At the time I worked for a small compiler company (primarily C and secondarily Fortran) that did a port for the i860, but decided not to polish and market it. I

At the time I worked for a small compiler company (primarily C and secondarily Fortran) that did a port for the i860, but decided not to polish and market it. It was a while ago, but my memory matches what jandrese (parent comment) says. It's not that it was particularly hard to compile for — it did have specific multiple-issue rules, but we were used to worse from microcode and VLIW targets — but that, outside of a very few arithmetic kernels, real-world code simply did not have enough parallelism for the chip to get anywhere near its paper performance claims. Entering and leaving the multi-flop mode had high latency, and there was so much internal state that interrupts/task-switching were ridiculously expensive. It was predictable that it was not going to be succeed as a general-purpose processor.