RFR: 8255936: "parsing found no loops but there are some" assertion failure with Shenandoah

[Roland Westrelin]

On Thu, 5 Nov 2020 08:44:03 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> This is a Shenandoah bug but the proposed fix is in shared code.
> 
> In an infinite loop, a barrier is located right after the loop head
> and above the never branch. When the barrier is expanded, control flow
> is added between the loop and the never branch. During loop
> verification the assert fires because it doesn't expect any control
> flow between the never branch and the loop head.
> 
> While it would have been nice to fix this Shenandoah issue in
> Shenandoah code, I think the cleaner fix is to preserve the invariant
> that the never branch is always right after the loop head in an
> infinite loop. In the proposed patch, this is achieved by moving all
> uses of the loop head to the never branch when it's constructed.

I rebased the change

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PR: https://git.openjdk.java.net/jdk/pull/1073