RFR: 8285301: C2: assert(!requires_atomic_access) failed: can't ensure atomicity

[Dean Long]

On Wed, 27 Apr 2022 10:25:36 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> We hit asserts in `BarrierSetC2::load_at_resolved` and `BarrierSetC2::store_at_resolved` when running with `-XX:+AlwaysAtomicAccesses` because the corresponding code paths have not been implemented yet. Although the assert triggers on all platforms, it only affects long and double accesses on 32-bit systems (everything else is atomic anyway).
> 
> I moved the `requires_atomic_access` logic into `LoadNode::make` and `StoreNode::make` and refactored related code.
> 
> I noticed that `LoadNode::convert_to_reinterpret_load` and `StoreNode::convert_to_reinterpret_store` did not properly check for `requires_atomic_access` and fixed that as well.
> 
> I'm currently running all tests with `-XX:+AlwaysAtomicAccesses`.
> 
> Thanks,
> Tobias

The new TestAlwaysAtomicAccesses test seems suspiciously simple.  I guess the idea is to catch issues during startup with -Xcomp.  A comment saying that could prevent someone from thinking the test does nothing.

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PR: https://git.openjdk.java.net/jdk/pull/8422