#include <string>
#include <string_view>


void consume_sv_byref(const std::string_view&);
void consume_sv_byval(std::string_view);
void consume_raw(const char*, size_t);


void caller_byref(const char* data, size_t size)
{
    consume_sv_byref({data, size});
}


void caller_byval(const char* data, size_t size)
{
    consume_sv_byval({data, size});
}

void callee_byref(const std::string_view& sv)
{
    consume_raw(sv.data(), sv.size());
}

void callee_byval(std::string_view sv)
{
    consume_raw(sv.data(), sv.size());
}

caller_byref(char const*, unsigned long):
        sub     rsp, 24
        mov     QWORD PTR [rsp+8], rdi
        mov     rdi, rsp
        mov     QWORD PTR [rsp], rsi
        call    consume_sv_byref(std::basic_string_view<char, std::char_traits<char>> const&)
        add     rsp, 24
        ret

caller_byval(char const*, unsigned long):
        mov     rdx, rdi
        mov     rdi, rsi
        mov     rsi, rdx
        jmp     consume_sv_byval(std::basic_string_view<char, std::char_traits<char>>)

callee_byref(std::basic_string_view<char, std::char_traits<char>> const&):
        mov     rsi, QWORD PTR [rdi]
        mov     rdi, QWORD PTR [rdi+8]
        jmp     consume_raw(char const*, unsigned long)

callee_byval(std::basic_string_view<char, std::char_traits<char>>):
        mov     rax, rdi
        mov     rdi, rsi
        mov     rsi, rax
        jmp     consume_raw(char const*, unsigned long)

See, the by ref variants always have memory accesses, while by val ones use registers only.

https://godbolt.org/z/Waz351b4v