RFR: 8263125: During deoptimization vectors should reassign scalarized payload after all objects are reallocated. [v2]

[Vladimir Kozlov]

On Wed, 10 Mar 2021 22:07:40 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Vladimir Kozlov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update Copyright year
>
> I vividly remember I fixed the very same problem before in Panama.
> 
> More specifically, why doesn't `VectorSupport::allocate_vector_payload` handle the case?
> 
> Handle VectorSupport::allocate_vector_payload(InstanceKlass* ik, frame* fr, RegisterMap* reg_map, ScopeValue* payload, TRAPS) {
>   if (payload->is_location() &&
>       payload->as_LocationValue()->location().type() == Location::vector) {
>     // Vector value in an aligned adjacent tuple (1, 2, 4, 8, or 16 slots).
>     Location location = payload->as_LocationValue()->location();
>     return allocate_vector_payload_helper(ik, fr, reg_map, location, THREAD); // safepoint
>   } else {
>     // Scalar-replaced boxed vector representation.
>     StackValue* value = StackValue::create_stack_value(fr, reg_map, payload);
>     return value->get_obj();
>   }
> }

Here is the order of scalarized objects in this case:
        # jdk.incubator.vector.ShortVector::rearrangeTemplate @ bci:14 (line 2117) L[0]=#ScObj0 L[1]=_ L[2]=#ScObj1 L[3]=#ScObj2 L[4]=_ L[5]=_ STK[0]=#Ptr0x00007f83a4e99850 STK[1]=#Ptr0x00007f83bd684760 STK[2]=#Ptr0x00007f83bca050f0 STK[3]=#4 STK[4]=#ScObj0 STK[5]=#ScObj1
        # ScObj0 jdk/incubator/vector/Short64Vector={ [payload :0]=rsp + #40 }
        # ScObj1 jdk/incubator/vector/Short64Vector$Short64Shuffle={ [payload :0]=#ScObj3 }
        # ScObj2 jdk/incubator/vector/Short64Vector$Short64Mask={ [payload :0]=rsp + #32 }
        # ScObj3 byte[4]={ [0]=rsp + #48 , [1]=rsp + #52 , [2]=rsp + #56 , [3]=RBP }
`ScObj1  Short64Shuffle` vector will be processed before `ScObj3 byte[4]` which it references.
VectorSupport::allocate_vector_payload() called only during `ScObj1  Short64Shuffle` reallocation when `ScObj3 byte[4]` is not reallocated yet. As result `value->get_obj()` return NULL. And that is the bug.

I forgot to say that the bug is triggered only with iterative EA I am working on. Without it `byte[]` array is not scalarized and everything works.

I also thought about calling modified `VectorSupport::allocate_vector_payload()` from `Deoptimization::reassign_fields()` to keep checks in one place but it would require more code changes then suggested fix (which is mostly asserts and debug print).

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PR: https://git.openjdk.java.net/jdk/pull/2924