I have been reading about SIMD for some time and I am going through the slides over at Insomniac Games.
I like the idea and I am certainly open to making my code run more efficiently but I am just not clear how to get started with SIMD in terms of higher level code design.
For instance, let's assume that I am using a language low-level enough to let me know what the memory layout of arrays or classes is, e.g. C++.
If I now have a class such as User with attributes user_id or user_name, as a person modelling the domain that I am in, I know that I will be able to put users into hashmaps, or perhaps into arrays, vectors, or maybe sets, all depending on a particular use-case that a given User is needed in.
That is, I have a reusable User object and what data structure these objects are in is something independent of the User class's own internal structure.
Now, all the SIMD guides say, and I understand why, that instead of arrays-of-structures I should be using structures-of-arrays.
This makes sense as far SIMD instructions go but I cannot find a way to reconcile it with the fact that I am not starting with an array-of-structures that I can easily turn into a structure-of-arrays. Instead, I am starting with User. Sometimes users - in the sense of references to User objects - will be in arrays, sometimes in hashmaps, sometimes in other containers.
But this is not a scenario that online guides mention - all of them just say to turn AOS into SOA and again, I understand why, it is just that it is not a starting position of mine.
I feel that there is a gap that I just cannot make a leap over because I cannot find more complex examples. For instance, maybe I should keep user-related data in, say, two places, one is the User object for general ad-hoc access and another in SOA for SIMD instructions?
Put more generally, how does one model more object-oriented design into SIMD?
Or do people designing entire applications with SIMD in mind do not adhere to such OO concerns at all, instead opting for more data-oriented design?
Or perhaps SIMD is limited to selected modules in one's codebase and such a translation between OOP and SIMD takes place in runtime when needed (i.e. the actual data is kept both in User objects and in SOA and there is manual code to keep them in sync).
I would appreciate it if people with SIMD experience could shed more light on it from a higher level perspective. Thank you.