struct s {
  int a[256];
  int b;
};

void f0(struct s s)
{
}

void f1(struct s s)
{
  f0(s);
}

---

stefan@wonka:~$ ~/milkymist/llvm/bin/clang -ccc-host-triple lm32 -c -S struct_byval.c -o -
        .file   "struct_byval.c"
        .text
        .globl  f0
        .type   f0,@function
f0:
        ret
.Ltmp0:
        .size   f0, .Ltmp0-f0

        .globl  f1
        .type   f1,@function
f1:
        addi     sp, sp, -16
        sw       (sp+16), ra
        sw       (sp+12), fp
        addi     fp, sp, 20
        sw       (fp+-12), r1
        calli    f0
        lw       r1, (fp+-12)
        sw       (fp+-16), r1
        lw       fp, (sp+12)
        lw       ra, (sp+16)
        addi     sp, sp, 16
        ret
.Ltmp1:
        .size   f1, .Ltmp1-f1