For a general reference, here [0] (PDF) is a somewhat detailed description (that is, it actually discusses how this particular implementation solves the problems that arise before it) of an out-of-order implementation for a simplistic RISC ISA. Suffice to say, it doesn't really have all that much in common with the classical 5-stage RISC pipeline.

[0] https://user.eng.umd.edu/~blj/risc/RiSC-oo.1.pdf

I'm often dismissive of RISC-V posts, but I really loved this one. It does a great job of presenting the material: good graphics, readable text and references at the bottom of the text. I've been focused on smaller CPUs on durt cheap process nodes, but this was great.

Title should be "Out of Order RISC-V core from scratch - Specula". Don't know why it was changed.

Is there an open bluespec sim?