37b
Subj : Re: Memory visibility and MS Interlocked instructions
To   : comp.programming.threads
From : Peter Dimov
Date : Thu Aug 25 2005 03:35 pm

Alexander Terekhov wrote:
> Peter Dimov wrote:
> [...]
> > Can you give approximate PPC translation for the expression
> >
> > fValueHasBeenComputed.load(msync::cchlb_true)
> >
> > assuming that the compiler is not smart/atomics-aware and can't just
> > insert the isync after the 'if'? (IOW, it can't analyze and optimize
> > the 'load' in context... a library implementation, for example.)
>
>   lwz r4,0(r3) #load shared data
>   cmpw r4,r4 #set CR0 to "equal"
>   bne- $-8 #branch never taken
> ---
>
> and just add isync after "branch never taken".

That's what I thought. In this case there is no difference between
cchlb_true and cchlb (and ccacq, and even plain acq because of the fake
control dependency.)

.

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