> From: David Jencks [mailto:david_jen...@yahoo.com.INVALID]
> Subject: Re: RV-Predict bugs
> I have been having a hard time believing the reordering claims, but finally I
> went to Jeremy's
> blog post. To recap, he says
> if (hash == 0) {
> int h = //compute hash
> hash = h;
> }
> return hash;
> can be reordered to
> r1 = hash;
> if (hash == 0) {
> r1 = hash = // calculate hash
> }
> return r1;
> Obviously this last version is susceptible to returning 0.
> It looks to me like the 2nd version is not a reordering of the java
> statements of the first version.
Correct; it's different logic, and thus a bit of a red herring. It introduces
a timing window not present in the original code; it's not an example of a
speculative read.
- Chuck
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