Regarding 8033626: C2: Merging exception state: reexecute=true vs reexecute=false

[Vladimir Kozlov]

PredictedIntrinsicGenerator was added to have a general predicate. For 
example, AES crypto predicate checks klass of an object pointed by a 
field. PredictedCallGenerator checks klass of method's holder only.

Both cases would have the same problem with reexecute. Using 
PredictedIntrinsicGenerator will not help you.

But you should not have this problem at the merge point, because 
reexecute should be reset back after intrinsic is generated:

   { PreserveReexecuteState preexecs(this);
     jvms()->set_should_reexecute(true);

It is strange that it is still true after PreserveReexecuteState destructor.

Vladimir K

On 5/28/14 9:37 AM, Vladimir Ivanov wrote:
> Hi,
>
> I'm looking at 8033626 [1]:
> "assert(ex_map->jvms()->same_calls_as(_exceptions->jvms())) failed: all
> collected exceptions must come from the same place".
>
> 8014447 [2] introduced new code shape for virtual intrinsifiable methods
> (Object::hashCode & Object::clone): "invokevirtual Object.clone()" can
> be represented as a PredictedCallGenerator with LibraryIntrinsic on fast
> path and VirtualCallGenerator on slow path.
>
> The problem arises for Object::clone, because for OOM case intrinsified
> version requires reexecution (reexecute=true), but slow path (virtual
> dispatch) doesn't (reexecute=false). Further attempt to finish the
> diamond and merge 2 exception states fires the assertion.
>
> So, I have 2 questions:
>    (1) I don't see any way to merge reexecute=true & reexecute=false
> states, so both branches should have the same reexecute status. Am I
> missing something?
>
>    (2) Does PredictedCallGenerator actually support such shape
> (intrinsic on fast path)? There are 2 call generators:
> PredictedIntrinsicGenerator & PredictedCallGenerator. What's the
> difference?
>
> I see there's a way to customize predicate in
> LibraryCallKit::try_to_predicate() for PredictedIntrinsicGenerator, but
> is it the only reason why PredictedIntrinsicGenerator was introduced?
>
> Best regards,
> Vladimir Ivanov
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8033626
>
> [2] https://bugs.openjdk.java.net/browse/JDK-8014447
>      "Object.hashCode intrinsic breaks inline caches"