It's hard to say without reference to specifics; certainly the MD files have been around since time-immemorial, even if they've been augmented with new features over the years. And the gimple bits were primarily aimed at making the in-memory representation more efficient, a goal which they accomplished.

In any event, as you say, things have been revamped, so whatever issues there were with the old internals no longer apply, right? So there's no point in dragging out old chestnuts like "GCC can't support modern architectures or modern optimization techniques", because that's not true anymore, right?

(I apologize if this comes across as harsh; I'm just tired of seeing LLVM articles where commenters appear to be drinking the LLVM Kool-Aid without having any idea what the LLVM folks are grousing about. Sometimes the LLVM folks have a point, sometimes they're just asserting their engineering decisions are superior, which is debatable, and sometimes they're just grousing because they don't seem to like GCC. It's hard to say exactly what's in view from commenters and from the LLVM folks themselves.

GCC currently supports 8-bit microcontrollers, 32/64-bit desktop chips, a few "nonstandard" VLIW and DSP architectures, and lots of other chips in between. I, for one, am impressed with how much Clang and LLVM have done, but I'll also be more impressed if, in a decade and a half, LLVM's architecture hasn't acquired some warts and it seriously supports more than two architectures. After all, GCC was, in many ways, state-of-the-art when it first came out too...)