RFR: 8260637: Shenandoah: assert(_base == Tuple) failure during C2 compilation

[Roland Westrelin]

On Thu, 4 Feb 2021 08:34:04 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> Another shenandoah bug with a fix in shared code.
> 
> LRBRightAfterMemBar.test2() has 2 allocations that are non escaping
> but non scalarizable. As a result, the null check for a3.f is
> optimized out but the CastPP is left in the graph. That CastPP becomes
> control dependent on the o2 == null check which is later hoisted out
> of the loop. The CastPP is then right after the membar of the barrier = 0x42
> volatile access but with an out of loop control. Because the node is
> considered pinned by loopopts, it is assigned the membar as
> control. The input of the CastPP is a shenandoah barrier that's
> sandwiched between the membar and the CastPP and so expanded right
> after the membar (that is between the membar and its control
> projection). That causes the crash. I don't think cast nodes need to
> be pinned so I propose that as a fix.

Anyone for this (simple) change to shared c2 code?

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PR: https://git.openjdk.java.net/jdk/pull/2400