RFR: 8252219: C2: Randomize IGVN worklist for stress testing

[Roberto Castañeda Lozano]

On Fri, 18 Sep 2020 10:29:48 GMT, Roberto Castañeda Lozano <github.com+8792647+robcasloz at openjdk.org> wrote:

>> Add `StressIGVN` option to let C2 randomize IGVN worklist order. When enabled, the worklist is shuffled before each
>> main run of the IGVN loop. Also add `GenerateStressSeed' and 'StressSeed=N` options to randomly generate or specify the
>> seed. In either case, the seed is logged if `LogCompilation` is enabled.  The generation or specification of seeds also
>> affects the randomization triggered by `StressLCM` and `StressGCM`. The new options are declared as
>> production+diagnostic for consistency with these existing options.
>
> Add 'StressIGVN' option to let C2 randomize IGVN worklist order. When enabled,
> the worklist is shuffled before each main run of the IGVN loop. Also add
> 'GenerateStressSeed' and 'StressSeed=N' options to randomly generate or specify
> the seed. In either case, the seed is logged if 'LogCompilation' is enabled.
>     
> The generation or specification of seeds also affects the randomization
> triggered by 'StressLCM' and 'StressGCM'. The new options are declared as
> production+diagnostic for consistency with these existing options.

Reverted to "draft mode", as I just realized the design is not repeatable since it relies on global PRNG state.

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PR: https://git.openjdk.java.net/jdk/pull/242