[rep_lodsb]

I know Turbo Pascal produces really bad code (even in later versions), but it's not on the same level as a non-optimized Forth. Function prologue on x86 doesn't have much overhead either.

It's somewhat closer for 8-bit processors, the most popular ones had either no convenient addressing mode for stack frames at all, or an extremely slow one, like IX/IY on the Z80. For even more primitive CPUs, you might already need a virtual machine to make it "general-purpose programmable" at all -- for example if there is only one memory address register, and no way to save its contents without clobbering another one. I think that some of Chuck Moore's earliest Forth implementations were for architectures like that.

Also memory constraints could have been more important than efficiency of course. I'm not saying Forth is worthless, but it's not competing with any compiled language in terms of speed, and IMHO it also does away with too many "niceties" like local variables or actually readable syntax. Your mileage may vary :)