That's one CVE, right? How many other vulnerabilities were caused by compiler optimizations, whether they were bugs in the compiler or allowed by the spec?

This is a different question though. A lot of UB issues are related to out-of-bounds accesses and use-after-free. But those are problematic also without optimization. The cases where optimization introduce security issues are more subtle and less common. Signed overflow related issues come to mind, but there I think UB isnow part of the solution via sanitizers (and errors related to unsigned wraparound which is defined is the far more vexing problem) and similar for dereferencing null pointers which can also easily be catched by sanitizers.