// or return 0 if they cannot be combined.
func mergePPC64SldiSrw(sld, srw int64) int64 {
	if sld > srw || srw >= 32 {
		return 0
	}
	mask_r := uint32(0xFFFFFFFF) >> uint(srw)
	mask_l := uint32(0xFFFFFFFF) >> uint(sld)
	mask := (mask_r & mask_l) << uint(sld)
	return encodePPC64RotateMask((32-srw+sld)&31, int64(mask), 32)
}

// Convert a PPC64 opcode from the Op to OpCC form. This converts (op x y)