AVX help: matrix multiplication

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C++

AVX

I am trying to multiply scalars then vectors later on using Microsoft visual studio and in C++.

Essentially I copied a programme from here Using AVX instructions in matrix multiplication | Thinking and Computing[^]

I wanted to have a working model to base everything off and understand AVX better, but i come across errors reading like this:
identifier " __builtin_ia32_loadups256" is undefined.

Also on that website it have a compile with:
g++ -O3 -mavx main.cpp -o avxtest

what is this and can I do it on MVS

Thanks Matt

What I have tried:

General bits of faultfinding as i'm sure you can tell i'm still a novice when it comes to programming.