My guess is that the problem isn't with this line per-se, but that some of those components in that string of dots are unions, that the program is doing one of

My guess is that the problem isn't with this line per-se, but that some of those components in that string of dots are unions, that the program is doing one of those things with unions that have always officially been undefined behavior (so older standards aren't going to help) but which used to happen to work reliably, and that that's tripping up the modern compilers. I'd look at the types of hash_ptr, hash_ptr.parm, hash_ptr.parm.v, and hash_ptr.parm.v.p; I'd try building without optimizations (-O0) and see if that changes anything; and as others have said I'd try pulling it up in a debugger so I can poke things.