RFR (M): 8000805: JMM issue: short loads are non-atomic

[Vladimir Ivanov]

Disregard my comment about C1.

I vaguely remember I saw it fails and CR has a comment by Vladimir K. 
about C1 being also affected, but I'm not able to reproduce the problem 
anymore.

Best regards,
Vladimir Ivanov

On 10/19/12 10:39 PM, Vladimir Ivanov wrote:
> http://cr.openjdk.java.net/~vlivanov/8000805/webrev.00/
> 282 lines changed: 255 ins; 27 del; 0 mod
>
> Ideal transformations during parsing & IGVN may rematerialize loads in
> order to reify useful information (like signed/unsigned load). Such
> behavior breaks JMM - instead of a single atomic load, multiple loads
> are performed violating consistency of loaded data.
>
> The fix is to disable such transformations at all, but perform relevant
> optimizations during matching.
>
> It fixes only C2 part of problem. С1 has similar deficiency, but it'll
> be addressed separately.
>
> Testing: failing test, test for new matching rules, JPRT, CTW (x86, x64
> & sparc).
>
> Best regards,
> Vladimir Ivanov