increment the counter whenever a lazy z-encoding is forced.
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