Regression in recompilation

[lxvm]

Hi,

I was benchmarking some functions and noticed that loading Revise is leading to unnecessary recompilation of functions on v3.13.1 and Julia v1.12.4 using the following benchmark:

using Revise
function bcastbench!(a, b, c)
    broadcast!(*, a, b, c)
    return a
end
nbase = 2^24
nbatch = 12
a1 = Array{ComplexF64}(undef, nbase, nbatch)
b1 = rand(ComplexF64, nbase, nbatch)
c1 = rand(ComplexF64, nbase, nbatch)

bcastbench!(a1, b1, c1); # first run for compilation
@time bcastbench!(a1, b1, c1);
@time bcastbench!(a1, b1, c1);
@time bcastbench!(a1, b1, c1);

The timed runs shouldn't have to compile bcastbench!, however they do in Julia v1.12.4 with Revise loaded as shown in the results here:

$ julia +lts --startup-file=no bcastbench.jl # v1.10.10 with Revise v3.13.1 unaffected
  0.479097 seconds
  0.482854 seconds
  0.482950 seconds
$ julia +release --startup-file=no bcastbench.jl # v1.12.4 with Revise v3.13.1 regression
  0.740573 seconds (1.08 M allocations: 58.439 MiB, 91.25% compilation time)
  0.785327 seconds (1.19 M allocations: 58.842 MiB, 96.01% compilation time)
  0.839740 seconds (1.27 M allocations: 62.654 MiB, 102.61% compilation time)

The slowdown is confusing for benchmarks, but only a minor inconvenience on my Debian machine. However, on my M3 Macbook, the recompilation takes longer and longer on each trial and takes an increasing amount of memory and time (several Gigabytes and a minute to run by the third trial) to the point it necessitates a change in workflow.

Why would Revise be recompiling unnecessarily? This appears to be a regression.

[lassepe]

While I do not see a noticable latency regression on Ubuntu 22.04, at least I can reproduce that there is re-compilation. Interestingly, depends on whether there is more than one thread (interactive or not):

/tmp via ஃ v1.12.4
❯ ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/bin/julia --threads=1,0 --startup-file=no bcastbench.jl
  0.464103 seconds
  0.466438 seconds
  0.464092 seconds

/tmp via ஃ v1.12.4
❯ ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/bin/julia --threads=1,1 --startup-file=no bcastbench.jl
  0.455911 seconds (574.62 k allocations: 27.681 MiB, 101.76% compilation time)
  0.463287 seconds (479.93 k allocations: 26.355 MiB, 99.34% compilation time)
  0.455429 seconds (450.06 k allocations: 24.866 MiB, 97.29% compilation time)

/tmp via ஃ v1.12.4
❯ ~/.julia/juliaup/julia-1.12.4+0.x64.linux.gnu/bin/julia --threads=2,0 --startup-file=no bcastbench.jl
  0.464407 seconds (643.37 k allocations: 30.838 MiB, 100.01% compilation time)
  0.467069 seconds (594.95 k allocations: 28.973 MiB, 102.90% compilation time)
  0.466339 seconds (508.55 k allocations: 29.372 MiB, 97.30% compilation time)