e.g. if the value you're interested in is being passed to / returned from a function then inspecting it around the call / return site should have the value available.
Pass various arguments to `backtrace` rather than just relying the default. Chances are it will have some non-optimized-out variables, which you can use to figure out what's going on.
Use `info registers` and see what looks like a pointer, then cast it to a type you suspect it is. Note that this can be done for any stack frame.
In that case, the code did become pretty hard to debug due to the extensive inlining and reordering it had allowed. Unfortunate because the only reason such functions exist is to make the structure of the code more apparent!
Maybe that's an exception (and / or maybe it's easier with C than for C++).
Maybe the less is that it's still always worth trying function call boundaries, in case the compiler has been conservative!