g++ and aliasing bools

[Joe Buck]

I wrote:

> But the C aliasing rules completely ignore the question of size, so you're
> bringing up a red herring.  The rules have *nothing* to do with whether we
> think that two objects have the same address!  It doesn't even come up.
> For that reason, you don't have to waste any time thinking about class
> layout.

This is true for the alias-sets computation: it depends only on types.
However, if we have more information about two accesses that allow
us to prove that they never overlap in memory, we can use that information
as well, and here the memory layout may make a difference.