RFR: 8311691: C2: Remove legacy code related to PostLoopMultiversioning

[Sandhya Viswanathan]

On Tue, 11 Jul 2023 09:56:51 GMT, Pengfei Li <pli at openjdk.org> wrote:

> As discussed in JDK-8308994, we are working on re-implementation of post loop vectorization and planning to refactor current SuperWord code. As nobody is using or maintaining the old implementation now, to make the refactoring work easier, we propose to remove the legacy code of the old implementation first.
> 
> This patch removes all code realted to `PostLoopMultiversioning` inside and outside SuperWord. After the removal, `SLP_extract()` in SuperWord should only work on main loops. So we also removed all `is_main_loop()` checks inside and added assertions instead.
> 
> Tested with hotspot::hotspot_all_no_apps, jdk tier1~3, langtools tier1 and 100k fuzzer tests on x86 and AArch64, no issue is found.

Looks good to me as well.

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Marked as reviewed by sviswanathan (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14824#pullrequestreview-1526807176