June 2013 - ghc-tickets

Re: [GHC] #703: all binaries built by ghc have executable stacks
by GHC 12 Jun '13

12 Jun '13

#703: all binaries built by ghc have executable stacks ---------------------------+------------------------------------------------ Reporter: duncan | Owner: Type: merge | Status: new Priority: normal | Milestone: 6.6.1 Component: Compiler | Version: 7.4.2 Resolution: | Keywords: Os: Linux | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Moderate (less than a day) Testcase: N/A | Blockedby: Blocking: | Related: ---------------------------+------------------------------------------------ Changes (by fpishard): * status: closed => new * cc: fpishard (added) * component: Compiler (NCG) => Compiler * failure: => None/Unknown * version: 6.4.1 => 7.4.2 * owner: igloo => * resolution: fixed => -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/703#comment:10> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #7977: Optimization: Shift dropped list heads by coeffecient to prevent thunk generation
by GHC 11 Jun '13

11 Jun '13

#7977: Optimization: Shift dropped list heads by coeffecient to prevent thunk generation -----------------------------+---------------------------------------------- Reporter: schyler | Owner: Type: feature request | Status: new Priority: normal | Component: Compiler Version: 7.4.2 | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Blockedby: Blocking: | Related: -----------------------------+---------------------------------------------- Consider the following snippet(s) equivalent to ([a..b] !! n), the source of (!!) and the source of drop: {{{ normal_list :: Int -> Int normal_list n = head $ drop n [a..b] shifted_list :: Int -> Int shifted_list n = head $ drop (n-n) [(a+n)..b] }}} {{{ xs !! n | n < 0 = undefined [] !! _ = undefined (x:_) !! 0 = x (_:xs) !! n = xs !! (n-1) }}} {{{ drop n xs | n <= 0 = xs drop _ [] = [] drop n (_:xs) = drop (n-1) xs }}} Notice the (_:xs) matching in these functions as a result of WHNF. In the first case, normal_list, thunks are generated for x in ({-x-}_:xs) of the target list and overhead is seen in the pattern matching/guard of n in drop. In the second case, shifted_list, this overhead can be completely removed by adding a coefficient such that the list starts at the programmatically defined lower bound, a, plus the known fact that the head is dropped n times. Hence, given the example above, consider: {{{ [x * x + 3 | x <- [1..]] !! n -- versus [x * x + 3 | x <- [(1+n)..]] !! (n-n) -- which is optimized into [x * x + 3 | x <- [(n+1)..]] !! 0 -- which is effectively head [x * x + 3 | x <- [(n+1)..]] }}} The operation is turned from O(n) into O(1). Consider benchmark proving GHC 7.4.2 does not make this optimization under -O2: {{{ import Criterion.Main normal_list :: Int -> Int normal_list n = head $ drop n [1..] shifted_list :: Int -> Int shifted_list n = head $ drop (n-n) [(1+n)..] main = defaultMain [ bench "normal_list 1000" $ whnf normal_list 1000 , bench "shifted_list 1000" $ whnf shifted_list 1000 ] }}} {{{ C:\Users\Kyle\Desktop>ghc -O2 listco.hs [1 of 1] Compiling Main ( listco.hs, listco.o ) Linking listco.exe ... C:\Users\Kyle\Desktop>listco.exe warming up estimating clock resolution... mean is 4.644044 us (160001 iterations) found 319255 outliers among 159999 samples (199.5%) 159256 (99.5%) low severe 159999 (100.0%) high severe estimating cost of a clock call... mean is 310.3118 ns (34 iterations) benchmarking normal_list 1000 Warning: Couldn't open /dev/urandom Warning: using system clock for seed instead (quality will be lower) mean: 7.352463 us, lb 7.058339 us, ub 7.646574 us, ci 0.950 std dev: 1.478087 us, lb 1.478066 us, ub 1.478200 us, ci 0.950 variance introduced by outliers: 94.651% variance is severely inflated by outliers benchmarking shifted_list 1000 mean: 46.42819 ns, lb 45.44244 ns, ub 47.21689 ns, ci 0.950 std dev: 4.495757 ns, lb 4.035428 ns, ub 4.832396 ns, ci 0.950 variance introduced by outliers: 77.960% variance is severely inflated by outliers }}} -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7977> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #6135: Unboxed Booleans
by GHC 11 Jun '13

11 Jun '13

#6135: Unboxed Booleans -------------------------------+-------------------------------------------- Reporter: benl | Owner: jstolarek Type: feature request | Status: patch Priority: normal | Milestone: 7.8.1 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: | Blockedby: Blocking: | Related: #605 -------------------------------+-------------------------------------------- Comment(by gregorycollins): It's the {{{setge %cl}}} instruction in the code snippet on that wiki page, which: {{{ Sets the byte in the operand to 1 if the Sign Flag equals the Overflow Flag, otherwise sets the operand to 0. }}} (see e.g. http://web.itu.edu.tr/kesgin/mul06/intel/instr/setge_setnl.html) Or one of the other {{{SETcc}}} functions. This instruction doesn't branch, so the generated code pipelines better. -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6135#comment:70> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #6135: Unboxed Booleans
by GHC 11 Jun '13

11 Jun '13

#6135: Unboxed Booleans -------------------------------+-------------------------------------------- Reporter: benl | Owner: jstolarek Type: feature request | Status: patch Priority: normal | Milestone: 7.8.1 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: | Blockedby: Blocking: | Related: #605 -------------------------------+-------------------------------------------- Comment(by simonpj): I think we should treat all Bool-returning primops identically. I think it's just the `sameX` family of operators, and they can perfectly well return `Int#` in the same way that `eqInt#` now does. Then you can eliminate those cases from the codegen path, which is great. One thing I'm puzzled about is this. If `>#` yields an `Int#`, how does that `Int#` get into a register? Do we get code like {{{ cmp x,y bne L1 ld R1, 1 goto L2 L1: ld R1, 0 L2: ...now R1 has the Int#... }}} Getting the info from the status flags into a value, which we then compare with 0, would be silly. How is this avoided? Esp when there are several tests and you do logical operations on the `Int#`? I looked on the wiki page http://hackage.haskell.org/trac/ghc/wiki/PrimBool, but could not figure it out. Maybe worth adding a section to explain this? Thanks Simon Simon -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6135#comment:69> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7272: PolyKinds and mutually recursive modules
by GHC 11 Jun '13

11 Jun '13

#7272: PolyKinds and mutually recursive modules -------------------------------+-------------------------------------------- Reporter: dreixel | Owner: Type: bug | Status: closed Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.6.1 Resolution: fixed | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: polykinds/T7272 | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- Changes (by simonpj): * status: new => closed * resolution: => fixed Comment: Maybe now I have finally done it :-) -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7272#comment:12> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7272: PolyKinds and mutually recursive modules
by GHC 11 Jun '13

11 Jun '13

#7272: PolyKinds and mutually recursive modules -------------------------------+-------------------------------------------- Reporter: dreixel | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: polykinds/T7272 | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- Comment(by simonpj@…): commit 6ecfa98d7b9860ccf29359d0bb3d6fda1d7c7335 {{{ Author: Simon Peyton Jones <simonpj(a)microsoft.com> Date: Tue Jun 11 09:49:20 2013 +0100 Actually make the change described in 'Fix egregious typo in cmpTypeX' I reverted it to try something else and forgot to put it back! Fixes Trac #7272 (again!). compiler/types/Kind.lhs | 30 ++++++++++++++---------------- compiler/types/Type.lhs | 14 ++++++-------- 2 files changed, 20 insertions(+), 24 deletions(-) }}} -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7272#comment:11> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #7975: "impossible" failure while type checking
by GHC 11 Jun '13

11 Jun '13

#7975: "impossible" failure while type checking -------------------------------+-------------------------------------------- Reporter: jonnadal | Owner: Type: bug | Status: new Priority: normal | Component: Compiler (Type checker) Version: 7.6.3 | Keywords: Os: MacOS X | Architecture: x86 Failure: Compile-time crash | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- $ cat failure.hs {{{ import Control.Monad.Trans.Class oops :: () -> IO () -> IO () oops = lift . lift main = return () }}} $ ghc failure.hs {{{ [1 of 1] Compiling Main ( failure.hs, failure.o ) failure.hs:3:8:ghc: panic! (the 'impossible' happened) (GHC version 7.6.3 for i386-apple-darwin): kindFunResult ghc-prim:GHC.Prim.*{(w) tc 34d} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7975> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7272: PolyKinds and mutually recursive modules
by GHC 11 Jun '13

11 Jun '13

#7272: PolyKinds and mutually recursive modules -------------------------------+-------------------------------------------- Reporter: dreixel | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: polykinds/T7272 | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- Comment(by simonpj): Crumbs. To err once might be carelessness, but twice? I switched off the change to investigate something else and forgot to switch it on again. Simon -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7272#comment:10> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7272: PolyKinds and mutually recursive modules
by GHC 10 Jun '13

10 Jun '13

#7272: PolyKinds and mutually recursive modules -------------------------------+-------------------------------------------- Reporter: dreixel | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: polykinds/T7272 | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- Changes (by monoidal): * owner: dreixel => * status: closed => new * resolution: fixed => Comment: Simon: The commit did not fix the typo. -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7272#comment:9> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7272: PolyKinds and mutually recursive modules
by GHC 10 Jun '13

10 Jun '13

#7272: PolyKinds and mutually recursive modules -------------------------------+-------------------------------------------- Reporter: dreixel | Owner: dreixel Type: bug | Status: closed Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.6.1 Resolution: fixed | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: polykinds/T7272 | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- Comment(by simonpj): Thanks for pointing this out! -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7272#comment:8> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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