And to be clear, there are still limitations. It can't say if any value you pass into a function that is not part of the current compilation is safe. For somewhat obvious reasons.
But for a large large class of bugs, using advanced tooling can go a long way. As evidenced by the power of the advanced tooling new languages bring into the compilers. :)
It can tell you that, "if this line is reached, and it was called from this path (with evidence on how this could happen), it will dereference a null." It is not saying that "running this program will guarantee give you a null dereference."
The halting problem is more in line with "this program will terminate on any possible inputs", which is more expansive. It is trivial to say that you can prove some programs won't terminate on a particular input. Question is if you can do it for all inputs, no?
But I don't think the Op was claiming it was possible to do this perfectly, just possible to write very useful tools. You will always have either flase positives or false negatives (or I suppose inputs where you just hang).
Turing completeness is the bane of static analysis, but that doesn't make it a fruitless endeavor.
[1] Recent headline 'Phantom Code Paths Found Harmful'