Sub-optimal code generated for certain calls to functions with auto ref qualified parameters

[Per Nordlöw]

As a follow-up to recent discussions at

https://github.com/dlang/dmd/pull/11000

I wonder if the compiler generates sub-optimal code for functions 
with `auto ref` parameters when passed l-values to parameters 
whose type fit in registers.

For instance,

T square_nt(T)(immutable scope T x)
{
     return x*x;
}

T square_t(T)(const auto ref scope T x)
{
     return x*x;
}

@safe pure nothrow @nogc unittest
{
     long x;
     auto y = square_nt(x); // passed via register
     auto z = square_t(x); // passed via indirection
}

According to my interpretation of

https://d.godbolt.org/z/5G4Eqn

it does.