1. 13 Jun, 2020 2 commits
    • Sylvain Henry's avatar
      Remove unused code · 7a02599a
      Sylvain Henry authored
    • Sylvain Henry's avatar
      DynFlags refactoring VIII (#17957) · 2517a51c
      Sylvain Henry authored
      * Remove several uses of `sdocWithDynFlags`, especially in GHC.Llvm.*
      * Add LlvmOpts datatype to store Llvm backend options
      * Remove Outputable instances (for LlvmVar, LlvmLit, LlvmStatic and
        Llvm.MetaExpr) which require LlvmOpts.
      * Rename ppMetaExpr into ppMetaAnnotExpr (pprMetaExpr is now used in place of `ppr :: MetaExpr -> SDoc`)
  2. 10 Jun, 2020 8 commits
    • Luke Lau's avatar
      Fix lookupGlobalOccRn_maybe sometimes reporting an error · 32fd37f5
      Luke Lau authored
      In some cases it was possible for lookupGlobalOccRn_maybe to return an
      error, when it should be returning a Nothing. If it called
      lookupExactOcc_either when there were no matching GlobalRdrElts in the
      otherwise case, it would return an error message. This could be caused
      when lookupThName_maybe in Template Haskell was looking in different
      namespaces (thRdrNameGuesses), guessing different namespaces that the
      name wasn't guaranteed to be found in.
      However, by addressing this some more accurate errors were being lost in
      the conversion to Maybes. So some of the lookup* functions have been
      shuffled about so that errors should always be ignored in
      lookup*_maybes, and propagated otherwise.
      This fixes #18263
    • Simon Peyton Jones's avatar
      Implement cast worker/wrapper properly · 6d49d5be
      Simon Peyton Jones authored
      The cast worker/wrapper transformation transforms
         x = e |> co
         y = e
         x = y |> co
      This is done by the simplifier, but we were being
      careless about transferring IdInfo from x to y,
      and about what to do if x is a NOINLNE function.
      This resulted in a series of bugs:
           #17673, #18093, #18078.
      This patch fixes all that:
      * Main change is in GHC.Core.Opt.Simplify, and
        the new prepareBinding function, which does this
        cast worker/wrapper transform.
        See Note [Cast worker/wrappers].
      * There is quite a bit of refactoring around
        prepareRhs, makeTrivial etc.  It's nicer now.
      * Some wrappers from strictness and cast w/w, notably those for
        a function with a NOINLINE, should inline very late. There
        wasn't really a mechanism for that, which was an existing bug
        really; so I invented a new finalPhase = Phase (-1).  It's used
        for all simplifier runs after the user-visible phase 2,1,0 have
        run.  (No new runs of the simplifier are introduced thereby.)
        See new Note [Compiler phases] in GHC.Types.Basic;
        the main changes are in GHC.Core.Opt.Driver
      * Doing this made me trip over two places where the AnonArgFlag on a
        FunTy was being lost so we could end up with (Num a -> ty)
        rather than (Num a => ty)
          - In coercionLKind/coercionRKind
          - In contHoleType in the Simplifier
        I fixed the former by defining mkFunctionType and using it in
        I could have done the same for the latter, but the information
        is almost to hand.  So I fixed the latter by
          - adding sc_hole_ty to ApplyToVal (like ApplyToTy),
          - adding as_hole_ty to ValArg (like TyArg)
          - adding sc_fun_ty to StrictArg
        Turned out I could then remove ai_type from ArgInfo.  This is
        just moving the deck chairs around, but it worked out nicely.
        See the new Note [AnonArgFlag] in GHC.Types.Var
      * When looking at the 'arity decrease' thing (#18093) I discovered
        that stable unfoldings had a much lower arity than the actual
        optimised function.  That's what led to the arity-decrease
        message.  Simple solution: eta-expand.
        It's described in Note [Eta-expand stable unfoldings]
        in GHC.Core.Opt.Simplify
      * I also discovered that unsafeCoerce wasn't being inlined if
        the context was boring.  So (\x. f (unsafeCoerce x)) would
        create a thunk -- yikes!  I fixed that by making inlineBoringOK
        a bit cleverer: see Note [Inline unsafeCoerce] in GHC.Core.Unfold.
        I also found that unsafeCoerceName was unused, so I removed it.
      I made a test case for #18078, and a very similar one for #17673.
      The net effect of all this on nofib is very modest, but positive:
              Program           Size    Allocs   Runtime   Elapsed  TotalMem
                 anna          -0.4%     -0.1%     -3.1%     -3.1%      0.0%
       fannkuch-redux          -0.4%     -0.3%     -0.1%     -0.1%      0.0%
             maillist          -0.4%     -0.1%     -7.8%     -1.0%    -14.3%
            primetest          -0.4%    -15.6%     -7.1%     -6.6%      0.0%
                  Min          -0.9%    -15.6%    -13.3%    -14.2%    -14.3%
                  Max          -0.3%      0.0%    +12.1%    +12.4%      0.0%
       Geometric Mean          -0.4%     -0.2%     -2.3%     -2.2%     -0.1%
      All following metric decreases are compile-time allocation decreases
      between -1% and -3%:
      Metric Decrease:
    • Simon Peyton Jones's avatar
      Optimisation in Unique.Supply · 9454511b
      Simon Peyton Jones authored
      This patch switches on -fno-state-hack in GHC.Types.Unique.Supply.
      It turned out that my fixes for #18078 (coercion floating) changed the
      optimisation pathway for mkSplitUniqSupply in such a way that we had
      an extra allocation inside the inner loop.  Adding -fno-state-hack
      fixed that -- and indeed the loop in mkSplitUniqSupply is a classic
      example of the way in which -fno-state-hack can be bad; see #18238.
      Moreover, the new code is better than the old.  They allocate
      the same, but the old code ends up with a partial application.
      The net effect is that the test
      runs 20% faster!   From 2.5s down to 2.0s.  The allocation numbers
      are the same -- but elapsed time falls. Good!
      The bad thing about this is that it's terribly delicate.  But
      at least it's a good example of such delicacy in action.
      There is a long Note [Optimising the unique supply] which now
      explains all this.
    • Shayne Fletcher's avatar
      Give Language a Bounded instance · 3b22b14a
      Shayne Fletcher authored
    • Ömer Sinan Ağacan's avatar
      Cross-module LambdaFormInfo passing · 7a737e89
      Ömer Sinan Ağacan authored
      - Store LambdaFormInfos of exported Ids in interface files
      - Use them in importing modules
      This is for optimization purposes: if we know LambdaFormInfo of imported
      Ids we can generate more efficient calling code, see `getCallMethod`.
      Exporting (putting them in interface files or in ModDetails) and
      importing (reading them from interface files) are both optional. We
      don't assume known LambdaFormInfos anywhere and do not change how we
      call Ids with unknown LambdaFormInfos.
      Runtime, allocation, and residency numbers when building
      Cabal-the-library (commit 0d4ee7ba3):
      (Log and .hp files are in the MR: !2842)
      |     | GHC HEAD | This patch | Diff           |
      | -O0 |  0:35.89 |    0:34.10 | -1.78s, -4.98% |
      | -O1 |  2:24.01 |    2:23.62 | -0.39s, -0.27% |
      | -O2 |  2:52.23 |    2:51.35 | -0.88s, -0.51% |
      |     | GHC HEAD        | This patch      | Diff                       |
      | -O0 |  54,843,608,416 |  54,878,769,544 |  +35,161,128 bytes, +0.06% |
      | -O1 | 227,136,076,400 | 227,569,045,168 | +432,968,768 bytes, +0.19% |
      | -O2 | 266,147,063,296 | 266,749,643,440 | +602,580,144 bytes, +0.22% |
      NOTE: Residency is measured with extra runtime args: `-i0 -h` which effectively
      turn all GCs into major GCs, and do GC more often.
      |     | GHC HEAD                   | This patch                   | Diff                       |
      | -O0 | 410,284,000 (910 samples)  | 411,745,008 (906 samples)    | +1,461,008 bytes, +0.35%   |
      | -O1 | 928,580,856 (2109 samples) | 943,506,552 (2103 samples)   | +14,925,696 bytes, +1.60%  |
      | -O2 | 993,951,352 (2549 samples) | 1,010,156,328 (2545 samples) | +16,204,9760 bytes, +1.63% |
      NoFib results:
              Program           Size    Allocs    Instrs     Reads    Writes
                   CS           0.0%      0.0%     +0.0%     +0.0%     +0.0%
                  CSD           0.0%      0.0%      0.0%     +0.0%     +0.0%
                   FS           0.0%      0.0%     +0.0%     +0.0%     +0.0%
                    S           0.0%      0.0%     +0.0%     +0.0%     +0.0%
                   VS           0.0%      0.0%     +0.0%     +0.0%     +0.0%
                  VSD           0.0%      0.0%     +0.0%     +0.0%     +0.1%
                  VSM           0.0%      0.0%     +0.0%     +0.0%     +0.0%
                 anna           0.0%      0.0%     -0.3%     -0.8%     -0.0%
                 ansi           0.0%      0.0%     -0.0%     -0.0%      0.0%
                 atom           0.0%      0.0%     -0.0%     -0.0%      0.0%
               awards           0.0%      0.0%     -0.1%     -0.3%      0.0%
               banner           0.0%      0.0%     -0.0%     -0.0%     -0.0%
           bernouilli           0.0%      0.0%     -0.0%     -0.0%     -0.0%
         binary-trees           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                boyer           0.0%      0.0%     -0.0%     -0.0%      0.0%
               boyer2           0.0%      0.0%     -0.0%     -0.0%      0.0%
                 bspt           0.0%      0.0%     -0.0%     -0.2%      0.0%
            cacheprof           0.0%      0.0%     -0.1%     -0.4%     +0.0%
             calendar           0.0%      0.0%     -0.0%     -0.0%      0.0%
             cichelli           0.0%      0.0%     -0.9%     -2.4%      0.0%
              circsim           0.0%      0.0%     -0.0%     -0.0%      0.0%
             clausify           0.0%      0.0%     -0.1%     -0.3%      0.0%
        comp_lab_zift           0.0%      0.0%     -0.0%     -0.0%     +0.0%
             compress           0.0%      0.0%     -0.0%     -0.0%     -0.0%
            compress2           0.0%      0.0%     -0.0%     -0.0%      0.0%
          constraints           0.0%      0.0%     -0.1%     -0.2%     -0.0%
         cryptarithm1           0.0%      0.0%     -0.0%     -0.0%      0.0%
         cryptarithm2           0.0%      0.0%     -1.4%     -4.1%     -0.0%
                  cse           0.0%      0.0%     -0.0%     -0.0%     -0.0%
         digits-of-e1           0.0%      0.0%     -0.0%     -0.0%     -0.0%
         digits-of-e2           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               dom-lt           0.0%      0.0%     -0.1%     -0.2%      0.0%
                eliza           0.0%      0.0%     -0.5%     -1.5%      0.0%
                event           0.0%      0.0%     -0.0%     -0.0%     -0.0%
          exact-reals           0.0%      0.0%     -0.1%     -0.3%     +0.0%
               exp3_8           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               expert           0.0%      0.0%     -0.3%     -1.0%     -0.0%
       fannkuch-redux           0.0%      0.0%     +0.0%     +0.0%     +0.0%
                fasta           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                  fem           0.0%      0.0%     -0.0%     -0.0%      0.0%
                  fft           0.0%      0.0%     -0.0%     -0.0%      0.0%
                 fft2           0.0%      0.0%     -0.0%     -0.0%      0.0%
             fibheaps           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                 fish           0.0%      0.0%      0.0%     -0.0%     +0.0%
                fluid           0.0%      0.0%     -0.4%     -1.2%     +0.0%
               fulsom           0.0%      0.0%     -0.0%     -0.0%      0.0%
               gamteb           0.0%      0.0%     -0.1%     -0.3%      0.0%
                  gcd           0.0%      0.0%     -0.0%     -0.0%      0.0%
          gen_regexps           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               genfft           0.0%      0.0%     -0.0%     -0.0%      0.0%
                   gg           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                 grep           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               hidden           0.0%      0.0%     -0.1%     -0.4%     -0.0%
                  hpg           0.0%      0.0%     -0.2%     -0.5%     +0.0%
                  ida           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                infer           0.0%      0.0%     -0.3%     -0.8%     -0.0%
              integer           0.0%      0.0%     -0.0%     -0.0%     +0.0%
            integrate           0.0%      0.0%     -0.0%     -0.0%      0.0%
         k-nucleotide           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                kahan           0.0%      0.0%     -0.0%     -0.0%     +0.0%
              knights           0.0%      0.0%     -2.2%     -5.4%      0.0%
               lambda           0.0%      0.0%     -0.6%     -1.8%      0.0%
           last-piece           0.0%      0.0%     -0.0%     -0.0%      0.0%
                 lcss           0.0%      0.0%     -0.0%     -0.1%      0.0%
                 life           0.0%      0.0%     -0.0%     -0.1%      0.0%
                 lift           0.0%      0.0%     -0.2%     -0.6%     +0.0%
               linear           0.0%      0.0%     -0.0%     -0.0%     -0.0%
            listcompr           0.0%      0.0%     -0.0%     -0.0%      0.0%
             listcopy           0.0%      0.0%     -0.0%     -0.0%      0.0%
             maillist           0.0%      0.0%     -0.1%     -0.3%     +0.0%
               mandel           0.0%      0.0%     -0.0%     -0.0%      0.0%
              mandel2           0.0%      0.0%     -0.0%     -0.0%     -0.0%
                 mate          +0.0%      0.0%     -0.0%     -0.0%     -0.0%
              minimax           0.0%      0.0%     -0.2%     -1.0%      0.0%
              mkhprog           0.0%      0.0%     -0.1%     -0.2%     -0.0%
           multiplier           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               n-body           0.0%      0.0%     -0.0%     -0.0%     +0.0%
             nucleic2           0.0%      0.0%     -0.1%     -0.2%      0.0%
                 para           0.0%      0.0%     -0.0%     -0.0%     -0.0%
            paraffins           0.0%      0.0%     -0.0%     -0.0%      0.0%
               parser           0.0%      0.0%     -0.2%     -0.7%      0.0%
              parstof           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                  pic           0.0%      0.0%     -0.0%     -0.0%      0.0%
             pidigits           0.0%      0.0%     +0.0%     +0.0%     +0.0%
                power           0.0%      0.0%     -0.2%     -0.6%     +0.0%
               pretty           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               primes           0.0%      0.0%     -0.0%     -0.0%      0.0%
            primetest           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               prolog           0.0%      0.0%     -0.3%     -1.1%      0.0%
               puzzle           0.0%      0.0%     -0.0%     -0.0%      0.0%
               queens           0.0%      0.0%     -0.0%     -0.0%     +0.0%
              reptile           0.0%      0.0%     -0.0%     -0.0%      0.0%
      reverse-complem           0.0%      0.0%     -0.0%     -0.0%     +0.0%
              rewrite           0.0%      0.0%     -0.7%     -2.5%     -0.0%
                 rfib           0.0%      0.0%     -0.0%     -0.0%      0.0%
                  rsa           0.0%      0.0%     -0.0%     -0.0%      0.0%
                  scc           0.0%      0.0%     -0.1%     -0.2%     -0.0%
                sched           0.0%      0.0%     -0.0%     -0.0%     -0.0%
                  scs           0.0%      0.0%     -1.0%     -2.6%     +0.0%
               simple           0.0%      0.0%     +0.0%     -0.0%     +0.0%
                solid           0.0%      0.0%     -0.0%     -0.0%      0.0%
              sorting           0.0%      0.0%     -0.6%     -1.6%      0.0%
        spectral-norm           0.0%      0.0%     +0.0%      0.0%     +0.0%
               sphere           0.0%      0.0%     -0.0%     -0.0%     -0.0%
               symalg           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                  tak           0.0%      0.0%     -0.0%     -0.0%      0.0%
            transform           0.0%      0.0%     -0.0%     -0.0%      0.0%
             treejoin           0.0%      0.0%     -0.0%     -0.0%      0.0%
            typecheck           0.0%      0.0%     -0.0%     -0.0%     +0.0%
              veritas          +0.0%      0.0%     -0.2%     -0.4%     +0.0%
                 wang           0.0%      0.0%     -0.0%     -0.0%      0.0%
            wave4main           0.0%      0.0%     -0.0%     -0.0%     -0.0%
         wheel-sieve1           0.0%      0.0%     -0.0%     -0.0%     -0.0%
         wheel-sieve2           0.0%      0.0%     -0.0%     -0.0%     +0.0%
                 x2n1           0.0%      0.0%     -0.0%     -0.0%     -0.0%
                  Min           0.0%      0.0%     -2.2%     -5.4%     -0.0%
                  Max          +0.0%      0.0%     +0.0%     +0.0%     +0.1%
       Geometric Mean          -0.0%     -0.0%     -0.1%     -0.3%     +0.0%
      Metric increases micro benchmarks tracked in #17686:
      Metric Increase:
      Co-authored-by: Andreas Klebinger's avatarAndreas Klebinger <klebinger.andreas@gmx.at>
    • Shayne Fletcher's avatar
    • Takenobu Tani's avatar
      Clarify leaf module names for new module hierarchy · 24879129
      Takenobu Tani authored
      This updates comments only.
      This patch replaces leaf module names according to new module
      hierarchy [1][2] as followings:
      * Expand leaf names to easily find the module path:
        for instance, `Id.hs` to `GHC.Types.Id`.
      * Modify leaf names according to new module hierarchy:
        for instance, `Convert.hs` to `GHC.ThToHs`.
      * Fix typo:
        for instance, `GHC.Core.TyCo.Rep.hs` to `GHC.Core.TyCo.Rep`
      See also !3375
      [1]: https://gitlab.haskell.org/ghc/ghc/-/wikis/Make-GHC-codebase-more-modular
      [2]: #13009
    • Ryan Scott's avatar
      Always use rnImplicitBndrs to bring implicit tyvars into scope · a47e6442
      Ryan Scott authored
      This implements a first step towards #16762 by changing the renamer
      to always use `rnImplicitBndrs` to bring implicitly bound type
      variables into scope. The main change is in `rnFamInstEqn` and
      `bindHsQTyVars`, which previously used _ad hoc_ methods of binding
      their implicit tyvars.
      There are a number of knock-on consequences:
      * One of the reasons that `rnFamInstEqn` used an _ad hoc_ binding
        mechanism was to give more precise source locations in
        `-Wunused-type-patterns` warnings. (See
        #16762 (comment 273343) for an
        example of this.) However, these warnings are actually a little
        _too_ precise, since implicitly bound type variables don't have
        exact binding sites like explicitly bound type variables do.
        A similar problem existed for
        "`Different names for the same type variable`" errors involving
        implicit tyvars bound by `bindHsQTyVars`.
        Therefore, we simply accept the less precise (but more accurate)
        source locations from `rnImplicitBndrs` in `rnFamInstEqn` and
        `bindHsQTyVars`. See
        `Note [Source locations for implicitly bound type variables]` in
        `GHC.Rename.HsType` for the full story.
      * In order for `rnImplicitBndrs` to work in `rnFamInstEqn`, it needs
        to be able to look up names from the parent class (in the event
        that we are renaming an associated type family instance). As a
        result, `rnImplicitBndrs` now takes an argument of type
        `Maybe assoc`, which is `Just` in the event that a type family
        instance is associated with a class.
      * Previously, GHC kept track of three type synonyms for free type
        variables in the renamer: `FreeKiTyVars`, `FreeKiTyVarsDups`
        (which are allowed to contain duplicates), and
        `FreeKiTyVarsNoDups` (which contain no duplicates). However, making
        is a distinction between `-Dups` and `-NoDups` is now pointless, as
        all code that returns `FreeKiTyVars{,Dups,NoDups}` will eventually
        end up being passed to `rnImplicitBndrs`, which removes duplicates.
        As a result, I decided to just get rid of `FreeKiTyVarsDups` and
        `FreeKiTyVarsNoDups`, leaving only `FreeKiTyVars`.
      * The `bindLRdrNames` and `deleteBys` functions are now dead code, so
        I took the liberty of removing them.
  3. 09 Jun, 2020 1 commit
    • Ryan Scott's avatar
      Make GADT constructors adhere to the forall-or-nothing rule properly · 72c7fe9a
      Ryan Scott authored
      Issue #18191 revealed that the types of GADT constructors don't quite
      adhere to the `forall`-or-nothing rule. This patch serves to clean up
      this sad state of affairs somewhat. The main change is not in the
      code itself, but in the documentation, as this patch introduces two
      sections to the GHC User's Guide:
      * A "Formal syntax for GADTs" section that presents a BNF-style
        grammar for what is and isn't allowed in GADT constructor types.
        This mostly exists to codify GHC's existing behavior, but it also
        imposes a new restriction that addresses #18191: the outermost
        `forall` and/or context in a GADT constructor is not allowed to be
        surrounded by parentheses. Doing so would make these
        `forall`s/contexts nested, and GADTs do not support nested
        `forall`s/contexts at present.
      * A "`forall`-or-nothing rule" section that describes exactly what
        the `forall`-or-nothing rule is all about. Surprisingly, there was
        no mention of this anywhere in the User's Guide up until now!
      To adhere the new specification in the "Formal syntax for GADTs"
      section of the User's Guide, the following code changes were made:
      * A new function, `GHC.Hs.Type.splitLHsGADTPrefixTy`, was introduced.
        This is very much like `splitLHsSigmaTy`, except that it avoids
        splitting apart any parentheses, which can be syntactically
        significant for GADT types. See
        `Note [No nested foralls or contexts in GADT constructors]` in
      * `ConDeclGADTPrefixPs`, an extension constructor for `XConDecl`, was
        introduced so that `GHC.Parser.PostProcess.mkGadtDecl` can return
        it when given a prefix GADT constructor. Unlike `ConDeclGADT`,
        `ConDeclGADTPrefixPs` does not split the GADT type into its argument
        and result types, as this cannot be done until after the type is
        renamed (see `Note [GADT abstract syntax]` in `GHC.Hs.Decls` for why
        this is the case).
      * `GHC.Renamer.Module.rnConDecl` now has an additional case for
        `ConDeclGADTPrefixPs` that (1) splits apart the full `LHsType` into
        its `forall`s, context, argument types, and result type, and
        (2) checks for nested `forall`s/contexts. Step (2) used to be
        performed the typechecker (in `GHC.Tc.TyCl.badDataConTyCon`) rather
        than the renamer, but now the relevant code from the typechecker
        can simply be deleted.
        One nice side effect of this change is that we are able to give a
        more accurate error message for GADT constructors that use visible
        dependent quantification (e.g., `MkFoo :: forall a -> a -> Foo a`),
        which improves the stderr in the `T16326_Fail6` test case.
      Fixes #18191. Bumps the Haddock submodule.
  4. 07 Jun, 2020 2 commits
    • Ben Gamari's avatar
      OccurAnal: Avoid exponential behavior due to where clauses · f1bfb806
      Ben Gamari authored
      Previously the `Var` case of `occAnalApp` could in some cases (namely
      in the case of `runRW#` applications) call `occAnalRhs` two. In the case
      of nested `runRW#`s this results in exponential complexity. In some
      cases the compilation time that resulted would be very long indeed
      (see #18296).
      Fixes #18296.
      Metric Decrease:
    • Moritz Angermann's avatar
      Disable DLL loading if without system linker · 6dae6548
      Moritz Angermann authored
      Some platforms (musl, aarch64) do not have a working dynamic linker
      implemented in the libc, even though we might see dlopen.  It will
      ultimately just return that this is not supported.  Hence we'll add
      a flag to the compiler to flat our disable loading dlls.  This is
      needed as we will otherwise try to load the shared library even
      if this will subsequently fail.  At that point we have given up
      looking for static options though.
  5. 05 Jun, 2020 2 commits
    • Ryan Scott's avatar
      Simplify bindLHsTyVarBndrs and bindHsQTyVars · 2dff8141
      Ryan Scott authored
      Both `bindLHsTyVarBndrs` and `bindHsQTyVars` take two separate
      `Maybe` arguments, which I find terribly confusing. Thankfully, it's
      possible to remove one `Maybe` argument from each of these functions,
      which this patch accomplishes:
      * `bindHsQTyVars` takes a `Maybe SDoc` argument, which is `Just` if
        GHC should warn about any of the quantified type variables going
        unused. However, every call site uses `Nothing` in practice. This
        makes sense, since it doesn't really make sense to warn about
        unused type variables bound by an `LHsQTyVars`. For instance, you
        wouldn't warn about the `a` in `data Proxy a = Proxy` going unused.
        As a result, I simply remove this `Maybe SDoc` argument altogether.
      * `bindLHsTyVarBndrs` also takes a `Maybe SDoc` argument for the same
        reasons that `bindHsQTyVars` took one. To make things more
        confusing, however, `bindLHsTyVarBndrs` also takes a separate
        `HsDocContext` argument, which is pretty-printed (to an `SDoc`) in
        warnings and error messages.
        In practice, the `Maybe SDoc` and the `HsDocContext` often contain
        the same text. See the call sites for `bindLHsTyVarBndrs` in
        `rnFamInstEqn` and `rnConDecl`, for instance. There are only a
        handful of call sites where the text differs between the
        `Maybe SDoc` and `HsDocContext` arguments:
        * In `rnHsRuleDecl`, where the `Maybe SDoc` says "`In the rule`"
          and the `HsDocContext` says "`In the transformation rule`".
        * In `rnHsTyKi`/`rn_ty`, where the `Maybe SDoc` says
          "`In the type`" but the `HsDocContext` is inhereted from the
          surrounding context (e.g., if `rnHsTyKi` were called on a
          top-level type signature, the `HsDocContext` would be
          "`In the type signature`" instead)
        In both cases, warnings/error messages arguably _improve_ by
        unifying making the `Maybe SDoc`'s text match that of the
        `HsDocContext`. As a result, I decided to remove the `Maybe SDoc`
        argument to `bindLHsTyVarBndrs` entirely and simply reuse the text
        from the `HsDocContext`. (I decided to change the phrase
        "transformation rule" to "rewrite rule" while I was in the area.)
        The `Maybe SDoc` argument has one other purpose: signaling when to
        emit "`Unused quantified type variable`" warnings. To recover this
        functionality, I replaced the `Maybe SDoc` argument with a
        boolean-like `WarnUnusedForalls` argument. The only
        `bindLHsTyVarBndrs` call site that chooses _not_ to emit these
        warnings in `bindHsQTyVars`.
    • Simon Peyton Jones's avatar
      Simple subsumption · 2b792fac
      Simon Peyton Jones authored
      This patch simplifies GHC to use simple subsumption.
        Ticket #17775
      Implements GHC proposal #287
      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
        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:
      * 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:
      Metric Decrease:
      Merge note: This appears to break the
      `UnliftedNewtypesDifficultUnification` test. It has been marked as
      broken in the interest of merging.
      (cherry picked from commit 66b7b195)
  6. 04 Jun, 2020 4 commits
    • Ben Gamari's avatar
    • Ben Gamari's avatar
      GHC.Hs.Instances: Compile with -O0 · 6735b9d9
      Ben Gamari authored
      This module contains exclusively Data instances, which are going to be
      slow no matter what we do. Furthermore, they are incredibly slow to
      compile with optimisation (see #9557). Consequently we compile this with
      -O0.  See #18254.
    • Luke Lau's avatar
      Fix documentation on type families not being extracted · 2bd3929a
      Luke Lau authored
      It looks like the location of the Names used for CoAxioms on type
      families are now located at their type constructors. Previously, Docs.hs
      thought the Names were located in the RHS, so the RealSrcSpan in the
      instanceMap and getInstLoc didn't match up. Fixes #18241
    • John Ericson's avatar
      Clean up boot vs non-boot disambiguating types · 32a4ae90
      John Ericson authored
      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
      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
      Updates `haddock` submodule.
  7. 01 Jun, 2020 10 commits
  8. 30 May, 2020 3 commits
    • wz1000's avatar
      Simplify contexts in GHC.Iface.Ext.Ast · 6947231a
      wz1000 authored
    • Andreas Klebinger's avatar
      Optimize GHC.Utils.Monad. · 7c555b05
      Andreas Klebinger authored
      Many functions in this module are recursive and as such are marked
      loop breakers. Which means they are unlikely to get an unfolding.
      This is *bad*. We always want to specialize them to specific Monads.
      Which requires a visible unfolding at the use site.
      I rewrote the recursive ones from:
          foo f x = ... foo x' ...
          foo f x = go x
              go x = ...
      As well as giving some pragmas to make all of them available
      for specialization.
      The end result is a reduction of allocations of about -1.4% for
      nofib/spectral/simple/Main.hs when compiled with `-O`.
      Metric Decrease:
    • Peter Trommler's avatar
      PPC NCG: Fix .size directive on powerpc64 ELF v1 · 7f8f948c
      Peter Trommler authored
      Thanks to Sergei Trofimovich for pointing out the issue.
      Fixes #18237
  9. 29 May, 2020 7 commits
    • Peter Trommler's avatar
      PPC NCG: No per-symbol .section ".toc" directives · aac19e6c
      Peter Trommler authored
      All position independent symbols are collected during code generation
      and emitted in one go. Prepending each symbol with a .section ".toc"
      directive is redundant. This patch drops the per-symbol directives
      leading to smaller assembler files.
      Fixes #18250
    • Ben Gamari's avatar
      Eta expand un-saturated primops · 277c2f26
      Ben Gamari authored
      Now since we no longer try to predict CAFfyness we have no need for the
      solution to #16846. Eta expanding unsaturated primop applications is
      conceptually simpler, especially in the presence of levity polymorphism.
      This essentially reverts cac8dc9f,
      as suggested in #18079.
      Closes #18079.
    • Ben Gamari's avatar
      Allow simplification through runRW# · 46720997
      Ben Gamari authored
      Because runRW# inlines so late, we were previously able to do very
      little simplification across it. For instance, given even a simple
      program like
          case runRW# (\s -> let n = I# 42# in n) of
            I# n# -> f n#
      we previously had no way to avoid the allocation of the I#.
      This patch allows the simplifier to push strict contexts into the
      continuation of a runRW# application, as explained in
      in Note [Simplification of runRW#] in GHC.CoreToStg.Prep.
      Fixes #15127.
      Metric Increase:
      Metric Decrease:
      Co-Authored-By: Simon Peyton Jones's avatarSimon Peyton-Jone <simonpj@microsoft.com>
    • Simon Peyton Jones's avatar
      Do not float join points in exprIsConApp_maybe · c49f7df0
      Simon Peyton Jones authored
      We hvae been making exprIsConApp_maybe cleverer in recent times:
          commit b78cc64e
          Date:   Thu Nov 15 17:14:31 2018 +0100
          Make constructor wrappers inline only during the final phase
          commit 7833cf40
          Date:   Thu Jan 24 17:58:50 2019 +0100
          Look through newtype wrappers (Trac #16254)
          commit c25b135f
          Date:   Thu Feb 21 12:03:22 2019 +0000
          Fix exprIsConApp_maybe
      But alas there was still a bug, now immortalised in
        Note [Don't float join points]
      in SimpleOpt.
      It's quite hard to trigger because it requires a dead
      join point, but it came up when compiling Cabal
      Cabal.Distribution.Fields.Lexer.hs, when working on
      Happily, the fix is extremly easy.  Finding the
      bug was not so easy.
    • Simon Peyton Jones's avatar
      Make Lint check return type of a join point · 0e3361ca
      Simon Peyton Jones authored
         join x = rhs in body
      It's important that the type of 'rhs' is the same as the type of
      'body', but Lint wasn't checking that invariant.
      Now it does!  This was exposed by investigation into !3113.
    • Ben Gamari's avatar
      CoreToStg: Add Outputable ArgInfo instance · bbeb2389
      Ben Gamari authored
    • Andreas Klebinger's avatar
      Fix "build/elem" RULE. · f10d11fa
      Andreas Klebinger authored
      An redundant constraint prevented the rule from matching.
      Fixing this allows a call to elem on a known list to be translated
      into a series of equality checks, and eventually a simple case
      Surprisingly this seems to regress elem for strings. To avoid
      this we now also allow foldrCString to inline and add an UTF8
      variant. This results in elem being compiled to a tight
      non-allocating loop over the primitive string literal which
      performs a linear search.
      In the process this commit adds UTF8 variants for some of the
      functions in GHC.CString. This is required to make this work for
      both ASCII and UTF8 strings.
      There are also small tweaks to the CString related rules.
      We now allow ourselfes the luxury to compare the folding function
      via eqExpr, which helps to ensure the rule fires before we inline
      foldrCString*. Together with a few changes to allow matching on both
      the UTF8 and ASCII variants of the CString functions.
  10. 28 May, 2020 1 commit