Isn't that one of the "slow lea" cases? https://reviews.llvm.org/D32277 (I can't quite parse whether using EBP/RBP/R13 is necessary to hit the slow case, or if it's any of those bullet points that cause slowness.)
rbp/r13 are there because the funky way x86 encodes ModR/M means that they get a "+ 0" forced onto them, i.e. [rbp + rax*8] actually must be [rbp + rax*8 + 0] and as such behaves like a 3-operand lea. (same for [rbp] → [rbp+0] but that's irrelevant here as that's still two-operand)
