I think X86 processors since the Pentium Pro (mid-late 90's) have been converting the instructions into internal micro-ops. If it was feasible/efficient then it will now be quite a small block of logic. While there will be some time used to decode there is also time saved in having denser code (more code cached, less memory bandwidth used). It is far from clear that the overall effect is slower.

I would turn it round to you and ask you to cite something showing that the translation is something that does cause significant performance loss.