Optimizing Common Lisp

Re:Optimizing Common Lisp by metroholografix on Wednesday May 07, 2025 @05:02PM (#43920526)

I see the following in code written by newcomers to CL frequently:

    (optimize (speed 3) (safety 0))

but it is a very bad habit to get used to, in general, and may create the impression that it's needed for optimized code. Instead, use this where needed:

    (optimize (speed 3) (safety 1))

which will result in roughly same performance for the vast majority of cases, but keep array bounds checks and (weaker) type checks.

For SBCL, there's also the excellent sb-simd [1] plus compiler macros and even hooking into some of the VM internals for custom code generation [2].

[1] https://www.sbcl.org/manual/#sb_002dsimd

[2] https://pvk.ca/Blog/2014/03/15/sbcl-the-ultimate-assembly-co...

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Re:Optimizing Common Lisp by tmtvl on Wednesday May 07, 2025 @05:19PM (#43920666)

If I remember correctly there are 5 optimization settings:

1. Speed

2. Debug

3. Safety

4. Size

5. Compilation speed.

I don't think those last two have much of an impact, but the first three are the ones you want to adjust to your use case.

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Re:Optimizing Common Lisp by colingw on Thursday May 08, 2025 @12:47AM (#43923133)

Thanks for the tip. I double-checked, and while there is no difference between 0 and 1 for SBCL and ABCL, there is a slowdown for ECL.

I've elaborated here:

https://www.fosskers.ca/en/blog/optimizing-common-lisp#orgb5...

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