Why is gcc allowed to speculatively load from a struct?

Question

Example Showing the gcc Optimization and User Code that May Fault

The function \'foo\' in the snippet below will load only one of the struct members A or B; well at le

Answer 1

A postfix expression followed by the -> operator and an identifier designates a member of a structure or union object. The value is that of the named member of the object to which the first expression points

If invoking the expression P->A is well-defined, then P must actually point to an object of type struct Pair, and consequently P->B is well-defined as well.