[lworld] RFR: 8264414: [lworld] [AArch64] TestBufferTearing.java fails with C1

[Nick Gasson]

On Thu, 1 Apr 2021 12:52:07 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> We see failures like this on AArch64 when MyValue.incrementAndCheck() is
>> compiled with C1:
>> 
>>   java.lang.RuntimeException: Inconsistent field values: expected 0 to equal 675128
>>         at jdk.test.lib.Asserts.fail(Asserts.java:594)
>>         at jdk.test.lib.Asserts.assertEquals(Asserts.java:205)
>>         at jdk.test.lib.Asserts.assertEQ(Asserts.java:178)
>>         at compiler.valhalla.inlinetypes.MyValue.incrementAndCheck(TestBufferTearing.java:81)
>>         at compiler.valhalla.inlinetypes.TestBufferTearing$Runner.run(TestBufferTearing.java:124)
>> 
>> The barrier that is usually inserted on return from a method that wrote
>> final fields should be sufficient to prevent another thread seeing the
>> zero-initialised intermediate state.  However this barrier isn't
>> inserted at the moment because method()->is_object_constructor() is
>> false for primitive class constructors.
>> 
>> C2 has a similar guard around the memory barrier in Parse::do_exits().
>> I'm not sure if that needs amending as well but I've not seen any
>> failures due to it.
>
> Hi Nick,
> 
> I think we also need a barrier in `GraphBuilder::access_field` when loading from a flattened field and in `GraphBuilder::load_indexed` (the initialization code is emitted in `LIRGenerator::access_flattened_array`) when loading from a flattened array.
> 
> It would be good to have tests that triggers this.
> 
> Best regards,
> Tobias

@TobiHartmann I've added the two missing membars and a test.

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PR: https://git.openjdk.java.net/valhalla/pull/376