# What LLVM version to use, 10, 11 possible? And how to reduce startup time (for the Benchmark Game)?

**URL:** <https://discourse.julialang.org/t/what-llvm-version-to-use-10-11-possible-and-how-to-reduce-startup-time-for-the-benchmark-game/36743>\
**Category:** Performance\
**Created:** [March 30, 2020, 2:48pm UTC](https://discourse.julialang.org/t/what-llvm-version-to-use-10-11-possible-and-how-to-reduce-startup-time-for-the-benchmark-game/36743 "2020-03-30T14:48:17Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Palli](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/palli/32/3380_2.png) [@Palli](https://discourse.julialang.org/u/Palli)\
**Post date:** [March 30, 2020, 2:48pm UTC](https://discourse.julialang.org/t/what-llvm-version-to-use-10-11-possible-and-how-to-reduce-startup-time-for-the-benchmark-game/36743/1 "2020-03-30T14:48:17Z")

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A.  
I know I’m using LLVM 9.0.1, but is latest 10 (or 11) coming to master?

I’m just curious if Julia will optimize better (it’s already good, better than C), no rush.

It seems JuliaLang/julia uses LLVM, not LLVM from Yggrasil (where there is version 10).

I’m a bit confused seeing 8 here, and 9 before, what’s he meaning of that:

> <https://github.com/JuliaBinaryWrappers/LLVM_full_jll.jl/commit/a8db8446c8bbb765249ea65f0e1388c8cfdc245b>

and what is:

> **[GitHub - JuliaBinaryWrappers/LLVM\_full\_assert\_jll.jl](https://github.com/JuliaBinaryWrappers/LLVM_full_assert_jll.jl)**
>
> Contribute to JuliaBinaryWrappers/LLVM\_full\_assert\_jll.jl development by creating an account on GitHub.

Can you switch LLVM at runtime?

B.  
I was looking into Fasta at the Benchmark Game, and despite i looking to be 2.3x slower than Haskell (fastest) and C, it’s actually faster than the C code on my machine, when excluding the startup cost:

> **[fasta - Which programs are fastest? (Benchmarks Game)](https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/fasta.html)**
>
> fasta - Which programs are fastest? — How fast programs generate and write random DNA sequences.

With PackageCompiler.jl I can reduce the startup cost, but not to zero as in the REPL. I know about the filtered option, how much is possible to filter out in theory? All but the GC? E.g. LLVM (for that program, I know, in general you might need it it). That program (and most) reles in the GC (and Base.Threads and IO), but let’s say it wouldn’t, could you also strip out the GC?

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**Author:** ![non-Jedi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/non-jedi/32/3645_2.png) [@non-Jedi](https://discourse.julialang.org/u/non-Jedi)\
**Post date:** [March 30, 2020, 3:02pm UTC](https://discourse.julialang.org/t/what-llvm-version-to-use-10-11-possible-and-how-to-reduce-startup-time-for-the-benchmark-game/36743/2 "2020-03-30T15:02:43Z")

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A. LLVM 8 is used for julia 1.4. In general, you shouldn’t expect newer versions of LLVM to magically speed up code (sometimes it does, and that’s a nice surprise). Looks like LLVM 10 support is at least in-progress on master. Switching llvm used for codegen at runtime probably isn’t possible (but someone may contradict me on this).

B. Hi. I wrote that Fasta benchmark. There’s definitely room for improvement there. In general, I’ve found that using Channels has a large negative effect on compile-time. If you want to speed it up, the best way would be to rewrite it in a way that doesn’t rely on Channels. 🙂 You’ll get a lot more mileage out of that than the more exotic changes you’re suggesting.

The maintainer of the benchmarksgame isn’t likely to alter the Julia benchmarks to use a compile step like PackageCompiler (from previous conversations I’ve had with him).

Also, GC isn’t a standard library, so the standard library filtering option in PackageCompiler doesn’t apply. In general, filtering standard libraries shouldn’t affect performance; only the size of binary generated.

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**Author:** ![Palli](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/palli/32/3380_2.png) [@Palli](https://discourse.julialang.org/u/Palli)\
**Post date:** [March 30, 2020, 4:01pm UTC](https://discourse.julialang.org/t/what-llvm-version-to-use-10-11-possible-and-how-to-reduce-startup-time-for-the-benchmark-game/36743/3 "2020-03-30T16:01:21Z")

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Yes, I know filtering will not affect the generated assembly.

Your program seems fastest as is, not sure about any definite improvement at runtime (only at compile time? and yes I want it excluded from the “runtime”…):

```julia
julia> include("Fasta/src/Fasta.jl")

julia> @btime Fasta.fasta(25000000, devnull)
  985.302 ms (41595 allocations: 956.91 MiB)

[The C program (and I guess the Haskell program, claimed fastest) is over 1 sec on my machine.]

However (next line applies to above and below):
$ export JULIA_NUM_THREADS=4

$ time julia-1.5-012b270df6/bin/julia -O3 -- fasta.jl 25000000 >/dev/null

real	0m2.019s
user	0m5.920s
sys	0m0.559s

$ time FastaAppCompiled/bin/Fasta 25000000 >/dev/null

real	0m1.786s
user	0m5.759s
sys	0m0.598s

```

I do not recall if I used this to compile your program:

export JULIA\_LLVM\_ARGS=-unroll-threshold=500

but it didn’t seem to matter, maybe with other value?

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**Author:** ![Palli](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/palli/32/3380_2.png) [@Palli](https://discourse.julialang.org/u/Palli)\
**Post date:** [March 30, 2020, 4:03pm UTC](https://discourse.julialang.org/t/what-llvm-version-to-use-10-11-possible-and-how-to-reduce-startup-time-for-the-benchmark-game/36743/4 "2020-03-30T16:03:32Z")

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> [@non-Jedi](#):
>
> I’ve found that using Channels has a large negative effect on compile-time

Interesting, but wouldn’t apply to PackageCompiler at runtime?