Function powi_intrinsic 

fn powi_intrinsic<'tcx, S: Semantics>(
    this: &mut MiriInterpCx<'tcx>,
    args: &[OpTy<'tcx>],
    dest: &MPlaceTy<'tcx>,
) -> InterpResult<'tcx, ()>
where
    IeeeFloat<S>: HostFloatOperation + IeeeExt + Float + Into<Scalar>,