Re: LW compiler optimizations

Thanks, Martin,

your response was quite enlightening and explains why we see the difference in performance well. It confirms the suspicion that we collectively came to that displaced arrays are a less preferred option when it comes to numerically intensive code.


> On 20 Jan 2025, at 20:07, Martin Simmons <[email protected]> wrote:
> 
> In LispWorks at least, a simple 1d array is a single object, where the data
> follows the type information in memory.  Displaced arrays are two objects,
> because you have the displaced array and the array that it references.  That
> make aref more complicated.
> 
> There are two additional complications:
> 
> - You can have a chain of multiple displaced arrays, so aref has to loop in
>  the general case until it reaches the simple array at the end of the chain.
> 
> - In the case of adjustable displaced arrays, the displaced array can be
>  changed on-the-fly to an array with a different size.  We ensure that this
>  on-the-fly change by adjust-array is thread-safe w.r.t. aref, which makes
>  aref to more work.
> 
> There is no type declaration to specify either of these complications, so aref
> has to assume that any non simple array might be a chain of adjustable
> displaced arrays.


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