why does AOTLib::verify_config check for UseConcMarkSweepGC?

[Christian Thalinger]

> On Jun 16, 2017, at 9:15 AM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
> What do you mean CMS does not affect code generation?
> 
> http://hg.openjdk.java.net/jdk9/dev/hotspot/file/232d93f11c49/src/share/vm/opto/graphKit.cpp#l3861 <http://hg.openjdk.java.net/jdk9/dev/hotspot/file/232d93f11c49/src/share/vm/opto/graphKit.cpp#l3861>

I was talking about Graal code generation.  Vladimir, Igor and I were talking about this offline a bit and it seems there was not particular reason.  Let me double-check this with an experiment… 

> 
> Vladimir
> 
> On 6/16/17 8:09 AM, Christian Thalinger wrote:
>> Could someone remind me, why are we checking for UseConcMarkSweepGC?
>> // Check flags
>>   verify_flag(_config->_useCompressedOops, UseCompressedOops, "UseCompressedOops");
>>   verify_flag(_config->_useCompressedClassPointers, UseCompressedClassPointers, "UseCompressedClassPointers");
>>   verify_flag(_config->_useG1GC, UseG1GC, "UseG1GC");
>>   verify_flag(_config->_useCMSGC, UseConcMarkSweepGC, "UseConcMarkSweepGC");
>> useCMSGC does not affect code generation:
>> ~/jdk9/hotspot$ ack useCMSGC
>> src/jdk.aot/share/classes/jdk.tools.jaotc.binformat/src/jdk/tools/jaotc/binformat/BinaryContainer.java
>> 303:                                   graalHotSpotVMConfig.useCMSGC,
>> src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/GraalHotSpotVMConfig.java
>> 213:    public final boolean useCMSGC= getFlag("UseConcMarkSweepGC", Boolean.class);
>> src/share/vm/aot/aotCodeHeap.cpp
>> 155:  verify_flag(_config->_useCMSGC, UseConcMarkSweepGC, "UseConcMarkSweepGC");
>> src/share/vm/aot/aotCodeHeap.hpp
>> 105:  bool _useCMSGC;
>> Is there some object-layout thing I am forgetting?

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