Clash slow on Windows using GHC 9.8

[christiaanb]

Observed on the CI runs of #2768, I see that running the vector testsuite takes:

• On GHC 9.4: 7m19s https://github.com/clash-lang/clash-compiler/actions/runs/10091542369/job/27903324484
• On GHC 9.8: 1h32m57s https://github.com/clash-lang/clash-compiler/actions/runs/10091542369/job/27903324825

[martijnbastiaan]

9.6 too: https://github.com/clash-lang/clash-compiler/actions/runs/10124978202/job/27999943983?pr=2777

[martijnbastiaan]

This could be the same as what doctest-parallel is experiencing. I've collected some results.

A few observations observations:

• Performance has gradually been declining on Windows
• It got very bad with 9.6

I don't think there is a point in comparing the timings between OSes directly. I don't know what hardware is picked for each OS.

Windows

GHC	doctests	spectests	example project
8.4.4	4	65	30
8.6.5	3	66	29
8.8.4
8.10.7	3	83	40
9.0.2	4	78	30
9.2.8	4	85	30
9.4.7	4	101	26
9.6.3	14	351	30
9.8.1	14	338	31

doctest-parallel is broken on 8.8.4 on Windows.

Linux

GHC	doctests	spectests	example project
8.4.4	0	20	19
8.6.5	0	26	19
8.8.4	1	27	20
8.10.7	1	27	20
9.0.2	1	29	19
9.2.8	0	27	18
9.4.7	0	27	19
9.6.3	1	27	14
9.8.1	1	24	21

macOS

GHC	doctests	spectests	example project
8.4.4
8.6.5
8.8.4
8.10.7
9.0.2
9.2.8	2	44	19
9.4.7	1	41	20
9.6.3	1	31	19
9.8.1	2	30	21

doctest-parallel's CI is broken on 8.4.4-9.0.2 on macOS.

[martijnbastiaan]

I've spun up a bunch of CI jobs to test cabal run doctest on doctest-parallel. It seems that a patch introduced in 9.8 but backported to 9.6.3 and 9.4.8 causes issues. Note that the 9.4 job you linked runs on 9.4.7, which doesn't have that patch yet.

Results

os	ghc	mean
windows-latest	9.10.1	14.37
windows-latest	9.8.2	15.82
windows-latest	9.8.1	13.63
windows-latest	9.6.6	14.80
windows-latest	9.6.5	14.18
windows-latest	9.6.4	13.75
windows-latest	9.6.3	13.61
windows-latest	9.6.2	4.48
windows-latest	9.6.1	4.88
windows-latest	9.4.8	14.08
windows-latest	9.4.7	4.79
windows-latest	9.4.6	4.39
windows-latest	9.4.5	4.25
windows-latest	9.4.4	4.50
windows-latest	9.4.3	4.53
windows-latest	9.4.2	4.53
windows-latest	9.4.1	4.89
windows-latest	9.2.8	4.16
windows-latest	9.2.7	3.82
windows-latest	9.2.6	3.62
windows-latest	9.2.5	3.42
windows-latest	9.2.4	3.60
windows-latest	9.2.3	3.66
windows-latest	9.2.2	3.58
windows-latest	9.2.1	3.65
windows-latest	8.10.7	3.58
windows-latest	8.10.6	3.63
windows-latest	8.10.5	3.53
windows-latest	8.10.4	3.88
windows-latest	8.10.3	3.75
ubuntu-24.04	9.10.1	0.89
ubuntu-24.04	9.8.2	0.85
ubuntu-24.04	9.8.1	0.90
ubuntu-24.04	9.6.6	0.89
ubuntu-24.04	9.6.5	0.86
ubuntu-24.04	9.6.4	0.90
ubuntu-24.04	9.6.3	0.91
ubuntu-24.04	9.6.2	0.92
ubuntu-24.04	9.6.1	0.90
ubuntu-24.04	9.4.8	0.88
ubuntu-24.04	9.4.7	0.92
ubuntu-24.04	9.4.6	0.92
ubuntu-24.04	9.4.5	0.88
ubuntu-24.04	9.4.4	0.87
ubuntu-24.04	9.4.3	0.87
ubuntu-24.04	9.4.2	0.86
ubuntu-24.04	9.4.1	0.86
ubuntu-24.04	9.2.8	0.99
ubuntu-24.04	9.2.7	0.89
ubuntu-24.04	9.2.6	0.94
ubuntu-24.04	9.2.5	0.89
ubuntu-24.04	9.2.4	0.90
ubuntu-24.04	9.2.3	0.89
ubuntu-24.04	9.2.2	0.90
ubuntu-24.04	9.2.1	0.88
ubuntu-24.04	8.10.7	0.95
ubuntu-24.04	8.10.6	0.93
ubuntu-24.04	8.10.5	0.94
ubuntu-24.04	8.10.4	0.94
ubuntu-24.04	8.10.3	0.95
ubuntu-24.04	8.10.2	0.94
ubuntu-24.04	8.10.1	1.06