[GHC] #12506: Compile time regression in GHC 8.
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: -------------------------------------+------------------------------------- This bug is entirely reproducible but unfortunately takes some setup. I don't have a minimal example. The regression is happening in FLTKHS (https://github.com/deech/fltkhs), the Haskell bindings to the FLTK(http://fltk.org) toolkit, and in particular to this GUI (https://github.com/deech/fltkhs/blob/master/images /tree-complex-windows.png). In GHC 7.8, it taks 5-9 seconds to compile and link in 7.10.3, that goes up to 12-15 seconds and finally in GHC 8 it shoots up to 45 seconds. While these numbers come from my i7, 16GB RAM Linux laptop, the compile time regression is proportionally reproducible across machines and operating systems. Here are the steps to reproduce it * Install FLTK Please follow the instructions here (https://github.com/deech/fltkhs #linux-and-bsd) but only the first set which about for installing FLTK 1.3. * Clone the repo with the offending application: `git clone https://github.com/deech/fltkhs-fluid-demos` * Build the application and reproduce the problem: - `cabal install fltkhs` - At the root of the repo do `cabal build fltkhs-fluid-tree` -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by deech: @@ -16,2 +16,1 @@ - #linux-and-bsd) but only the first set which about for installing FLTK - 1.3. + #linux-and-bsd) but only the first set which is about installing FLTK 1.3. New description: This bug is entirely reproducible but unfortunately takes some setup. I don't have a minimal example. The regression is happening in FLTKHS (https://github.com/deech/fltkhs), the Haskell bindings to the FLTK(http://fltk.org) toolkit, and in particular to this GUI (https://github.com/deech/fltkhs/blob/master/images /tree-complex-windows.png). In GHC 7.8, it taks 5-9 seconds to compile and link in 7.10.3, that goes up to 12-15 seconds and finally in GHC 8 it shoots up to 45 seconds. While these numbers come from my i7, 16GB RAM Linux laptop, the compile time regression is proportionally reproducible across machines and operating systems. Here are the steps to reproduce it * Install FLTK Please follow the instructions here (https://github.com/deech/fltkhs #linux-and-bsd) but only the first set which is about installing FLTK 1.3. * Clone the repo with the offending application: `git clone https://github.com/deech/fltkhs-fluid-demos` * Build the application and reproduce the problem: - `cabal install fltkhs` - At the root of the repo do `cabal build fltkhs-fluid-tree` -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * failure: None/Unknown => Compile-time performance bug -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * owner: => bgamari * priority: normal => high Comment: I'll be adding this one to my queue. Thanks deech. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by deech: @@ -21,0 +21,1 @@ + - `cabal install c2hs New description: This bug is entirely reproducible but unfortunately takes some setup. I don't have a minimal example. The regression is happening in FLTKHS (https://github.com/deech/fltkhs), the Haskell bindings to the FLTK(http://fltk.org) toolkit, and in particular to this GUI (https://github.com/deech/fltkhs/blob/master/images /tree-complex-windows.png). In GHC 7.8, it taks 5-9 seconds to compile and link in 7.10.3, that goes up to 12-15 seconds and finally in GHC 8 it shoots up to 45 seconds. While these numbers come from my i7, 16GB RAM Linux laptop, the compile time regression is proportionally reproducible across machines and operating systems. Here are the steps to reproduce it * Install FLTK Please follow the instructions here (https://github.com/deech/fltkhs #linux-and-bsd) but only the first set which is about installing FLTK 1.3. * Clone the repo with the offending application: `git clone https://github.com/deech/fltkhs-fluid-demos` * Build the application and reproduce the problem: - `cabal install fltkhs` - `cabal install c2hs - At the root of the repo do `cabal build fltkhs-fluid-tree` -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by deech: @@ -21,1 +21,1 @@ - - `cabal install c2hs + - `cabal install c2hs` New description: This bug is entirely reproducible but unfortunately takes some setup. I don't have a minimal example. The regression is happening in FLTKHS (https://github.com/deech/fltkhs), the Haskell bindings to the FLTK(http://fltk.org) toolkit, and in particular to this GUI (https://github.com/deech/fltkhs/blob/master/images /tree-complex-windows.png). In GHC 7.8, it taks 5-9 seconds to compile and link in 7.10.3, that goes up to 12-15 seconds and finally in GHC 8 it shoots up to 45 seconds. While these numbers come from my i7, 16GB RAM Linux laptop, the compile time regression is proportionally reproducible across machines and operating systems. Here are the steps to reproduce it * Install FLTK Please follow the instructions here (https://github.com/deech/fltkhs #linux-and-bsd) but only the first set which is about installing FLTK 1.3. * Clone the repo with the offending application: `git clone https://github.com/deech/fltkhs-fluid-demos` * Build the application and reproduce the problem: - `cabal install fltkhs` - `cabal install c2hs` - At the root of the repo do `cabal build fltkhs-fluid-tree` -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by deech): Replying to [comment:3 bgamari]:
I'll be adding this one to my queue. Thanks deech. Great. Let me know if I can help.
-- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by deech: @@ -20,0 +20,1 @@ + - `cabal install c2hs` @@ -21,1 +22,0 @@ - - `cabal install c2hs` New description: This bug is entirely reproducible but unfortunately takes some setup. I don't have a minimal example. The regression is happening in FLTKHS (https://github.com/deech/fltkhs), the Haskell bindings to the FLTK(http://fltk.org) toolkit, and in particular to this GUI (https://github.com/deech/fltkhs/blob/master/images /tree-complex-windows.png). In GHC 7.8, it taks 5-9 seconds to compile and link in 7.10.3, that goes up to 12-15 seconds and finally in GHC 8 it shoots up to 45 seconds. While these numbers come from my i7, 16GB RAM Linux laptop, the compile time regression is proportionally reproducible across machines and operating systems. Here are the steps to reproduce it * Install FLTK Please follow the instructions here (https://github.com/deech/fltkhs #linux-and-bsd) but only the first set which is about installing FLTK 1.3. * Clone the repo with the offending application: `git clone https://github.com/deech/fltkhs-fluid-demos` * Build the application and reproduce the problem: - `cabal install c2hs` - `cabal install fltkhs` - At the root of the repo do `cabal build fltkhs-fluid-tree` -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): The issue here seems to be the `Tree` module. With `-O1` compilation takes four minutes with much of the time being spent in the simplifier. However, deech said that his real concern was the compilation time with `-O0`. The culprit here appears to be desugaring, which takes over 10 seconds of the 30 second total compilation time (with a profiled compiler). Looking into the profile, it seems that the culprit is `simpleOptPgm`. In particular, it appears that the majority of desugaring time is spent in `optCoercion` called from the `Cast` branch of `simple_opt_expr.go`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Looking at the desugared Core of `Tree` (which is 2.4 gigabytes!) it seems we end up with lots of equivalent yet repeated equality coercions at the top level. For instance, there are 64 coercions of the form, {{{#!hs -- RHS size: {terms: 2, types: 22, coercions: 691} $d~_aDMR :: (Match (Graphics.UI.FLTK.LowLevel.Hierarchy.CMenuItem Base) :: *) ~ (FindOp MenuItem MenuItem (SetLabelsize ()) :: *) }}} However, it turns out that this is a drop in the bucket compared to, {{{ -- RHS size: {terms: 8,634, types: 10,620, coercions: 1,621,550} make_window :: IO (Ref Window) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): I clarify that I suspect the large term counts here are really the result of the library itself making heavy use of type classes, essentially making this yet another manfestation of #8095. The high desugaring times observed in compiling tree are due to the fact that we run `simpleOptPgm` during desugaring. I didn't have a chance to look at compilation time regressed from 7.8 to 7.10 to 8.0. When I get a chance the best next step will likely to focus on the 7.10 to 8.0 regression (since it is both newer (and therefore easier to debug) as well as larger). First verify that the desugared Core is equivalent, then look at compiler profiles to see if the compiler implementation has regressed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Based on the date, it appears this ticket likely refers to `fltkhs-0.4.0.9` (commit 60ace4c5e7743f5a24ac959fba877aeb27d80618) from June 25, 2016. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by deech): This is still reproducible from the latest [https://hackage.haskell.org/package/fltkhs-0.5.3.4 FLTKHS] with GHC 8.0.2. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): It appears that the absurd number of coercions is present in 7.10 as well as 8.0. So we'll need to look at something else to find the perf difference between those versions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): I tried reproducing the problem with GHC 8.2.1, but unfortunately the build instructions no longer work with Cabal 2.0.x. It seems that `fltkhs` doesn't support Cabal 2.0, and [this github issue](https://github.com/deech/fltkhs/issues/38) tells me this might not get fixed anytime soon. Is there an up-to-date way of reproducing the issue that I could use? Preferably one that doesn't involve `stack`, simply because I want to hook a custom-built GHC directly from git into the build so I can play with some things and cherry-pick selected changes, and this isn't trivial with stack. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by deech): Replying to [comment:14 tdammers]:
I tried reproducing the problem with GHC 8.2.1, but unfortunately the build instructions no longer work with Cabal 2.0.x. It seems that `fltkhs` doesn't support Cabal 2.0, and [this github issue](https://github.com/deech/fltkhs/issues/38) tells me this might not get fixed anytime soon.
Is there an up-to-date way of reproducing the issue that I could use? Preferably one that doesn't involve `stack`, simply because I want to hook a custom-built GHC directly from git into the build so I can play with some things and cherry-pick selected changes, and this isn't trivial with stack.
I should have closed that issue, the [master branch](https://github.com/deech/fltkhs) and the latest [stable release](https://hackage.haskell.org/package/fltkhs) [should](https://github.com/deech/fltkhs/blob/master/Setup.hs#L47) work with Cabal 2.0.0.2 and GHC 8.2.1. I'm happy to help you through it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by deech): I've put together a [https://github.com/deech/Trac12506 reduced example] that has the same issues. It's much easier to work with. In putting this together I noticed there is a vast difference in compilation time and memory between GHC 8.02 and GHC 8.22; the former takes 45 seconds and uses 1.4GB RAM to compile, the latter, 10 seconds and 200 MB so that is a great improvement. However while compilation speed is much improved between 8.0.2 and 8.2.2 that still only brings it up to par with GHC 7.10 which is GHC version against which I reported the issue in the first place so the problem still exists. Hopefully this reduced example helps clarify the underlying issue. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by deech): I've added a rough [https://github.com/deech/Trac12506#compile-timememory- usage-comparisons comparison table] showing compile times and memory usage going back to 7.8.4. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Thanks deech! We can try to have someone look at this soon. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
I've put together a [https://github.com/deech/Trac12506 reduced example]
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): Replying to [comment:16 deech]: that has the same issues. It's much easier to work with. In putting this together I noticed there is a vast difference in compilation time and memory between GHC 8.02 and GHC 8.22; the former takes 45 seconds and uses 1.4GB RAM to compile, the latter, 10 seconds and 200 MB so that is a great improvement.
However while compilation speed is much improved between 8.0.2 and 8.2.2
that still only brings it up to par with GHC 7.10 which is GHC version against which I reported the issue in the first place so the problem still exists.
Hopefully this reduced example helps clarify the underlying issue.
Great, that makes things so much easier! Thanks a lot, I'll look into it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): OK, got it compiled against GHC head. The output of `-ddump-timings` shows two obvious suspects: {{{ [5 of 5] Compiling Main ( app/Main.hs, app/Main.o ) *** Parser [Main]: Parser [Main]: alloc=14721280 time=9.927 *** Renamer/typechecker [Main]: Renamer/typechecker [Main]: alloc=585898184 time=956.617 *** Desugar [Main]: Desugar [Main]: alloc=76966472 time=214.242 *** Simplifier [Main]: Simplifier [Main]: alloc=3469053424 time=2430.489 *** CoreTidy [Main]: CoreTidy [Main]: alloc=220130032 time=371.644 *** CorePrep [Main]: CorePrep [Main]: alloc=7744 time=0.030 *** CodeGen [Main]: CodeGen [Main]: alloc=3436008728 time=4730.477 Linking app/Main ... }}} In other words, while compiling `Main`, we get very long timings on the Simplifier and CodeGen steps. I suspect that the latter is caused by the former. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:20 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): It turns out that `Main.hs` produces about 2.8G of Core. This part seems to be the culprit: {{{ -- RHS size: {terms: 6,002, types: 8,003, coercions: 1,415,000, joins: 0/0} main :: IO () }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): That's one big coercion! Can you distil a standalone test case? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): I tried, however concatenating the relevant modules into one reduces the impact a bit. I'll attach a reduced version anyway, where we still get this: {{{ -- RHS size: {terms: 8, types: 11, coercions: 1,424, joins: 0/0} main :: IO () }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by tdammers): * Attachment "test.hs" added. Test case to reproduce -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): Copying the last line a thousand times or so over increases the number of coercions to similar levels as the original one, but this simpler cases makes the dumped Core easier to handle. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:24 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): - Make sure this is truly a regression - Figure out whether the huge coercion is actually the cause - Bisect? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * milestone: => 8.4.1 Comment: For the record, this is another case which would stand to be improved by the coercion dropping proposed in #8095. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:26 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): I can confirm that this *is* a regression; I'm seeing ~34 seconds overall compilation time on 7.10.3, vs. ~341 seconds on GHC HEAD. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:27 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by tdammers): * Attachment "test1000.hs" added. The actual test input used when comparing 7.10.3 against HEAD (8.4.x) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
I can confirm that this *is* a regression; I'm seeing ~34 seconds overall compilation time on 7.10.3, vs. ~341 seconds on GHC HEAD.
Aha! Excellent. Does that show on (some version of) the repro case test.hs? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:28 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): Replying to [comment:28 simonpj]:
I can confirm that this *is* a regression; I'm seeing ~34 seconds overall compilation time on 7.10.3, vs. ~341 seconds on GHC HEAD.
Aha! Excellent. Does that show on (some version of) the repro case test.hs?
PS: maybe comment:27 answers that affirmatively; I missed that.
Yes on both; `test1000.hs` is pretty much an exact replica of the code in the original test case, I really just unrolled the imports to get it into one file, and played with the number of repetitions in `main`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:29 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): The problem persists with D4394 applied, so the idea that that particular nonlinearity in the coercion handling has anything to do with it doesn't hold. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:30 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
The problem persists with D4394 applied
I was not expecting that D4394 would help. The problem here is that the coercions are too big. The encouraging news is that 7.10.3 didn't have that problem, so it's an existence proof that we don't ''need'' big coercions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:31 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12506: Compile time regression in GHC 8. -------------------------------------+------------------------------------- Reporter: deech | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I've had a look. I don't think it's fruitful for you to investigate further, Tobias, until I or Richard have had a look at the constraints generated etc. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12506#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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