August 2016 - ghc-tickets

[GHC] #11598: Cache coercion kinds and roles
by GHC 21 Dec '16

21 Dec '16

#11598: Cache coercion kinds and roles -------------------------------------+------------------------------------- Reporter: goldfire | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- Because we never inspect the structure of a coercion, it is easy to cache coercions' kinds and role at the top level, using something like this: {{{ data Coercion = MkCoercion { coercionKind :: Pair Type , coercionRole :: Role , coercionRep :: CoercionRep } data CoercionRep = -- the long, recursive datatype we have now }}} In the process, various role and type information currently stored in the recursive structure could be dropped. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11598> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12444: Regression: panic! on inaccessible code with constraint
by GHC 21 Dec '16

21 Dec '16

#12444: Regression: panic! on inaccessible code with constraint -------------------------------------+------------------------------------- Reporter: zilinc | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Running the following program with ghci-8.0.1: {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} module Prove where data Nat = Zero | Succ Nat data SNat (n :: Nat) where SZero :: SNat Zero SSucc :: SNat n -> SNat (Succ n) type family (:+:) (a :: Nat) (b :: Nat) :: Nat where m :+: Zero = m m :+: (Succ n) = Succ (m :+: n) sadd :: ((Succ n1 :+: n) ~ Succ (n1 :+: n), (Succ n1) ~ m) => SNat m -> SNat n -> SNat (m :+: n) sadd SZero n = n }}} -ddump-tc-trace shows: {{{ ... dischargeFmv s_a9qV[fuv:4] = t_a9qW[tau:5] (1 kicked out) doTopReactFunEq (occurs) old_ev: [D] _ :: ((n1_a9qu[sk] :+: 'Succ s_a9qV[fuv:4]) :: Nat) GHC.Prim.~# (s_a9qV[fuv:4] :: Nat)ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): ctEvCoercion [D] _ :: (t_a9qW[tau:5] :: Nat) ~# ('Succ (n1_a9qu[sk] :+: s_a9qV[fuv:4]) :: Nat) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} It is rightly rejected by ghci-7.10.2: {{{ Prove.hs:42:6: Couldn't match type ‘'Succ n1’ with ‘'Zero’ Inaccessible code in a pattern with constructor SZero :: SNat 'Zero, in an equation for ‘sadd’ In the pattern: SZero In an equation for ‘sadd’: sadd SZero n = n Failed, modules loaded: none. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12444> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11522: maxStkSize can overflow
by GHC 19 Dec '16

19 Dec '16

#11522: maxStkSize can overflow -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Runtime | Version: 7.8.4 System | 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 `maxStkSize` field of `GC_FLAGS` is a `nat`, or `unsigned int`. It's measured in words, but still 32G is not an unreasonable amount of memory by today's standards. Maybe it's unlikely that anyone would want to set the stack size limit to more than 32G. But if you happen to have just over 40G of physical memory then the default stack size limit will overflow to a value just above zero and then Bad Things would happen. If we want to actually enforce stack limits that are greater than 2^32^ words, we would need to increase the size of the `tot_stack_size` field of a TSO also. Simple test of overflow behavior: `ghci +RTS -K32.0001G` will exit with a stack overflow. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11522> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11502: Scrutinize use of 'long' in rts/
by GHC 19 Dec '16

19 Dec '16

#11502: Scrutinize use of 'long' in rts/ -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Runtime | Version: 7.10.3 System | 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: -------------------------------------+------------------------------------- In commit 53055bb5023e8cc145ad8a9cd36ac56cee4695b0 (#5656), several uses of `int` in the rts were replaced by `long`, to avoid potential overflows for some calculations. On Windows though, `int` and `long` have the same size (4 bytes). Carefully go through all uses of `long` in `rts/`, and replace by one of the types from `includes/stg/Types.h`: * `long` -> `StgInt` or `StgInt64` * `unsigned long` -> `StgWord` or `StgWord64` -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11502> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10007: Fix misattribution of Cost Centre profiles to lintAnnots
by GHC 19 Dec '16

19 Dec '16

#10007: Fix misattribution of Cost Centre profiles to lintAnnots -------------------------------------+------------------------------------- Reporter: | Owner: scpmw thoughtpolice | Status: new Type: bug | Milestone: 7.10.1 Priority: high | Version: 7.10.1-rc1 Component: Profiling | Operating System: Unknown/Multiple Keywords: | Type of failure: Incorrect result Architecture: | at runtime Unknown/Multiple | Blocked By: Test Case: | Related Tickets: #9961 Blocking: | Differential Revisions: Phab:D616 | -------------------------------------+------------------------------------- Split off from #9961 - the profiling results while debugging erroneously reported that most cost centre profiles were a result of `lintAnnots`, as opposed to `CSE`. This is a bug. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10007> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10723: Make declarations in signatures "weakly bound" until they are used
by GHC 17 Dec '16

17 Dec '16

#10723: Make declarations in signatures "weakly bound" until they are used -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: feature | Status: new request | Priority: normal | Milestone: Component: Package | Version: 7.11 system | Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Suppose you are the author of a library in a Backpack world, and you publish a signature package which defines the entire public facing interface of your library. The library `foo` which uses of your library decides to `include` the signature package for convenience, but actually only uses a small portion of the API. Later, you make a BC-breaking change in one part of the library and release a new signature package. The library `bar` which uses your library includes this NEW signature package, using a different portion of the API which was unaffected by the by the BC change. Now, a hapless user tries to use `foo` and `bar`, but Backpack complains that the requirements are not compatible. What's the problem here? The practice of writing reusable signature packages for people to use caused the requirements of `foo` and `bar` to become too large, since they included a lot of junk that these libraries didn't actually use. It would be far better if you could `include` a signature package, but only "require" the bits of it that you actually used! How can we achieve this? 1. We augment the `ModIface` of signature merges (#10690) to record whether or not a declaration was (transitively) used or not by some module. Used declarations must be filled, but unused ones are treated more flexibly: if they are merged with a different, incompatible but used requirement, they disappear, and we don't check if an implementing module actually implemented the declaration. (If two unused incompatible requirements are merged, we just erase the name.) 2. How do we compute the usage info? I think it will have to be done during shaping (which runs the renamer). We only need to annotate each declaration a signature with the transitive set of names from other signatures that it has used--this can be incrementally computed. (It's not necessary to annotate declarations in modules, since they are always assumed to use holes). Then whenever a declaration from a signature is used in a module, we mark its transitive set as used. This information can then be used later when constructing the merged `ModIface` which represents the "public requirement" of the package. So, for example, a package containing only signatures would contain all unused declarations (however, they may start being used by a package which includes them). Any unused declaration which isn't mixed with another incompatible declaration can be imported (causing it to be used), but we will complain if you try to use a name and we can't tell which declaration to use. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10723> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9601: Make the rewrite rule system more powerful
by GHC 16 Dec '16

16 Dec '16

#9601: Make the rewrite rule system more powerful -------------------------------------+------------------------------------- Reporter: spacekitteh | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Project (more | Type of failure: than a week) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- It would be amazing if the current RULES system could be upgraded to include various predicates, or even into a full-on strategic programming system. This would allow far far more optimisations to be possible, rather than the current conservative system where you have to make sure that the optimisations ALWAYS apply. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9601> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11784: panic "hscCmmFile: no_mod" with `-v2 and above
by GHC 16 Dec '16

16 Dec '16

#11784: panic "hscCmmFile: no_mod" with `-v2 and above -------------------------------------+------------------------------------- Reporter: erikd | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Initailly found this on powerpc when debugging #11773, but it also happens on x86_64. The command line: {{{ inplace/bin/ghc-stage1 -static -H64m -O0 -Wall -v2 -Iincludes \ -Iincludes/dist -Iincludes/dist-derivedconstants/header \ -Iincludes/dist-ghcconstants/header -Irts -Irts/dist/build \ -DCOMPILING_RTS -this-unit-id rts -optc-DNOSMP -dcmm-lint -i -irts \ -irts/dist/build -irts/dist/build/autogen -Irts/dist/build \ -Irts/dist/build/autogen -O2 -Wnoncanonical-monad-instances -c\ rts/StgStartup.cmm -o rts/dist/build/StgStartup.o }}} panics with a message: {{{ ghc-stage1: panic! (the 'impossible' happened) (GHC version 8.1.20160402 for powerpc-unknown-linux): hscCmmFile: no_mod }}} The only thing that was added to the command line that is different from the normal build command is the `-v2`. This is caused by the code (in compiler/main/HscMain.hs): {{{ no_mod = panic "hscCmmFile: no_mod" }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11784> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11221: Remove -fwarn-context-quantification
by GHC 16 Dec '16

16 Dec '16

#11221: Remove -fwarn-context-quantification -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: task | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- This option was deprecated and does nothing as of GHC 8.0. Remove `Opt_WarnContextQuantification` and its uses from `DynFlags`. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11221> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8299: Add richer data model address arithmetic: AddrDiff and AddrInt (ie d Int_ptr_diff and Int_ptr_size)
by GHC 15 Dec '16

15 Dec '16

#8299: Add richer data model address arithmetic: AddrDiff and AddrInt (ie d Int_ptr_diff and Int_ptr_size) ----------------------------------------------+---------------------------- Reporter: carter | Owner: Type: feature request | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Project (more than a week) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: 8287 ----------------------------------------------+---------------------------- currently GHC's internals and code gen don't provide a strong distinction between Ints as data, and Ints for pointer / address arithmetic. This also comes up as being problematical in a number of ways. 1. We wind up having many portability issues around Int and pointer / address sizes. 2. adds some inessential complexity / problems to adding new architectures to ghc. eg x32 ABI which has 32bit pointers and 64bit ints somewhat breaks current assumptions in the GHC primops (because arrays are indexed by a byte offset, and the valid range for those is determined by the ABI pointer size!) 3. this Ints and Ptrs confusion we currently have, also means we can't leverage the Integer support in SIMD registers that is in most modern CPUs! If we could have those two separated better, theres a lot of low leve optimizations we could do for Int/Word data that we currently cant do! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8299> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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