RFR: 8330157: C2: Add a stress flag for bailouts [v7]

[Daniel Skantz]

On Mon, 1 Jul 2024 07:04:25 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> test/hotspot/jtreg/testlibrary/ctw/src/sun/hotspot/tools/ctw/CtwRunner.java line 307:
>> 
>>> 305:                 "-XX:+StressIncrementalInlining",
>>> 306:                 "-XX:+StressBailout",
>>> 307:                 "-XX:StressBailoutProbability=100_000_000",
>> 
>> This value allows us to compile any given method with high probability.
>> The largest number of `failing()` checks that I have seen so far is 10**6.
>> 
>> I am not sure if this could hide an infinite compilation due to an unrelated bug.
>> If we want to guard against edge cases, we could do an additional check against
>> the stress seed, for example disabling this stress mode if `!(_stress_seed % 10)`.
>
> Or you somehow randomly enable/disable the `StressBailout` flag? Stuffing too much special-logic into the internals could be quite confusing for the flag-user.

We can do that perhaps in `initialize_stress_seed` and rename the method, but the `StressBailoutMean` interface could still become less intuitive.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19646#discussion_r1660801626