confusing code....whats the point of this construct ?

[Valdis.Kletnieks at vt.edu]

On Wed, 11 Mar 2015 18:37:32 -0000, Jeff Haran said:

> I don't understand the problem here. The caller passes in a condition to be
> evaluated in a loop. Many times that condition is quite simple (e.g. a counter
> being non-zero). If it was a function the caller would have to pass in a
> pointer to a function that does the evaluation, as in:

We do pointers to callback functions all the time.  We try *really* hard
to avoid anonymous lambda functions (which is basically what we have here).

The problem here is that there's about 3 zillion ways to screw up the inline
version, starting with the compiler optimizing the control variable into a
hoisted load outside the loop and causing the test to always fail - note that
the macro does *not* use any barriers or volatile or anything like that.

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