[15] RFR(S): 8244724: CTW: C2 compilation fails with "Live Node limit exceeded limit"

[Vladimir Kozlov]

You don't need to use 'C->' in Compile::Optimize() method:

DEBUG_ONLY(C->set_phase_optimize_finished();)

Yes, remove all nodes limit checks after optimization phase.

Thanks,
Vladimir

On 6/26/20 7:38 AM, Christian Hagedorn wrote:
> Hi
> 
> Please review the following patch:
> https://bugs.openjdk.java.net/browse/JDK-8244724
> http://cr.openjdk.java.net/~chagedorn/8244724/webrev.01/
> 
> The testcase contains many string concatinations. These are compiled by javac with -XDstringConcat=inline which creates 
> a lot of StringBuilder objects and calls. As a result, we get a huge graph and eventually hit the live node limit assert 
> during code generation when trying to create new nodes - either during PhaseCFG::build_cfg() or later in 
> PhaseCFG::global_code_motion().
> 
> We could try to introduce estimates for them to bailout but that appears to be difficult to get right without being too 
> pessimistic about it. But we need to be in order to avoid hitting the assert again by just modifying the testcase.
> 
> Therefore, my suggestion is to completely skip the assert once the optimization phase is finished as we should not 
> strictly care about the node limit anymore at this point in time and it does not really provide much help for finding bugs.
> 
> A question remains, though, if we should also get rid of the remaining live node limit bailout checks in 
> Compile::Code_Gen() like [1] as it appears to be a waste to go through all the optimization in the optimization phase to 
> then bailout while generating code based only on the live node limit itself. What do you think about that?
> 
> I also updated "<" into "<=" in the live node limit assert because we should be allowed to reach the limit but not go 
> beyond.
> 
> Thank you!
> 
> Best regards,
> Christian
> 
> 
> [1] http://hg.openjdk.java.net/jdk/jdk/file/8fd3e34e8379/src/hotspot/share/opto/coalesce.cpp#l236