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    SubjectRe: [patch] spinlocks: remove 'volatile'

    > Btw, I think that the whole standard definition of "volatile" is pretty
    > weak and useless. The standard could be improved, and a way to improve the
    > definition of volatile would actually be to say something like
    > "volatile" implies that the access to that entity can alias with
    > any other access.
    > That's actually a lot simpler for a compiler writer (a C compiler already
    > has to know about the notion of data aliasing), and gives a lot more
    > useful (and strict) semantics to the whole concept.
    > So to look at the previous example of
    > extern int a;
    > extern int volatile b;
    > void testfn(void)
    > {
    > a++;
    > b++;
    > }
    > _my_ definition of "volatile" is actually totally unambiguous, and not
    > just simpler than the current standard, it is also stronger. It would make
    > it clearly invalid to read the value of "b" until the value of "a" has
    > been written, because (by my definition), "b" may actually alias the value
    > of "a", so you clearly cannot read "b" until "a" has been updated.
    > In contrast, the current C standard definition of "volatile" is not only
    > cumbersome and inconvenient, it's also badly defined when it comes to
    > accesses to _other_ data, making it clearly less useful.
    > I personally think that my simpler definition of volatile is actually a
    > perfectly valid implementation of the current definition of volatile, and
    > I suggested it to some gcc people as a better way to handle "volatile"
    > inside gcc while still being standards-conforming (ie the "can alias
    > anything" thing is not just clearer and simpler, it's strictly a subset of
    > what the C standard allows, meaning that I think you can adopt my
    > definition _without_ breaking any old programs or standards).

    Are you sure?

    volatile int a; a=1; a=2;

    ...under old definition, there's nothing to optimize but AFAICT, your
    definition allows optimizing out a=1.

    Thanks for all the (sleeping) penguins.
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