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  1. Jul 02, 2021
    • Sylvain Henry's avatar
      Detect underflow in fromIntegral/Int->Natural rule · a820f900
      Sylvain Henry authored and Marge Bot's avatar Marge Bot committed
      Fix #20066
      a820f900
    • Simon Peyton Jones's avatar
      One-shot changes (#20008) · 6ac9ea86
      Simon Peyton Jones authored and Marge Bot's avatar Marge Bot committed
      I discovered that GHC.Core.Unify.bindTv was getting arity 2,
      rather than 3, in one of my builds.  In HEAD it does get the right
      arity, but only because CallArity (just) manages to spot it. In my
      situation it (just) failed to discover this.
      
      Best to make it robust, which this patch does.  See
      Note [INLINE pragmas and (>>)] in GHC.Utils.Monad.
      
      There a bunch of other modules that probably should have the same
      treatment:
        GHC.CmmToAsm.Reg.Linear.State
        GHC.Tc.Solver.Monad
        GHC.Tc.Solver.Rewrite
        GHC.Utils.Monad.State.Lazy
        GHC.Utils.Monad.State.Strict
      but doing so is not part of this patch
      6ac9ea86
  2. Jul 01, 2021
  3. Jun 29, 2021
    • Matthew Pickering's avatar
      ci: Don't allow aarch64-darwin to fail · 2ce7c515
      Matthew Pickering authored and Marge Bot's avatar Marge Bot committed
      Part way to #20013
      2ce7c515
    • sheaf's avatar
      Use HsExpansion for overloaded list patterns · 4e9f58c7
      sheaf authored and Marge Bot's avatar Marge Bot committed
      Fixes #14380, #19997
      4e9f58c7
    • Sebastian Graf's avatar
      Demand: Better representation (#19050) · b760c1f7
      Sebastian Graf authored and Marge Bot's avatar Marge Bot committed
      In #19050, we identified several ways in which we could make more illegal
      states irrepresentable. This patch introduces a few representation changes
      around `Demand` and `Card` with a better and earlier-failing API exported
      through pattern synonyms. Specifically,
      
      1. The old enum definition of `Card` led to severely bloated code of operations
         on it. I switched to a bit vector representation; much nicer overall IMO.
         See Note [Bit vector representation for Card].
      
      Most of the gripes with the old representation were related to where which kind
      of `Card` was allowed and the fact that it doesn't make sense for an absent or
      bottoming demand to carry a `SubDemand` that describes an evaluation context
      that is never realised.
      
      2. So I refactored the `Demand` representation so that it has two new data
         constructors for `AbsDmd` and `BotDmd`. The old `(:*)` data constructor
         becomes a pattern synonym which expands absent demands as needed, so that
         it still forms a complete match and a versatile builder. The new `Demand`
         data constructor now carries a `CardNonAbs` and only occurs in a very limited
         number of internal call sites.
      3. Wherever a full-blown `Card` might end up in a `CardNonAbs` field (like that
         of `D` or `Call`), I assert the consistency. When the smart builder of `(:*)`
         is called with an absent `Card`, I assert that the `SubDemand` is the same
         that we would expand to in the matcher.
      4. `Poly` now takes a `CardNonOnce` and encodes the previously noticed invariant
         that we never produce `Poly C_11` or `Poly C_01`. I made sure that we never
         construct a `Poly` with `C_11` or `C_01`.
      
      Fixes #19050.
      
      We lose a tiny bit of anal perf overall, probably because the new `Demand`
      definition can't be unboxed. The biggest loser is WWRec, where allocations go
      from 16MB to 26MB in DmdAnal, making up for a total increase of (merely) 1.6%.
      It's all within acceptance thresholds.
      There are even two ghc/alloc metric decreases. T11545 decreases by *67%*!
      
      Metric Decrease:
          T11545
          T18304
      b760c1f7
  4. Jun 28, 2021
  5. Jun 27, 2021
    • Matthew Pickering's avatar
      Revert "Make reallyUnsafePtrEquality# levity-polymorphic" · 469126b3
      Matthew Pickering authored and Marge Bot's avatar Marge Bot committed
      This reverts commit d1f59540.
      
      This commit breaks the build of unordered-containers
      
      ```
      [3 of 9] Compiling Data.HashMap.Internal.Array ( Data/HashMap/Internal/Array.hs, dist/build/Data/HashMap/Internal/Array.o, dist/build/Data/HashMap/Internal/Array.dyn_o )
      *** Parser [Data.HashMap.Internal.Array]:
      Parser [Data.HashMap.Internal.Array]: alloc=21043544 time=13.621
      *** Renamer/typechecker [Data.HashMap.Internal.Array]:
      Renamer/typechecker [Data.HashMap.Internal.Array]: alloc=151218672 time=187.083
      *** Desugar [Data.HashMap.Internal.Array]:
      ghc: panic! (the 'impossible' happened)
        GHC version 9.3.20210625:
      	expectJust splitFunTy
      CallStack (from HasCallStack):
        error, called at compiler/GHC/Data/Maybe.hs:68:27 in ghc:GHC.Data.Maybe
        expectJust, called at compiler/GHC/Core/Type.hs:1247:14 in ghc:GHC.Core.Type
      ```
      
      Revert containers submodule update
      469126b3
    • Sebastian Graf's avatar
      testsuite: Widen acceptance window of T12545 (#19414) · 43bbf4b2
      Sebastian Graf authored and Marge Bot's avatar Marge Bot committed
      In a sequel of #19414, I wrote a script that measures min and max allocation
      bounds of T12545 based on randomly modifying -dunique-increment. I got a spread
      of as much as 4.8%. But instead of widening the acceptance window further (to
      5%), I committed the script as part of this commit, so that false positive
      increases can easily be diagnosed by comparing min and max bounds to HEAD.
      
      Indeed, for !5814 we have seen T12545 go from -0.3% to 3.3% after a rebase.
      I made sure that the min and max bounds actually stayed the same.
      In the future, this kind of check can very easily be done in a matter of a
      minute. Maybe we should increase the acceptance threshold if we need to check
      often (leave a comment on #19414 if you had to check), but I've not been bitten
      by it for half a year, which seems OK.
      
      Metric Increase:
          T12545
      43bbf4b2
    • Sebastian Graf's avatar
      Inliner: Regard LitRubbish as TrivArg and not ConLike · b92479f9
      Sebastian Graf authored and Marge Bot's avatar Marge Bot committed
      Part of fixing #19766 required the emission of `LitRubbish` as absent filler in
      places where we used `absentError` before. In WWRec we have the situation that
      such bindings occur in the argument to functions. With `LitRubbish` we inlined
      those functions, because
      
       1. The absent binding was regarded as ConLike. So I fixed `exprIsHNFLike` to
          respond `False` to `LitRubbish`.
       2. The other source of inlining was that after inlining such an absent
          binding, `LitRubbish` itself was regarded `ValueArg` by `interestingArg`,
          leading to more inlining. It now responds `TrivArg` to `LitRubbish`.
      
      Fixes #20035.
      
      There's one slight 1.6% ghc/alloc regression left in T15164 that is due to an
      additional specialisation `$s$cget`. I've no idea why that happens; the Core
      output before is identical and has the call site that we specialise for.
      
      Metric Decrease:
          WWRec
      b92479f9
    • Sebastian Graf's avatar
      Add regression test for #17819 · e69d070b
      Sebastian Graf authored and Marge Bot's avatar Marge Bot committed
      The only item left in #17819. Fixes #17819.
      e69d070b
    • Sebastian Graf's avatar
      WorkWrap: Make mkWWstr and mkWWcpr generate fewer let bindings · 37472a10
      Sebastian Graf authored and Marge Bot's avatar Marge Bot committed
      In !5814 (comment 355144),
      Simon noted that `mkWWstr` and `mkWWcpr` could generate fewer let bindings and
      be implemented less indirectly by returning the rebuilt expressions directly, e.g. instead of
      
      ```
      f :: (Int, Int) -> Int
      f (x, y) = x+y
      
      ==>
      
      f :: (Int, Int) -> Int
      f p = case p of (x, y) ->
            case x of I# x' ->
            case y of I# y' ->
            case $wf x' y' of r' ->
            let r = I# r' -- immediately returned
            in r
      
      f :: Int# -> Int# -> Int#
      $wf x' y' = let x = I# x' in   -- only used in p
                  let y = I# y' in   -- only used in p
                  let p = (x, y) in  -- only used in the App below
                  case (\(x,y) -> x+y) p of I# r' ->
                  r'
      ```
      
      we know generate
      
      ```
      f :: (Int, Int) -> Int
      f p = case p of (x, y) ->
            case x of I# x' ->
            case y of I# y' ->
            case $wf x' y' of r' ->
            I# r' -- 1 fewer let
      
      f :: Int# -> Int# -> Int#
      $wf x' y' = case (\(x,y) -> x+y) (I# x, I# y) of I# r' -> -- 3 fewer lets
                  r'
      ```
      
      Which is much nicer and makes it easier to comprehend the output of
      worker-wrapper pre-Simplification as well as puts less strain on the Simplifier.
      
      I had to drop support for #18983, but we found that it's broken anyway.
      Simon is working on a patch that provides a bit more justification.
      37472a10
    • Sebastian Graf's avatar
      WorkWrap: Remove mkWWargs (#19874) · eee498bf
      Sebastian Graf authored and Marge Bot's avatar Marge Bot committed
      `mkWWargs`'s job was pushing casts inwards and doing eta expansion to match
      the arity with the number of argument demands we w/w for.
      
      Nowadays, we use the Simplifier to eta expand to arity. In fact, in recent years
      we have even seen the eta expansion done by w/w as harmful, see Note [Don't eta
      expand in w/w]. If a function hasn't enough manifest lambdas, don't w/w it!
      
      What purpose does `mkWWargs` serve in this world? Not a great one, it turns out!
      I could remove it by pulling some important bits,
      notably Note [Freshen WW arguments] and Note [Join points and beta-redexes].
      Result: We reuse the freshened binder names of the wrapper in the
      worker where possible (see testuite changes), much nicer!
      
      In order to avoid scoping errors due to lambda-bound unfoldings in worker
      arguments, we zap those unfoldings now. In doing so, we fix #19766.
      
      Fixes #19874.
      eee498bf
    • Sebastian Graf's avatar
      Simplifier: Do Cast W/W for INLINE strong loop-breakers · d7758da4
      Sebastian Graf authored and Marge Bot's avatar Marge Bot committed
      Strong loop-breakers never inline, INLINE pragma or not.
      Hence they should be treated as if there was no INLINE pragma on them.
      
      Also not doing Cast W/W for INLINE strong loop-breakers will trip up Strictness
      W/W, because it treats them as if there was no INLINE pragma. Subsequently,
      that will lead to a panic once Strictness W/W will no longer do eta-expansion,
      as we discovered while implementing !5814.
      
      I also renamed to `unfoldingInfo` to `realUnfoldingInfo` and redefined
      `unfoldingInfo` to zap the unfolding it returns in case of a strong loop-breaker.
      Now the naming and semantics is symmetrical to `idUnfolding`/`realIdUnfolding`.
      
      Now there was no more reason for `hasInlineUnfolding` to operate on `Id`,
      because the zapping of strong loop-breaker unfoldings moved from `idUnfolding`
      to `unfoldingInfo`, so I refactored it to take `IdInfo` and call it both from
      the Simplifier and WorkWrap, making it utterly clear that both checks are
      equivalent.
      d7758da4
    • Jakob Brünker's avatar
      Tc: Allow Typeable in quantified constraints · 3e71874b
      Jakob Brünker authored and Marge Bot's avatar Marge Bot committed
      Previously, when using Typeable in a quantified constraint, GHC would
      complain that user-specified instances of Typeable aren't allowed. This
      was because checking for SigmaCtxt was missing from a check for whether
      an instance head is a hand-written binding.
      
      Fixes #20033
      3e71874b
    • Zubin's avatar
      user-guide: Improve documentation of NumDecimals · b1792fef
      Zubin authored and Marge Bot's avatar Marge Bot committed
      b1792fef
    • sheaf's avatar
      Re-export UnliftedRep and UnliftedType from GHC.Exts · 9b776cbb
      sheaf authored and Marge Bot's avatar Marge Bot committed
      9b776cbb
    • GHC GitLab CI's avatar
      rts: Eliminate redundant branch · 30f233fe
      GHC GitLab CI authored and Marge Bot's avatar Marge Bot committed
      Previously we branched unnecessarily on
      IF_NONMOVING_WRITE_BARRIER_ENABLED on every trip through the array
      barrier push loop.
      30f233fe
    • GHC GitLab CI's avatar
      codeGen: Fix header size for array write barriers · 221a104f
      GHC GitLab CI authored and Marge Bot's avatar Marge Bot committed
      Previously the code generator's logic for invoking the nonmoving write
      barrier was inconsistent with the write barrier itself. Namely, the code
      generator treated the header size argument as being in words whereas the
      barrier expected bytes. This was the cause of #19715.
      
      Fixes #19715.
      221a104f
  6. Jun 25, 2021
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