October 2018 - ghc-tickets

[GHC] #14461: Reuse free variable lists through nested closures
by GHC 21 Oct '18

21 Oct '18

#14461: Reuse free variable lists through nested closures -------------------------------------+------------------------------------- Reporter: tdammers | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: 7258 Differential Rev(s): | Wiki Page: NestedClosures -------------------------------------+------------------------------------- Consider [wiki:NestedClosures] and [ticket:7258]; essentially, deeply nested closures exhibit quadratic compiler performance due to the fact that when allocating registers, each nesting level will have the compiler unpack the entire parent closure and then re-pack the variables into the child closure. To solve this, check if the parent closure can be carried along wholesale, and pull variables from there so that the repackaging can be bypassed. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14461> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14971: Use appropriatly sized comparison instruction for small values.
by GHC 20 Oct '18

20 Oct '18

#14971: Use appropriatly sized comparison instruction for small values. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: (CodeGen) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- GHC currently defaults all comparisons originating from Cmm switch statements to 64bit on x64. This incurs a small overhead in instruction size. Fixing this manually gave a speedup of ~1,5% in microbenchmarks. In detail we generate Cmm of the form: {{{ _s8Dg::P64 = R1; _c8EF::P64 = _s8Dg::P64 & 7; switch [1 .. 2] _c8EF::P64 { case 1 : goto c8Ey; case 2 : goto c8EC; } }}} Which results in assembly like: {{{ andl $7,%ebx cmpq $1,%rbx }}} It's obvious that c8EF fits into a byte, but is sized up to 64 bits. Changing this would enable us to use cmpl instead of cmpq and save us a byte on each comparison. While this isn't major in my microbenchmarks it resultet in a speedup of ~1,5% for such constructs in inner loops. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14971> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15350: gcdExtInteger violates assertion
by GHC 20 Oct '18

20 Oct '18

#15350: gcdExtInteger violates assertion -------------------------------------+------------------------------------- Reporter: Bodigrim | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Core | Version: 8.4.3 Libraries | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime crash Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!haskell {-# LANGUAGE UnboxedTuples #-} import GHC.Integer.GMP.Internals main = let (# _, s #) = gcdExtInteger 2 (2^65 + 1) in print s }}} fails with {{{#!haskell Assertion failed: (sn <= mp_size_abs(xn)), function integer_gmp_gcdext, file libraries/integer-gmp/cbits/wrappers.c, line 316. Abort trap: 6 }}} It happens because `s = -2^64` and does not fit one-limbed `BigNat`. The implementation of `gcdExtInteger x y` (https://github.com/ghc/ghc/blob/master/libraries/integer- gmp/src/GHC/Integer/Type.hs#L1392) allocates for `s` a buffer, equal to size of `x` (one limb in our case), but according to GMP manual (https://gmplib.org/manual/Number-Theoretic-Functions.html#index- mpz_005fgcdext) it should be equal to size of `y` (two limbs in our case). Hopefully, the diff is simple enough for a PR on GitHub. Otherwise I'll be happy to prepare a patch for Phabricator. {{{#!diff - s@(MBN# s#) <- newBigNat# (absI# xn#) + s@(MBN# s#) <- newBigNat# (absI# yn#) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15350> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15785: Improve/complete the GHCi :doc command
by GHC 20 Oct '18

20 Oct '18

#15785: Improve/complete the GHCi :doc command -------------------------------------+------------------------------------- Reporter: sjakobi | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: GHCi | Version: 8.6.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The `:doc` command, so far implemented as a ''tech preview'', could be a lot nicer: * For a type constructor, it should also show the data constructors and their documentation * It should include documentation on function arguments. * For records it should include any docs on the fields. Overall I think it should work roughly like the `:info` command, but of course enhanced by the docstrings. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15785> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15784: :doc shouldn't report <has no documentation> for a data constructor when it can show docs for the type constructor of the same name and type
by GHC 20 Oct '18

20 Oct '18

#15784: :doc shouldn't report <has no documentation> for a data constructor when it can show docs for the type constructor of the same name and type -------------------------------------+------------------------------------- Reporter: sjakobi | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.6.1 Keywords: newcomer | Operating System: Unknown/Multiple Architecture: | Type of failure: Poor/confusing Unknown/Multiple | error message Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ λ import Data.Monoid λ :doc Sum <has no documentation> Monoid under addition. >>> getSum (Sum 1 <> Sum 2 <> mempty) 3 }}} I think it would be nicer if we could elide the `<has no documentation>` message for the `Sum` data constructor here. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15784> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15258: Implement CMOV support.
by GHC 20 Oct '18

20 Oct '18

#15258: Implement CMOV support. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: task | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: CodeGen | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15258> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14830: Use test instead of cmp for comparison against zero.
by GHC 20 Oct '18

20 Oct '18

#14830: Use test instead of cmp for comparison against zero. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: (none) Type: task | Status: new Priority: low | Milestone: Component: Compiler | Version: (NCG) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- For comparisons `test r, r` and `cmp r, $0` are interchangeable at least on x86. However using test leads to slightly smaller code. (Saves a byte per comparison). A good starting point is stmtToInstrs in compiler/nativeGen/X86/CodeGen starting with how CmmCondBranch is compiled to Instructions. From there it should be not too hard to track down the required changes. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14830> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15757: Coercion Variable Almost Devoid Checking in ForAllCo
by GHC 19 Oct '18

19 Oct '18

#15757: Coercion Variable Almost Devoid Checking in ForAllCo -------------------------------------+------------------------------------- Reporter: ningning | Owner: (none) Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #15497 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In [https://repository.brynmawr.edu/cgi/viewcontent.cgi?article=1074&context=co… Richard's thesis] Section 5.8.5.2, there is a restriction on where a coercion variable can appear in `ForAllCo` for the sake of consistency: the coercion variable can appear nowhere except in coherence coercions. Currently this restriction is missing in coercion quantification (see #15497). The goal of this ticket is to add the missing restriction. After discussion with Richard, we restate the restriction a little bit: the coercion variable can appear nowhere except in `GRefl` and `Refl`. Allowing it to appear in `Refl` should not break consistency. Notice that this also means `liftCoSubst` might fail when it lifts a `ForAllTy` over a coercion variable to a `ForAllCo`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15757> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15775: Interpreter is treating a comment character as an identifier character.
by GHC 19 Oct '18

19 Oct '18

#15775: Interpreter is treating a comment character as an identifier character. -------------------------------------+------------------------------------- Reporter: philderbeast | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When bringing dhall-lang up in a REPL I stumbled across a warning about a character in a haddock comment. Should the interpreter be treating a comment character as an identifier character? https://github.com/dhall-lang/dhall- haskell/issues/646#issuecomment-430776320 {{{#!hs {-# LANGUAGE CPP #-} data Expr s a -- | > Combine x y ~ x ∧ y = Combine (Expr s a) (Expr s a) }}} {{{ > stack runghc -- --interactive Intersect.hs Intersect.hs:13:29: error: warning: treating Unicode character <U+2227> as identifier character rather than as '^' symbol [-Wunicode-homoglyph] -- | > Combine x y ~ x ∧ y ^ | 13 | -- | > Combine x y ~ x ∧ y | ^ 1 warning generated. > stack runghc -- --version runghc 8.4.3 }}} There's a [https://github.com/BlockScope/unicode-homoglyph unicode- homoglyph] repo with the reproduction. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15775> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15234: WARNING in hptSomeThingsBelowUs when using a source plugin
by GHC 19 Oct '18

19 Oct '18

#15234: WARNING in hptSomeThingsBelowUs when using a source plugin -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple SourcePlugins, plugins | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When using a source plugin with a stage2 compiler built with the devel2 flavour, there are a fair few warnings about hptSomeThingsBelowUs. {{{ WARNING in hptSomeThingsBelowUs missing module CoercePlugin Probable cause: out-of-date interface files }}} I don't know if this just started happening or has been going on for a while. Is this warning cause for concern? Everything appears to work as expected despite this hiccup. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15234> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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