- Mar 12, 2020
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Issue #17880 demonstrates that `DeriveFunctor`-generated code is surprisingly fragile when rank-_n_ types are involved. The culprit is that `$fmap` (the algorithm used to generate `fmap` implementations) was too keen on applying arguments with rank-_n_ types to lambdas, which fail to typecheck more often than not. In this patch, I change `$fmap` (both the specification and the implementation) to produce code that avoids creating as many lambdas, avoiding problems when rank-_n_ field types arise. See the comments titled "Functor instances" in `TcGenFunctor` for a more detailed description. Not only does this fix #17880, but it also ensures that the code that `DeriveFunctor` generates will continue to work after simplified subsumption is implemented (see #17775). What is truly amazing is that #17880 is actually a regression (introduced in GHC 7.6.3) caused by commit 49ca2a37, the fix #7436. Prior to that commit, the version of `$fmap` that was used was almost identical to the one used in this patch! Why did that commit change `$fmap` then? It was to avoid severe performance issues that would arise for recursive `fmap` implementations, such as in the example below: ```hs data List a = Nil | Cons a (List a) deriving Functor -- ===> instance Functor List where fmap f Nil = Nil fmap f (Cons x xs) = Cons (f x) (fmap (\y -> f y) xs) ``` The fact that `\y -> f y` was eta expanded caused significant performance overheads. Commit 49ca2a37 fixed this performance issue, but it went too far. As a result, this patch partially reverts 49ca2a37. To ensure that the performance issues pre-#7436 do not resurface, I have taken some precautionary measures: * I have added a special case to `$fmap` for situations where the last type variable in an application of some type occurs directly. If this special case fires, we avoid creating a lambda expression. This ensures that we generate `fmap f (Cons x xs) = Cons (f x) (fmap f xs)` in the derived `Functor List` instance above. For more details, see `Note [Avoid unnecessary eta expansion in derived fmap implementations]` in `TcGenFunctor`. * I have added a `T7436b` test case to ensure that the performance of this derived `Functor List`-style code does not regress. When implementing this, I discovered that `$replace`, the algorithm which generates implementations of `(<$)`, has a special case that is very similar to the `$fmap` special case described above. `$replace` marked this special case with a custom `Replacer` data type, which was a bit overkill. In order to use the same machinery for both `Functor` methods, I ripped out `Replacer` and instead implemented a simple way to detect the special case. See the updated commentary in `Note [Deriving <$]` for more details.
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Should make `member` queries faster and avoid messing up with missing `nubSort`. Metric Increase: hie002 -
* `interpreterDynamic` and `interpreterProfiled` now take `Interp` parameters instead of DynFlags * slight refactoring of `ExternalInterp` so that we can read the iserv configuration (which is pure) without reading an MVar.
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* 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.
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- Mar 11, 2020
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In copying GC, with the relevant debug flags enabled, we release the old blocks after a GC, and the block allocator zeroes the space before releasing a block. This effectively zeros the old heap. In compacting GC we reuse the blocks and previously we didn't zero the unused space in a compacting generation after compaction. With this patch we zero the slop between the free pointer and the end of the block when we're done with compaction and when switching to a new block (because the current block doesn't have enough space for the next object we're shifting).
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I see quite a few warnings like: WARNING: file compiler/utils/Util.hs, line 593 Over-long elem in unionLists But the call stack is uninformative. Better to add HasDebugCallStack to isIn. Ditto isn'tIn. -
As noted in #17018. Also fix fragile declaration of T13786, which only runs in the normal way.
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Previously, `tcRules` would check for naughty quantification candidates (see `Note [Naughty quantification candidates]` in `TcMType`) when generalising over the type of a rewrite rule. This caused sensible-looking rewrite rules (like those in #17710) to be rejected. A more permissing (and easier-to-implement) approach is to do what is described in `Note [Generalising in tcTyFamInstEqnGuts]` in `TcTyClsDecls`: just re-quantify all the type variable binders, regardless of the order in which the user specified them. After all, the notion of type variable specificity has no real meaning in rewrite rules, since one cannot "visibly apply" a rewrite rule. I have written up this wisdom in `Note [Re-quantify type variables in rules]` in `TcRules`. As a result of this patch, compiling the `ExplicitForAllRules1` test case now generates one fewer warning than it used to. As far as I can tell, this is benign, since the thing that the disappearing warning talked about was also mentioned in an entirely separate warning. Fixes #17710.
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* GHC.Iface.Recomp: recompilation avoidance stuff * GHC.Iface.Make: mkIface* Moved `writeIfaceFile` into GHC.Iface.Load alongside `readIface` and renamed it `writeIface` for consistency.
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macOS Catalina now supports a non-POSIX-compliant version of clock_gettime which cannot use the clock_gettime codepath. Fixes #17906.
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- Mar 10, 2020
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Krzysztof Gogolewski authored
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- Remove Note [Existentials in shift_con_pat]. The function shift_con_pat has been removed 15 years ago in 23f40f0e. - Remove kcLookupTcTyCon - it's the same as tcLookupTcTyCon - Remove ASSERT in tyConAppArgN. It's already done by getNth, and it's the only reason getNth exists. - Remove unused function nextRole
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Clarify code added in #17852 and MR !2724
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When developing a plugin I had a shadowing problem, where I generated code app = \f{v r7B} x{v r7B} -> f{v r7B} x{v r7B} This is obviously wrong, since the occurrence of `f` to the right of the arrow refers to the `x` binder (they share a Unique). However, it is rather confusing when Lint reports Mismatch in type between binder and occurrence Var: x{v rB7} since it is printing the binder, rather than the occurrence. It is rather easy to read this as claiming there is something wrong with the `x` occurrence! We change the report to explicitly print both the binder and the occurrence variables. -
Previously, anyRewritableTyVar looked only at the arg and res of `arg -> res`, but their RuntimeReps are also subject to rewriting. Easy to fix. Test case: typecheck/should_compile/T17024 Fixes #17024.
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Closes #17904
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This isn't pretty but it's perhaps better than nothing.
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This fixes #17786, where the error parser fails to correctly handle the drive name in absolute Windows paths. Unfortunately I couldn't find a satisfactory way to test this.
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- Mar 09, 2020
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Aside from making the generated code easier to read when `-ddump-deriv` is enabled, this makes the error message in `T15073` substantially simpler (see the updated `T15073` expected stderr). Fixes #17899.
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Previously sparks living in the non-moving heap would be promptly GC'd by the minor collector since pruneSparkQueue uses the BF_EVACUATED flag, which non-moving heap blocks do not have set. Fix this by implementing proper support in pruneSparkQueue for determining reachability in the non-moving heap. The story is told in Note [Spark management in the nonmoving heap].
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- Mar 05, 2020
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- Mar 04, 2020
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Andreas Klebinger authoredThis fixes #17893 [skip-ci]
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- Mar 02, 2020
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If ImpredicativeTypes is not enabled, then `:print <term>` will fail if the type of <term> has nested `forall`s or `=>`s. This is because the GHCi debugger's internals will attempt to unify a metavariable with the type of <term> and then display the result, but if the type has nested `forall`s or `=>`s, then unification will fail. As a result, `:print` will bail out and the unhelpful result will be `<term> = (_t1::t1)` (where `t1` is a metavariable). Beware: <term> can have nested `forall`s even if its definition doesn't use RankNTypes! Here is an example from #14828: class Functor f where fmap :: (a -> b) -> f a -> f b Somewhat surprisingly, `:print fmap` considers the type of fmap to have nested foralls. This is because the GHCi debugger sees the type `fmap :: forall f. Functor f => forall a b. (a -> b) -> f a -> f b`. We could envision deeply instantiating this type to get the type `forall f a b. Functor f => (a -> b) -> f a -> f b`, but this trick wouldn't work for higher-rank types. Instead, we adopt a simpler fix: enable `ImpredicativeTypes` when using `:print` and friends in the GHCi debugger. This is allows metavariables to unify with types that have nested (or higher-rank) `forall`s/`=>`s, which makes `:print fmap` display as `fmap = (_t1::forall a b. Functor f => (a -> b) -> f a -> f b)`, as expected. Although ImpredicativeTypes is a somewhat unpredictable from a type inference perspective, there is no danger in using it in the GHCi debugger, since all of the terms that the GHCi debugger deals with have already been typechecked.
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Do not define hs_atomicread64() and hs_atomicwrite64() on machines where WORD_SIZE_IN_BITS is less than 64, just like we do with the rest of the atomic functions which work on 64-bit values. Without this, compilation fails on MIPSel and PowerPC with the following error: /usr/bin/ld: /<<PKGBUILDDIR>>/libraries/ghc-prim/dist-install/build/libHSghc-prim-0.5.3_p.a(atomic.p_o): in function `hs_atomicread64': atomic.c:(.text.hs_atomicread64+0x8): undefined reference to `__sync_add_and_fetch_8' /usr/bin/ld: /<<PKGBUILDDIR>>/libraries/ghc-prim/dist-install/build/libHSghc-prim-0.5.3_p.a(atomic.p_o): in function `hs_atomicwrite64': atomic.c:(.text.hs_atomicwrite64+0x38): undefined reference to `__sync_bool_compare_and_swap_8' Fixes #17886.
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* The names in PrelName and THNames are no longer used since TH merged types and kinds, Typeable is kind-polymorphic, .net support was removed * unqualQuasiQuote no longer used since 6f8ff0bb
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- Feb 29, 2020
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Roland Senn authored
GHCi is split up into 2 major parts: The user-interface (UI) and the byte-code interpreter. With `-fexternal-interpreter` they even run in different processes. Communication between the UI and the Interpreter (called `iserv`) is done using messages over a pipe. This is called `Remote GHCI` and explained in the Note [Remote GHCi] in `compiler/ghci/GHCi.hs`. To process a `:force` command the UI sends a `Seq` message to the `iserv` process. Then `iserv` does the effective evaluation of the value. When during this process a breakpoint is hit, the `iserv` process has no additional information to enhance the `Ignoring breakpoint` output with the breakpoint location. To be able to print additional breakpoint information, there are 2 possible implementation choices: 1. Store the needed information in the `iserv` process. 2. Print the `Ignoring breakpoint` from the UI process. For option 1 we need to store the breakpoint info redundantely in 2 places and this is bad. Therfore option 2 was implemented in this MR: - The user enters a `force` command - The UI sends a `Seq` message to the `iserv` process. - If processing of the `Seq` message hits a breakpoint, the `iserv` process returns control to the UI process. - The UI looks up the source location of the breakpoint, and prints the enhanced `Ignoring breakpoint` output. - The UI sends a `ResumeSeq` message to the `iserv` process, to continue forcing.
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IfaceIdInfo type is confusing: there's practically no difference between `NoInfo` and `HasInfo []`. The comments say NoInfo is used when -fomit-interface-pragmas is enabled, but we don't need to distinguish `NoInfo` from `HasInfo []` in when reading the interface so the distinction is not important. This patch simplifies the type by removing NoInfo. When we have no info we use an empty list. With this change we no longer read the info list lazily when reading an IfaceInfoItem, but when reading an IfaceId the ifIdInfo field is read lazily, so I doubt this is going to be a problem.
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