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Fix false llvm.assumes in wake_thread! (segfault on Julia nightly) #67

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Merged
ranocha merged 2 commits into from
Oct 14, 2026
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Fix false llvm.assumes in wake_thread! (segfault on Julia nightly) #67

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b8ae5f1
Fix false llvm.assume in wake_thread! on Julia 1.13+
vchuravy Oct 13, 2026
4f1a898
CI: run the Julia nightly tests weekly
vchuravy Oct 13, 2026
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5 changes: 5 additions & 0 deletions .github/workflows/ci-julia-nightly.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,11 @@ on:
- 'LICENSE.md'
- 'README.md'
- '.github/workflows/TagBot.yml'
# Julia nightly changes without any change here (e.g. new LLVM versions, see #66),
# so also test it regularly.
schedule:
- cron: '17 4 * * 1' # weekly, Monday 04:17 UTC
workflow_dispatch:
jobs:
test-julia-nightly:
timeout-minutes: 30
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10 changes: 8 additions & 2 deletions src/threadtasks.jl
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Expand Up @@ -61,12 +61,18 @@ end
@noinline function wake_thread!(_tid::T) where {T<:Integer}
tid = _tid % Int
tidp1 = tid + one(tid)
# `Base.Workqueues` holds one queue per thread; `tidp1` must be a valid thread id.
# On Julia 1.13+ `Base.Workqueues` is a `OncePerThread`, and `Base.Workqueues()` is
# the *current* thread's queue, so its `length` is the number of queued tasks, not
# the number of threads. Assuming that count is `> tid` is false in general and lets
# LLVM 22 (Julia 1.14) miscompile the `length` loop (segfault).
@static if VERSION >= v"1.13-"
assume(unsigned(length(Base.Workqueues())) > unsigned(tid))
assume(unsigned(Threads.maxthreadid()) > unsigned(tid))
else
assume(unsigned(length(Base.Workqueues)) > unsigned(tid))
end
assume(unsigned(length(TASKS)) > unsigned(tidp1))
# `TASKS[tid]` is accessed below; `tid` ranges over `1:length(TASKS)`.
assume(unsigned(length(TASKS)) >= unsigned(tid))
@inbounds push!(Base.Workqueues[tidp1], TASKS[tid])
ccall(:jl_wakeup_thread, Cvoid, (Int16,), tid % Int16)
end
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