To a large degree, constant-time programming is hampered by the fact that even hardware is often unwilling to provide constant-time guarantees, let alone any guarantees that the compiler would care to preserve. (Although, to be honest, constant-time guarantees are the sort of things that most compiler writers prefer to explicitly not guarantee in any circumstances whatsoever).
Your comment makes me wonder about the idea of building a superscalar, out of order, speculative implementation of the 6502 or 8080 instruction sets. Might make a good educational project.
