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SubjectRe: [PATCH 0/24] make atomic_read() behave consistently across all architectures


On Sat, 18 Aug 2007, Satyam Sharma wrote:
>
> No code does (or would do, or should do):
>
> x.counter++;
>
> on an "atomic_t x;" anyway.

That's just an example of a general problem.

No, you don't use "x.counter++". But you *do* use

if (atomic_read(&x) <= 1)

and loading into a register is stupid and pointless, when you could just
do it as a regular memory-operand to the cmp instruction.

And as far as the compiler is concerned, the problem is the 100% same:
combining operations with the volatile memop.

The fact is, a compiler that thinks that

movl mem,reg
cmpl $val,reg

is any better than

cmpl $val,mem

is just not a very good compiler. But when talking about "volatile",
that's exactly what ytou always get (and always have gotten - this is
not a regression, and I doubt gcc is alone in this).

Linus
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