// ASM stream — read-write (`+`) place output on x86_64 (cross-arch sibling of
// the aarch64 1650). `incq %[v]` reads the operand register, increments it, and
// the result is stored back through the place. Locks the x86 lowering of `+`:
// an output `=r` plus a tied input (`=r,0`) seeded with the place's value.
// x86-pinned via `.build`: ir-only here (the `.ir` is the assertion), runs
// natively on x86_64-linux (main returns 0 on success, 1 if the asm misbehaved).
bump :: () -> i64 {
    x : i64 = 41;
    asm volatile { "incq %[v]", [v] "+r" -> @x };
    return x;   // 42
}
main :: () -> i64 { if bump() != 42 { return 1; } return 0; }