[Git][ghc/ghc][wip/T17775] 12 commits: rts: Enable tracing of nonmoving heap census with -ln

Simon Peyton Jones gitlab at gitlab.haskell.org
Mon May 4 11:01:53 UTC 2020 


Simon Peyton Jones pushed to branch wip/T17775 at Glasgow Haskell Compiler / GHC


Commits:
7bfe9ac5 by Ben Gamari at 2020-05-03T04:41:33-04:00
rts: Enable tracing of nonmoving heap census with -ln

Previously this was not easily available to the user. Fix this.
Non-moving collection lifecycle events are now reported with -lg.

- - - - -
c560dd07 by Ben Gamari at 2020-05-03T04:41:33-04:00
users guide: Move eventlog documentation users guide

- - - - -
02543d5e by Ben Gamari at 2020-05-03T04:41:33-04:00
users guide: Add documentation for non-moving GC events

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b465dd45 by Alexis King at 2020-05-03T04:42:12-04:00
Flatten nested casts in the simple optimizer

Normally, we aren’t supposed to generated any nested casts, since mkCast
takes care to flatten them, but the simple optimizer didn’t use mkCast,
so they could show up after inlining. This isn’t really a problem, since
the simplifier will clean them up immediately anyway, but it can clutter
the -ddump-ds output, and it’s an extremely easy fix.

closes #18112

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8bdc03d6 by Simon Peyton Jones at 2020-05-04T01:56:59-04:00
Don't return a panic in tcNestedSplice

In GHC.Tc.Gen.Splice.tcNestedSplice we were returning a
typechecked expression of "panic". That is usually OK, because
the result is discarded.  But it happens that tcApp now looks at
the typechecked expression, trivially, to ask if it is tagToEnum.
So being bottom is bad.

Moreover a debug-trace might print it out.

So better to return a civilised expression, even though it is
usually discarded.

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0bf640b1 by Baldur Blöndal at 2020-05-04T01:57:36-04:00
Don't require parentheses around via type (`-XDerivingVia'). Fixes #18130".

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26aedf3d by Simon Peyton Jones at 2020-05-04T11:18:15+01:00
Simple subsumption

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

* isTauTy: was replying True for (Show a => a ->a), which is utterly
  bogus.  Fixed.

* 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

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a6b1ee08 by Simon Peyton Jones at 2020-05-04T11:18:16+01:00
Wibbles

Especially make major improvement to hsWrapDictBinders

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3310af0c by Simon Peyton Jones at 2020-05-04T11:18:16+01:00
Wibbles

esp to tcPolyCheck

- - - - -
52089110 by Simon Peyton Jones at 2020-05-04T11:18:16+01:00
Wibbles

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54d93222 by Simon Peyton Jones at 2020-05-04T11:18:16+01:00
Wibbles

- - - - -
188205d6 by Simon Peyton Jones at 2020-05-04T12:01:25+01:00
Wibbles (dynamic-paper ticks)

- - - - -


23 changed files:

- compiler/GHC/Builtin/Names.hs
- compiler/GHC/Builtin/Types.hs
- compiler/GHC/Core/Coercion.hs
- compiler/GHC/Core/SimpleOpt.hs
- compiler/GHC/Core/Type.hs
- compiler/GHC/Driver/Main.hs
- compiler/GHC/Hs/Binds.hs
- compiler/GHC/Hs/Types.hs
- compiler/GHC/HsToCore/Binds.hs
- compiler/GHC/HsToCore/PmCheck.hs
- compiler/GHC/Iface/Load.hs
- compiler/GHC/Parser.y
- compiler/GHC/Rename/HsType.hs
- compiler/GHC/Rename/Splice.hs
- compiler/GHC/Tc/Errors.hs
- compiler/GHC/Tc/Errors/Hole.hs
- compiler/GHC/Tc/Gen/Arrow.hs
- compiler/GHC/Tc/Gen/Bind.hs
- compiler/GHC/Tc/Gen/Default.hs
- compiler/GHC/Tc/Gen/Expr.hs
- compiler/GHC/Tc/Gen/Expr.hs-boot
- compiler/GHC/Tc/Gen/Foreign.hs
- compiler/GHC/Tc/Gen/HsType.hs


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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/b4d28d52e62db37a11f58a4c035d5414c4ed9209...188205d687bac490ed8bd7a038569aca15c25a68

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