RFR: Fix ExtendedDTraceProbes with Shenandoah

[Roman Kennke]

Very good!

The interesting question is: is this reproducible with upstream+G1
somehow? Can you make a testcase against G1, and fix it upstream?

Also, might we have more 'hidden-ctrl-flow-bugs' lurking in our code?
We've seen some suspcious failures with C1/Level3-compiled code lately,
where embedded oops seem to point to garbled-heap-space, even before the
first GC cycle. (Shade will provide more info on that later today I
suppose.)

Roman

> Passed most tier2 with ExtendedDTraceProbes (some of tests timeout).  Of
> course, still failed CriticalNativeArgs.java with C2/traversal.
> 
> Thanks,
> 
> -Zhengyu
> 
> On 09/20/2018 04:52 PM, Roland Westrelin wrote:
>>
>> Below is a possible fix.
>>
>> Roland.
>>
>> diff --git a/src/hotspot/share/gc/shared/c1/barrierSetC1.cpp
>> b/src/hotspot/share/gc/shared/c1/barrierSetC1.cpp
>> --- a/src/hotspot/share/gc/shared/c1/barrierSetC1.cpp
>> +++ b/src/hotspot/share/gc/shared/c1/barrierSetC1.cpp
>> @@ -301,6 +301,8 @@
>>     if (gen_pre_barrier) {
>>       // We can have generate one runtime check here. Let's start with
>>       // the offset check.
>> +    LIR_Opr base_reg = gen->new_register(T_OBJECT);
>> +    __ move(base.result(), base_reg);
>>       if (gen_offset_check) {
>>         // if (offset != referent_offset) -> continue
>>         // If offset is an int then we can do the comparison with the
>> @@ -323,14 +325,14 @@
>>       if (gen_source_check) {
>>         // offset is a const and equals referent offset
>>         // if (source == null) -> continue
>> -      __ cmp(lir_cond_equal, base.result(),
>> LIR_OprFact::oopConst(NULL));
>> +      __ cmp(lir_cond_equal, base_reg, LIR_OprFact::oopConst(NULL));
>>         __ branch(lir_cond_equal, T_OBJECT, cont->label());
>>       }
>>       LIR_Opr src_klass = gen->new_register(T_METADATA);
>>       if (gen_type_check) {
>>         // We have determined that offset == referent_offset && src !=
>> null.
>>         // if (src->_klass->_reference_type == REF_NONE) -> continue
>> -      __ move(new LIR_Address(base.result(),
>> oopDesc::klass_offset_in_bytes(), T_ADDRESS), src_klass);
>> +      __ move(new LIR_Address(base_reg,
>> oopDesc::klass_offset_in_bytes(), T_ADDRESS), src_klass);
>>         LIR_Address* reference_type_addr = new LIR_Address(src_klass,
>> in_bytes(InstanceKlass::reference_type_offset()), T_BYTE);
>>         LIR_Opr reference_type = gen->new_register(T_INT);
>>         __ move(reference_type_addr, reference_type);
>>