RFR(S): 8231291: C2: loop opts before EA should maximally unroll loops

[Vladimir Ivanov]


>> I understand that the change you have is enough to avoid the problematic 
>> case in GraphKit::must_be_not_null(). What I'd like to get rid of is the 
>> need for a correctness check to ensure that HaltNode can't go away. It's 
>> error-prone and can eventually get out of sync.
> 
> Fair enough. Then why not always enqueue the root node for igvn at the
> end of parsing?

Sounds good. FTR I’m fine with both options. But unconditionally registering RootNode for IGVN looks like a simpler and cleaner solution.

> 
>> Also, I'd like the bug to be handled separately (from 8231291). It'll 
>> simplify possible backporting: as I see from the history, the 
>> problematic code (JDK-8176506) was introduced in 10 and it may show up 
>> in 11u eventually.
> 
> You're right. That's cleaner. I'll send new webrevs.

Thanks!

Best regards,
Vladimir Ivanov

> 
> Roland.
>