November 2017 - ghc-tickets

[GHC] #8279: bad alignment in code gen yields substantial perf issue
by GHC 29 Aug '18

29 Aug '18

#8279: bad alignment in code gen yields substantial perf issue ------------------------------+-------------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime performance bug Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ------------------------------+-------------------------------------------- independently, a number of folks have noticed that in various ways, GHC currently has quite a few different memory alignment related performance problems that can have >= 10% perf impact! Nicolas Frisby notes {{{ On my laptop, a program showed a consistent slowdown with -fdicts-strict I didn't find any obvious causes in the Core differences, so I turned to Intel's Performance Counter Monitor for measurements. After trying a few counters, I eventuall saw that there are about an order of magnitude more misaligned memory loads with -fdicts-strict than without, so I think that may be a significant part of the slowdown. I'm not sure if these are code or data reads. Can anyone suggest how to validate this hypothesis about misaligned reads? A subsequent commit has changed the behavior I was seeing, so I'm not interested in alternatives means to determine if -fdicts-strict is somehow at fault — I'm just asking specifically about data/code memory alignment in GHC and how to diagnose/experiment with it. }}} Reid Barton has independently noted {{{ so I did a nofib run with llvm libraries, ghc quickbuild so there's this really simple benchmark tak, https://github.com/ghc/nofib/blob/master/imaginary/tak/Main.hs it doesn't use any libraries at all in the main loop because the Ints all get unboxed but it's still 8% slower with quick-llvm (vs -fasm) weird right? [14:36:30] <carter> could you post the asm it generates for that function? [14:36:49] <rwbarton> well it's identical between the two versions <rwbarton> but they get linked at different offsets because some llvm sections are different sizes <rwbarton> if I add a 128-byte symbol to the .text section to move it to the same address... then the llvm libs version is just as fast <rwbarton> well, apparently 404000 is good and 403f70 is bad <rwbarton> I guess I can test other alignments easily enough <rwbarton> I imagine it wants to start on a cache line <rwbarton> but I don't know if it's just a coincidence that it worked with the ncg libraries <rwbarton> that it got a good location <rwbarton> for this program every 32-byte aligned address is 10+% faster than any merely 16-byte aligned address <rwbarton> and by alignment I mean alignment of the start of the Haskell code section <carter> haswell, sandybridge, ivy bridge, other? <rwbarton> dunno <rwbarton> I have similar results on Intel(R) Core(TM)2 Duo CPU T7300 @ 2.00GHz <rwbarton> and on Quad-Core AMD Opteron(tm) Processor 2374 HE <carter> ok <rwbarton> trying a patch now that aligns all *_entry symbols to 32 bytes }}} the key point in there is that on the tak benchmark, better alignment for the code made a 10% perf differnce on TAk on Core2 and opteron cpus! benjamin scarlet and Luite are speculating that this may be further induced by Tables next to code (TNC) accidentally creating bad alignment so theres cache line pollution / conflicts between the L1 Instruction- cache and data-caches. So one experiment would be to have the TNC transform pad after the table so the function entry point starts on the next cacheline? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8279> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11350: Allow visible type application in patterns
by GHC 28 Aug '18

28 Aug '18

#11350: Allow visible type application in patterns -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple TypeApplications PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Constructors (and pattern synonyms) when treated as expressions may be applied to types: {{{#!hs {-# LANGUAGE TypeApplications #-} Nothing :: Maybe a Nothing @() :: Maybe () pattern Pair :: a -> a -> (a, a) pattern Pair x y = (x, y) Pair :: a -> a -> (a, a) Pair @Int :: Int -> Int -> (Int, Int) }}} But using them in patterns won't parse: {{{#!hs -- parse error in pattern: @Int maybeToList :: Maybe Int -> [Int] maybeToList (Nothing @Int) = [] maybeToList (Just @Int x) = [x] -- parse error in pattern: @Int add :: (Int, Int) -> Int add (Pair @Int x y) = x + y }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11350> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14021: 8.2.1 deb8 bindist fails to install on Windows 10 WSL
by GHC 26 Aug '18

26 Aug '18

#14021: 8.2.1 deb8 bindist fails to install on Windows 10 WSL -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.2 Component: Build System | Version: 8.2.1 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: -------------------------------------+------------------------------------- In principle the GHC 8.2.1 bindist for Debian 8 should work fine on WSL. However, in practice it fails during `make install` with this error, {{{ }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14021> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8733: I/O manager causes unnecessary syscalls in send/recv loops
by GHC 26 Aug '18

26 Aug '18

#8733: I/O manager causes unnecessary syscalls in send/recv loops ------------------------------------+------------------------------------- Reporter: tibbe | Owner: simonmar Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 7.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Network applications often call send followed by recv, to send a message and then read an answer. This causes syscall traces like this one: {{{ recvfrom(13, ) -- Haskell thread A sendto(13, ) -- Haskell thread A recvfrom(13, ) = -1 EAGAIN -- Haskell thread A epoll_ctl(3, ) -- Haskell thread A (a job for the IO manager) recvfrom(14, ) -- Haskell thread B sendto(14, ) -- Haskell thread B recvfrom(14, ) = -1 EAGAIN -- Haskell thread B epoll_ctl(3, ) -- Haskell thread B (a job for the IO manager) }}} The recvfrom call always fails, as the response from the partner we're communicating with won't be available right after we send the request. We ought to consider descheduling the thread as soon as sending is "done". The hard part is to figure out when that is. See http://www.yesodweb.com/blog/2014/02/new-warp for a real world example. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8733> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14483: getExecutablePath from System.Environment in base should follow symlinks properly.
by GHC 25 Aug '18

25 Aug '18

#14483: getExecutablePath from System.Environment in base should follow symlinks properly. -------------------------------------+------------------------------------- Reporter: angerman | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.3 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: -------------------------------------+------------------------------------- During the implementation of relocation capabilities in GHC for linux and macOS it came to light, that windows (which has had this support for quite some time), uses a custom implementation of `getExecutablePath`. Ideally this logic should be moved into `base`. Phyx- noted in D4121 that this should be possible for 8.6, as at that point Win32 should be new enough to be usable in base for this. The result would be that the custom code in GHC (SysTools) and the older copy in GhcPkg of the same code can be unified with the linux and macOS CPP conditional branch. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14483> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14460: Can't decompose ghc.exe path
by GHC 25 Aug '18

25 Aug '18

#14460: Can't decompose ghc.exe path -------------------------------------+------------------------------------- Reporter: astert | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Windows Architecture: | Type of failure: GHC doesn't work Unknown/Multiple | at all Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I downloaded the haskell platform, but when I try to use ghci I get this message: ghc.exe: panic!(the 'impossible' happened) (GHC version 8.2.1 for x86_64-unknown-mingw32): can't decompose ghc.exe path: "H:\\Programs\\Haskell\\8.2.1\\bin\\ghc.exe" -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14460> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14064: Compiling problem on FreeBSD 11 ("failed in phase")
by GHC 25 Aug '18

25 Aug '18

#14064: Compiling problem on FreeBSD 11 ("failed in phase") -------------------------------------+------------------------------------- Reporter: ohho | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: FreeBSD Architecture: x86_64 | Type of failure: GHC doesn't work (amd64) | at all Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The scenario showed as below: {{{ # This is a FreeBSD Jail for testing $ freebsd-version 11.1-RELEASE $ pkg info # (related packages only) binutils-2.28,1 GNU binary tools gcc-ecj-4.5 Eclipse Java Compiler used to build GCC Java gcc5-5.4.0_2 GNU Compiler Collection 5 gmake-4.2.1_1 GNU version of 'make' utility gmp-6.1.2 Free library for arbitrary precision arithmetic libiconv-1.14_10 Character set conversion library libunistring-0.9.7 Unicode string library mpc-1.0.3 Library of complex numbers with arbitrarily high precision mpfr-3.1.5_1 Library for multiple-precision floating- point computations perl5-5.24.1_1 Practical Extraction and Report Language $ ls -l /usr/local/lib/lib{iconv,charset,gmp}.* -rw-r--r-- 1 root wheel 6864 Jul 13 09:10 /usr/local/lib/libcharset.a lrwxr-xr-x 1 root wheel 19 Jul 13 09:10 /usr/local/lib/libcharset.so -> libcharset.so.1.0.0 lrwxr-xr-x 1 root wheel 19 Jul 13 09:10 /usr/local/lib/libcharset.so.1 -> libcharset.so.1.0.0 -rw-r--r-- 1 root wheel 10733 Jul 13 09:10 /usr/local/lib/libcharset.so.1.0.0 -rw-r--r-- 1 root wheel 1252196 Jul 13 09:23 /usr/local/lib/libgmp.a lrwxr-xr-x 1 root wheel 16 Jul 13 09:23 /usr/local/lib/libgmp.so -> libgmp.so.10.3.2 lrwxr-xr-x 1 root wheel 16 Jul 13 09:23 /usr/local/lib/libgmp.so.10 -> libgmp.so.10.3.2 -rwxr-xr-x 1 root wheel 531728 Jul 13 09:23 /usr/local/lib/libgmp.so.10.3.2 -rw-r--r-- 1 root wheel 1110392 Jul 13 09:10 /usr/local/lib/libiconv.a lrwxr-xr-x 1 root wheel 17 Jul 13 09:10 /usr/local/lib/libiconv.so -> libiconv.so.2.5.1 lrwxr-xr-x 1 root wheel 17 Jul 13 09:10 /usr/local/lib/libiconv.so.2 -> libiconv.so.2.5.1 -rw-r--r-- 1 root wheel 1076449 Jul 13 09:10 /usr/local/lib/libiconv.so.2.5.1 # installed using # env CC=/usr/local/bin/gcc5 LDFLAGS='-Wl,-rpath=/usr/local/lib/gcc5' ./configure --prefix=/home/ghc $ /home/ghc/bin/ghc --numeric-version 8.2.1 $ cat /home/ghc/lib/ghc-8.2.1/settings [("GCC extra via C opts", " -fwrapv -fno-builtin"), ("C compiler command", "/usr/local/bin/gcc5"), ("C compiler flags", " -fno-stack-protector"), ("C compiler link flags", " -fuse-ld=gold"), ("C compiler supports -no-pie", "NO"), ("Haskell CPP command","/usr/local/bin/gcc5"), ("Haskell CPP flags","-E -undef -traditional"), ("ld command", "ld.gold"), ("ld flags", ""), ("ld supports compact unwind", "YES"), ("ld supports build-id", "YES"), ("ld supports filelist", "NO"), ("ld is GNU ld", "YES"), ("ar command", "/usr/local/bin/ar"), ("ar flags", "q"), ("ar supports at file", "YES"), ("touch command", "touch"), ("dllwrap command", "/bin/false"), ("windres command", "/bin/false"), ("libtool command", "libtool"), ("perl command", "/usr/local/bin/perl"), ("cross compiling", "NO"), ("target os", "OSFreeBSD"), ("target arch", "ArchX86_64"), ("target word size", "8"), ("target has GNU nonexec stack", "True"), ("target has .ident directive", "True"), ("target has subsections via symbols", "False"), ("target has RTS linker", "@HaskellHaveRTSLinker@"), ("Unregisterised", "NO"), ("LLVM llc command", "llc"), ("LLVM opt command", "opt") ] $ /home/ghc/bin/ghci GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Prelude> (!!6) $ scanl (*) 1 [1..] 720 $ cat Main.hs module Main (main) where main :: IO () main = putStrLn "hello world" $ /home/ghc/bin/ghc -O0 --make Main.hs [1 of 1] Compiling Main ( Main.hs, Main.o ) Linking Main ... In file included from /home/ghc/lib/ghc-8.2.1/include/rts/Threads.h:19:0: error: 0, from /home/ghc/lib/ghc-8.2.1/include/Rts.h:173, from /tmp/ghc28144_0/ghc_4.c:1: /usr/local/lib/gcc5/gcc/x86_64-portbld-freebsd11.0/5.4.0/include- fixed/sys/types.h:266:9: error: error: unknown type name '__vm_ooffset_t' typedef __vm_ooffset_t vm_ooffset_t; ^ | 266 | typedef __vm_ooffset_t vm_ooffset_t; | ^ /usr/local/lib/gcc5/gcc/x86_64-portbld-freebsd11.0/5.4.0/include- fixed/sys/types.h:268:9: error: error: unknown type name '__vm_pindex_t' typedef __vm_pindex_t vm_pindex_t; ^ | 268 | typedef __vm_pindex_t vm_pindex_t; | ^ `gcc5' failed in phase `C Compiler'. (Exit code: 1) }}} On my FreeBSD 10.3 box: {{{ $ freebsd-version 10.3-STABLE $ pkg info binutils-2.28,1 GNU binary tools gcc-5.4.0_2 Meta-port for the default version of the GNU Compiler Collection gcc-ecj-4.5 Eclipse Java Compiler used to build GCC Java gcc5-5.4.0_3 GNU Compiler Collection 5 gmake-4.2.1_1 GNU version of 'make' utility gmp-6.1.2 Free library for arbitrary precision arithmetic libffi-3.2.1 Foreign Function Interface libiconv-1.14_10 Character set conversion library perl5-5.24.1_1 Practical Extraction and Report Language $ cat ./ghc-8.2.1-bin/lib/ghc-8.2.1/settings [("GCC extra via C opts", " -fwrapv -fno-builtin"), ("C compiler command", "gcc"), ("C compiler flags", " -fno-stack-protector"), ("C compiler link flags", " -fuse-ld=gold"), ("C compiler supports -no-pie", "NO"), ("Haskell CPP command","gcc"), ("Haskell CPP flags","-E -undef -traditional"), ("ld command", "ld.gold"), ("ld flags", ""), ("ld supports compact unwind", "YES"), ("ld supports build-id", "YES"), ("ld supports filelist", "NO"), ("ld is GNU ld", "YES"), ("ar command", "/usr/bin/ar"), ("ar flags", "clqs"), ("ar supports at file", "NO"), ("touch command", "touch"), ("dllwrap command", "/bin/false"), ("windres command", "/bin/false"), ("libtool command", "libtool"), ("perl command", "/usr/local/bin/perl"), ("cross compiling", "NO"), ("target os", "OSFreeBSD"), ("target arch", "ArchX86_64"), ("target word size", "8"), ("target has GNU nonexec stack", "True"), ("target has .ident directive", "True"), ("target has subsections via symbols", "False"), ("target has RTS linker", "@HaskellHaveRTSLinker@"), ("Unregisterised", "NO"), ("LLVM llc command", "llc"), ("LLVM opt command", "opt") ] $ ./ghc-8.2.1-bin/bin/ghc -O0 --make Main.hs [1 of 1] Compiling Main ( Main.hs, Main.o ) Linking Main ... $ ./Main hello, world! }}} I also noticed that using FreeBSD's strip (from elftoolchain), the {{{ Installing library in /home/ghc/lib/ghc-8.2.1/ghc-prim-0.5.1.0 "utils/ghc-cabal/dist-install/build/tmp/ghc-cabal-bindist" copy libraries /integer-gmp dist-install "strip" '' '/home/ghc' '/home/ghc/lib/ghc-8.2.1' '/home/ghc/share/doc/ghc- 8.2.1/html/libraries' 'v p dyn' }}} phase will be a bit longer than GNU's strip. (Tested by put my $LOCALBASE/bin ahead in $PATH). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14064> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14012: External interpreter fails on FreeBSD
by GHC 25 Aug '18

25 Aug '18

#14012: External interpreter fails on FreeBSD ----------------------------------------+--------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.0.1 Keywords: | Operating System: FreeBSD Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- {{{ $ inplace/bin/ghc-stage2 -fexternal-interpreter --interactive GHCi, version 8.3.20170722: http://www.haskell.org/ghc/ :? for help {handle: <file descriptor: 12>}: GHCi.Message.remoteCall: end of file }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14012> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11470: Support changing cross compiler target at runtime
by GHC 24 Aug '18

24 Aug '18

#11470: Support changing cross compiler target at runtime -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature | Status: new request | 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: -------------------------------------+------------------------------------- Relevant mailing list thread: https://mail.haskell.org/pipermail/ghc- devs/2016-January/011064.html At the moment, GHC's cross-compiling support requires you to build a cross-compiler for every target platform from scratch. (https://ghc.haskell.org/trac/ghc/wiki/CrossCompilation) There are two reasons for this: 1. GHC uses a configure script to interrogate the GCC toolchain about the vagaries of cross-compilation, some parameters of which get baked into various build system scripts and header files and such. Some of this information wends its way into the final built GHC executable. 2. GHC needs to build the boot libraries, using the stage 1 compiler, targeting the cross compiler. It would be very useful to move this configuration from configure time to run time, so that a user can use GHC as a cross-compiler without having to recompile GHC. That is, we would like to (1) ensure that any information from the configure script can alternately be supplemented at runtime, (2) that users can cross-compile the boot libraries on-demand (since GHC won't ship with the ARM versions of the boot libraries), and (3) rearchitect GHC internally so that it handles knows to keep separate the interface files/package database for various cross compilation targets. Such a change will make cross-compiling more convenient (the iOS cross- compiler currently requires GHC to be built twice, once for ARM and once for the simulator!) and will also pave the way for supporting Template Haskell and compiler plugins in the cross-compiler, since a GHC that knows how to deal with both the target and host platforms can simply ensure that it only loads code built for the host platform (a user can then, if necessary, build code twice, once for the host for Template Haskell, and once for the target). Unclear points of design: * How should GHC get the information about the GCC cross-compiler toolchain (which currently is gotten by `configure`?) Preferably, not by running a `configure` script every time you invoke it. What is this information anyway? * How should GHC rebuild the boot libraries? Maybe `cabal-install` can simply handle this for you. Note: please update the top of this ticket as the design becomes clearer. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11470> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10346: Cross-module SpecConstr
by GHC 24 Aug '18

24 Aug '18

#10346: Cross-module SpecConstr -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Type-class specialisation now happens flawlessly across modules. That is, if I define {{{ module DefineF where f :: Num a => a -> a {-# INLINEABLE f #-} f x = ...f x'.... }}} then modules that import `DefineF` and call `f` at some particular type (say `Int`) will generate a specialised copy of `f`'s code. But this does not happen for `SpecConstr`; we only specialise a function for calls made in the same module. All the infrastructure is in place to allow cross-module `SpecConstr`; it just hasn't been done yet. This ticket is to record the idea. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10346> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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