Question about the expected behavior if JVMCI compiler is used on the jvm variant with C2 disabled

[Vladimir Kozlov]

It is https://bugs.openjdk.java.net/browse/JDK-8241779

Will work on it later.

Regards,
Vladimir

On 6/1/20 2:25 AM, Xiaohong Gong wrote:
> Hi,
> 
> Ping again! Does anyone have idea about it please? Many thanks for any help!
> 
> Thanks,
> Xiaohong Gong
> 
> From: Xiaohong Gong
> Sent: Friday, May 29, 2020 2:26 PM
> To: hotspot-compiler-dev at openjdk.java.net; hotspot-runtime-dev at openjdk.java.net
> Cc: nd <nd at arm.com>
> Subject: RE: Question about the expected behavior if JVMCI compiler is used on the jvm variant with C2 disabled
> 
> Add hotspot-runtime-dev at openjdk.java.net<mailto:hotspot-runtime-dev at openjdk.java.net> channel. Thanks!
> 
> From: Xiaohong Gong
> Sent: Wednesday, May 27, 2020 5:19 PM
> To: hotspot-compiler-dev at openjdk.java.net<mailto:hotspot-compiler-dev at openjdk.java.net>
> Cc: nd <nd at arm.com<mailto:nd at arm.com>>
> Subject: Question about the expected behavior if JVMCI compiler is used on the jvm variant with C2 disabled
> 
> Hi,
> 
> Recently we found an issue that the JVM can crash in debug mode when the JVMCI compiler is used on
> the jvm variant that C2 is disabled (Add "-with-jvm-features=-compiler2" for configuration).
> The JVM crashes with the assertion fails:
> 
> Internal Error (jdk/src/hotspot/share/compiler/compileBroker.cpp:891), pid=10824, tid=10825
> #  assert(_c2_count > 0 || _c1_count > 0) failed: No compilers?
> 
> It is obvious that the jvm cannot find a compiler since both the "_c2_count" and "_c1_count" is zero
> due to some internal issues. Since "TieredCompilation" is closed when C2 is disabled, the compile mode
> should be "interpreter+C1" by default, and it works well as expected. However,  I'm confused about the
> expected behavior if the JVMCI compiler is specified to use.
> 
> For one side, I thought it should use "interpreter+JVMCI" as the compile mode.  If so we have to fix the
> issues.  For another side, I noticed that there is a VM warning when using JVMCI compiler and disabling
> tiered compilation with normal configuration: "Disabling tiered compilation with non-native JVMCI compiler
> is not recommended". So considering that "TieredCompilation" is also closed when C2 is disabled, I thought
> it would be better to just invalid the JVMCI compiler for it.
> 
> So my question is which should be the expected behavior, choose "interpreter+JVMCI" as the compile
> mode or make it invalid to use JVMCI compiler when C2 is disabled?
> 
> It's very appreciative if I can get any opinion!
> 
> Thanks,
> Xiaohong
> 
> 
>