RFR (XS) 8223450: Disable Shenandoah C2 barriers verification for x86_32

[Roman Kennke]

Looks good, thanks!

Roman


> Bug:
>    https://bugs.openjdk.java.net/browse/JDK-8223450
> 
> Shenandoah C2 barrier verification is disabled when unusual barrier configuration is requested.
> However, that only takes care of options provided from the command line (as our tests assert). For
> the configuration that disables barriers implicitly, e.g. x86_32, this is not enough, and tests fail
> with false negatives. We need to disable C2 barriers verification explicitly there.
> 
> Fix:
> 
> diff -r 1c3292907e4b src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp
> --- a/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp   Tue May 07 12:19:28 2019 +0200
> +++ b/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp   Tue May 07 12:23:15 2019 +0200
> @@ -48,10 +48,12 @@
>     FLAG_SET_DEFAULT(ShenandoahLoadRefBarrier,         false);
>     FLAG_SET_DEFAULT(ShenandoahKeepAliveBarrier,       false);
>     FLAG_SET_DEFAULT(ShenandoahStoreValEnqueueBarrier, false);
>     FLAG_SET_DEFAULT(ShenandoahCASBarrier,             false);
>     FLAG_SET_DEFAULT(ShenandoahCloneBarrier,           false);
> +
> +  FLAG_SET_DEFAULT(ShenandoahVerifyOptoBarriers,     false);
>   #endif
> 
>   #ifdef _LP64
>     // The optimized ObjArrayChunkedTask takes some bits away from the full 64 addressable
>     // bits, fail if we ever attempt to address more than we can. Only valid on 64bit.
> 
> Testing: hotspot_gc_shenandoah
>