RFR: 8227083: ZGC: C2: Generates on_weak barrier for WeakCompareAndSwap

[Nils Eliasson]

Looks good!

// Nils

On 2019-07-02 14:52, Stefan Karlsson wrote:
> Hi all,
>
> Please review this patch to fix so that we generate an on_strong load 
> barrier for WeakCompareAndSwap.
>
> http://cr.openjdk.java.net/~stefank/8227083/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8227083
>
> ErikÖ spotted this problem when we were looking into the bug for 
> JDK-8225770, where C2 also generated the wrong kind of barrier.
>
> In this bug there was a mix-up of terms, the weak nature of 
> WeakCompareAndSwap is unrelated to the on_weak property of some load 
> barriers. The barrier in this code path should be using the normal, 
> on_strong, load barries.
>
> The verification code in JDK-8227085 did catch this bug, as expected, 
> and with the fix for this bug we don't fail in the verification code 
> anymore.
>
> Tested with tier 1-7.
>
> Thanks,
> StefanK