There are architecture-level alternatives to Speculative execution for high-performance compute - namely VLIW and the "tweaks" on it that efforts like The Mill

There are architecture-level alternatives to Speculative execution for high-performance compute - namely VLIW and the "tweaks" on it that efforts like The Mill are working on right now. The main problem with them is that they make the processor ISA inherently dependent on the actual details of its hardware configuration (you don't have a single ISA like with RISC, which can seamlessly scale from tiny micro-controller hardware to supercomputer- or datacenter-scale). But once you're willing to bite that bullet, and perhaps the vast majority of the software you use gets distributed in either source-code or arch-independent "VM" format, it can become a very attractive choice. Yes we used to think that compilers would never be good enough to make use of the implied parallelism in VLIW, but it might be time to revisit that now that both languages and compilation platforms have improved.