You're not really "giving up" portability, only with ANSI C. For all architectures where GCC is available, its labels-as-values support will happily compile and hence give you a fully portable instruction dispatch.

Regarding the threaded code: the literature seems to be horribly inconsistent in this regard. Token threaded code might actually refer to indirect-threaded code depending on what the author has read. I was actually quite surprised to read what "indirect threaded code" originally meant when I read Debaere and van Campenhout's 1990 book "Interpretation and Instruction Path co-processing".

Regarding the effect of CSE & tail-merging: I have only seen GCC to do this once, by disabling basic block reordering (-fno-reorder-blocks, due to a so-called "software trace cache"), otherwise this has never happened to me. Since I have nothing but the highest respect for Mike Pall, I guess that he might have experienced this for Lua, which has--to the best of my knowledge--less than 40 instructions. I will try to verify this on the weekend.