What I'm saying is that speculative execution without modifying the cache is safe from a Spectre reading arbitrary memory, the main concern. So start from ther

What I'm saying is that speculative execution without modifying the cache is safe from a Spectre reading arbitrary memory, the main concern. So start from there. That's not a terrible starting position, with all of today's predictive logic and speculative pipelines working at full speed on the fastest codes and partially working as codes use more uncached memory accesses. Then you add back in things like speculatively prefetching code and global variables (addresses hardcoded in the instruction not calculated) and you're nearly back to 2017 performance. The problem is widespread and severe, but we're not going back to some dark ages of computing.