The short answer is none of them are guaranteed to live on the stack (or actually to even live anywhere). One major advantage julia’s compiler has over c/c++ is that it makes far fewer guarantees about how it will implement your code. C and c++ compilers are forced to compile the actual code you wrote more often, even when there was a different way that would have gotten the same algorithm faster. Julia, on the other hand gives itself more room to change the details as long as it can prove you won’t notice the difference. One example of this is that it will often not store StaticArrays anywhere in memory, and just use a few registers instead. This is an optimization c won’t often do because for it to be valid, the compiler has to prove that you haven’t done something ugly like take the address of an integer that happens to refer to the memory location of the array.
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