January 2014 - ghc-tickets

Re: [GHC] #5916: runST isn't free
by GHC 08 Jan '14

08 Jan '14

#5916: runST isn't free -------------------------------------+------------------------------------ Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by nomeata): Turns out I spoke too soon (and that the test suite really does not cover this): This code {{{ #!haskell main = let f () = runST $ do ref <- newSTRef 0 modifySTRef ref (+1) readSTRef ref in print (f () + f ()) }}} will be broken by my approach (output `3` instead of `2`), as there are no free variables that differing – obvious, now that I see it. Too bad, was hoping to produce something usable today... at least I’ll add a possibly useful testcase. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5916#comment:14> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5916: runST isn't free
by GHC 08 Jan '14

08 Jan '14

#5916: runST isn't free -------------------------------------+------------------------------------ Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by Joachim Breitner <mail@…>): In [changeset:"e17a62c14b6a1fce681b06ebd0cc11223841f92f/testsuite"]: {{{ #!CommitTicketReference repository="testsuite" revision="e17a62c14b6a1fce681b06ebd0cc11223841f92f" Test that runST is not inlined prematurely This resulted form a discussion about #5916. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5916#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #2786: Blackhole loops are not detected and reported in GHCi
by GHC 08 Jan '14

08 Jan '14

#2786: Blackhole loops are not detected and reported in GHCi -------------------------------------+------------------------------------ Reporter: simonmar | Owner: Type: bug | Status: new Priority: normal | Milestone: _|_ Component: GHCi | Version: 6.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Changes (by lelf): * cc: me@…, hvr (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2786#comment:5> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5916: runST isn't free
by GHC 08 Jan '14

08 Jan '14

#5916: runST isn't free -------------------------------------+------------------------------------ Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by nomeata): Using {{{#!haskell {-# INLINE runSTRep #-} runSTRep :: (forall s. STRep s a) -> a runSTRep st_rep = case st_rep (stWorld# st_rep) of (# _, r #) -> r {-# NOINLINE stWorld# #-} stWorld# :: a -> State# RealWorld stWorld# _ = realWorld# }}} it validates. But do we actually have a test for this? Here would be one: {{{#!haskell import Control.Monad.ST import Data.STRef main = let f n = runST $ do ref <- newSTRef 0 modifySTRef ref (+n) readSTRef ref in print (f 1 + f 2) }}} returns 3 in master, returns 4 if I inline `runSTRep`, and returns 3 with the `stWorld#`-trick. So unless someone says that this is not worth it (which would be strange, given that this bug is about an unexpected real-world performance issue), I suggest to give `runSTRep` a custom unfolding in `MkId` that replaces `runSTRep e` by `case e (stWorld# $(all free local variables of e)) of (# _, r #) -> r`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5916#comment:12> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7942: aarch64 support in ghc
by GHC 08 Jan '14

08 Jan '14

#7942: aarch64 support in ghc --------------------------------------------+--------------------------- Reporter: jcapik | Owner: kgardas Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Linux | Architecture: arm Type of failure: GHC doesn't work at all | Difficulty: Unknown Test Case: | Blocked By: 7623 Blocking: | Related Tickets: --------------------------------------------+--------------------------- Comment (by carter): sounds reasonable. Will the arm 32 bit ghc calling convention make sense for AArch64? We may need to get a patch into llvm before having a distinct aarch64 abi. (and we shoudl probably do some pretty thorough benchmarking before picking any such ABI) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7942#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3373: GHC API is not thread safe
by GHC 08 Jan '14

08 Jan '14

#3373: GHC API is not thread safe -------------------------------------+------------------------------------ Reporter: jcpetruzza | Owner: Type: feature request | Status: new Priority: low | Milestone: 7.10.1 Component: GHC API | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Changes (by lelf): * cc: me@… (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3373#comment:9> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5916: runST isn't free
by GHC 08 Jan '14

08 Jan '14

#5916: runST isn't free -------------------------------------+------------------------------------ Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by nomeata): Just noting down some idée fixe: The reason we are not inlining `runSTRep` is that we don’t want to expressions using the `realWorld#` token to become shared, right? How about `runSTRep` gets a special inlining that mentions all free variables of its argument, using a special token of type `stWorld# :: a -> RealWorld#`. So `runSTRep (f x (z x))` would get unfolded to {{{ case f x (z x) (stWorld# (f,x,z)) of (# _, r #) -> r }}} The variables mentioned in `stWorld’s` argument prevent this from being floated out, and I believe it ouldn’t that solve tibbe’s problem, right? It might also enable more CPR-related optimizations. When generating `STG`, the argument of `stWorld#` would of course be ignored. (In fact, it seems it would be correct ot have `runSTRep e = case e (stWorld# e) of (# _, #r) -> r`, which could be formulated as a plain `RULE`, but that would blow up the core expressions during compilation too much, I’d expect.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5916#comment:11> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1600: Optimisation: CPR the results of IO
by GHC 08 Jan '14

08 Jan '14

#1600: Optimisation: CPR the results of IO -------------------------------------+------------------------------------- Reporter: simonmar | Owner: nomeata Type: task | Status: new Priority: lowest | Milestone: 7.6.2 Component: Compiler | Version: 6.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: Runtime | Difficulty: Moderate (less performance bug | than a day) Test Case: | Blocked By: Blocking: | Related Tickets: #8598 -------------------------------------+------------------------------------- Comment (by nomeata): (Update to sidenote: inlining `runSTRep` may allow it to get a `CPR` property, but this does not magically help with join-points, also see [wiki:NestedCPR/wave4main]). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1600#comment:35> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7679: Regression in -fregs-graph performance
by GHC 08 Jan '14

08 Jan '14

#7679: Regression in -fregs-graph performance --------------------------------------------+------------------------------ Reporter: simonmar | Owner: Type: bug | Status: new Priority: high | Milestone: 7.8.1 Component: Compiler (NCG) | Version: 7.6.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime performance bug | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: #7192, | #8657 --------------------------------------------+------------------------------ Changes (by simonmar): * cc: simonmar (added) * related: #7192 => #7192, #8657 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7679#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7942: aarch64 support in ghc
by GHC 08 Jan '14

08 Jan '14

#7942: aarch64 support in ghc --------------------------------------------+--------------------------- Reporter: jcapik | Owner: kgardas Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Linux | Architecture: arm Type of failure: GHC doesn't work at all | Difficulty: Unknown Test Case: | Blocked By: 7623 Blocking: | Related Tickets: --------------------------------------------+--------------------------- Comment (by kgardas): I'm following the same way like Stephen/David/me did ARM in the past: https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/Backends/LLVM/GHC… NCG way makes sense once you do have LLVM working, then you can try -fasm on smallest examples and do it step-by-step with increased example complexity. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7942#comment:12> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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