RFR: 8252219: C2: Randomize IGVN worklist for stress testing [v3]

[Roberto Castaneda Lozano]

On Wed, 23 Sep 2020 14:14:53 GMT, Roberto Castaneda Lozano <github.com+8792647+robcasloz at openjdk.org> wrote:

>> Maybe you could add an additional HelloWorld test which only runs with your new flags to sanity check them without any
>> other flags.
>
>> Maybe you could add an additional HelloWorld test which only runs with your new flags to sanity check them without any
>> other flags.
> 
> Good idea, I just did that.

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
'StressSeed=N' option to specify the seed. If the seed is not specified, a
random one is generated. In either case, the seed is logged if 'LogCompilation'
is enabled. The new options are declared as production+diagnostic for
consistency with the existing 'StressLCM' and 'StressGCM' options.

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