Mark Mitchell wrote:
Will the UK committee open a DR for this? Or, would you care to send mail to Steve Adamczyk about it?
this can be done. I shall wait until the minutes have been written up.
Excellent.
The observation was made that if A is non-POD, one cannot play offsetof tricks to get from A::a to A::b, so the optimization is safe on non-PODs. (Of course one would have to prove the address of 'v' did not escape, so I guess the ctor and dtor would need to be trivial or visible.)
I argued last week that this was not in fact true, in that you can do:
ptrdiff_t x = &v.b - &v.a;
and then use that instead of "offsetof (Foo, b) - offsetof (Foo, a)".
Does not '&v.b - &v.a' cause the address to 'escape', and therefore lock down the structure? If it doesn't, how hard would it be to make that DTRT?
It wouldn't look like escape to (at least some compilers') optimizers if, say, the front end folded it to a constant. So, I'm not sure how to express what constitutes escape.
-- Mark Mitchell CodeSourcery, LLC [EMAIL PROTECTED] (916) 791-8304
