Re: volatile semantics

[Paul Koning <pkoning@equallogic.com>]

>>>>> "Dale" == Dale Johannesen <dalej@apple.com> writes:

 Dale> On May 4, 2005, at 5:06 AM, Gabriel Dos Reis wrote:

 >> Andrew Haley <aph@redhat.com> writes:
 >> 
 >> | Nathan Sidwell writes: | > Dale Johannesen wrote:
 >> |  >
 >> | > > And we don't have to document the behavior at all; it is not
 >> documented | > > now.  | > I disagree.  It's not documented
 >> explicitly in gcc now, because it is doing | > what the std
 >> permits, and so documented there. We should document either
 >> |  >
 >> | > a) that current gcc is not breaking the std, and Mike's
 >> example is invalid | > code, if one expects a volatile read.  This
 >> would be a FAQ like thing.

 Dale> Both behaviors are standard-compliant.  Treating a reference as
 Dale> volatile when you don't have to just means strictly following
 Dale> the rules of the abstract machine; it can never break anything.

 >> I vote for (a).
 >> 
 >> [...]
 >> 
 >> | This is a bad extension to gcc and will cause much trouble, just
 >> like | the old guarantee to preserve empty loops.

 Dale> I see a difference between a documented extension, and quietly
 Dale> choosing from among standard-compliant behaviors the one which
 Dale> is most convenient for users.

I agree, but I would put it more strongly -- choose the interpretation
which (a) satisfies the principle of least astonishment, (b) matches
previous version behavior, and (c) will keep existing user code
working rather than breaking it in hard to debug ways.

	paul