On 7/1/21, scj(a)yaccman.com <scj(a)yaccman.com> wrote: Yes, this is a very well-known problem in scalar optimization in compiler engineering. It's called pointer disambiguation and is part of the more general problem of data flow analysis. As you observed, getting it wrong can lead to very subtle and hard-to-debug correctness problems. In the worst case, one has to throw out all current data flow analysis of global and currently active local variables and start over. In your example, the statement "*q = z" may end up forcing the compiler to toss out all data flow information on x and z (and maybe p and q as well). If q could possibly point to x and x is in a register, the assignment forces x to be reloaded before its next use. Ambiguous pointers prohibit a lot of important optimizations. This problem is the source of a lot of bugs in compilers that do aggressive optimizations. Fortunately a bit of knowledge of just how "q gets changed" can rescue the situation. In strongly-typed languages, for example, if x and z are different data types, we know the assignment of z through q can't affect x. We also know that the assignment can't affect x if x and z have disjoint scopes. The 'restrict' keyword in C pointer declarations was added to help mitigate this problem. Some compilers also have a command line option that allows the user to say, "I solemnly swear that I won't do this sort of thing". -Paul W.