Defect Report: Inlining and observable behavior

The C++ standard does not say whether inlining a function may alter the
observable behavior of a program.

Example:
==========
enum CatState
{
    Dead,
    Alive
};

volatile CatState SchroedingersCat = Alive;

struct T
{
    T() {}
    T(T const&) { SchroedingersCat = Dead; }
};

inline void g(T const& p)
{
    T q(p);
}

int main()
{
    g(T());
    return 0;
}
==========
If g() is not inlined, T's copy constructor must be called when
initializing q. The copy may not be elided, since the temporary used
to initialize q is bound to the reference parameter p.

If g() is inlined, the compiler could conceivably eliminate the
single-use parameter p and transform main() to

int main()
{
    T q(T());
    return 0;
}

At this point, since the temporary is no longer bound to a reference,
the copy may be elided, and q can be value-initialized directly. This
changes the observable behavior of the program.

The C++ standard does not say anything about what transformations are
allowed when inlining a function. In particular, it doesn't say
whether inlining is allowed to change the observable behavior.

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