[mono][jit] Codegen emits unnecessary stores and loads with FP function args

[jandupej]

When JITting the following function

[MethodImpl(MethodImplOptions.NoInlining)]
static float Add(float x, float y)
{
    return x + y;
}

this code is generated on arm64 Mac:

loWorld_Program_Add__single_single_:
0000000000000000        stp     x29, x30, [sp, #-0x20]! ; backing up x29,x30 which we should not need
0000000000000004        mov     x29, sp                 ; backing up sp only for the redundant stores
0000000000000008        str     s0, [x29, #0x10]        ; redundant store 1
000000000000000c        str     s1, [x29, #0x18]        ; redundant store 2
0000000000000010        ldr     s0, [x29, #0x10]        ; redundant load 1
0000000000000014        ldr     s1, [x29, #0x18]        ; redundant load 2
0000000000000018        fadd    s0, s0, s1
000000000000001c        mov     sp, x29
0000000000000020        ldp     x29, x30, [sp], #0x20
0000000000000024        ret

The function arguments are passed in regs s0 and s1. They are stored to memory and then loaded again, degrading performance. The expected codegen would look more like this:

loWorld_Program_Add__single_single_:
0000000000000000        fadd    s0, s0, s1
0000000000000004        ret

[SamMonoRT]

Assigning to @jandupej for tracking