RFR: 8346989: Deoptimization and re-compilation cycle with C2 compiled code

[Emanuel Peter]

On Thu, 6 Mar 2025 07:16:40 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> `Math.*Exact` intrinsics can cause many deopt when used repeatedly with problematic arguments.
>> This fix proposes not to rely on intrinsics after `too_many_traps()` has been reached.
>> 
>> Benchmark show that this issue affects every Math.*Exact functions. And this fix improve them all.
>> 
>> tl;dr:
>> - C1: no problem, no change
>> - C2:
>>   - with intrinsics:
>>     - with overflow: clear improvement. Was way worse than C1, now is similar (~4s => ~600ms)
>>     - without overflow: no problem, no change
>>   - without intrinsics: no problem, no change
>> 
>> Before the fix:
>> 
>> Benchmark                                           (SIZE)  Mode  Cnt     Score      Error  Units
>> MathExact.C1_1.loopAddIInBounds                    1000000  avgt    3     1.272 ±    0.048  ms/op
>> MathExact.C1_1.loopAddIOverflow                    1000000  avgt    3   641.917 ±   58.238  ms/op
>> MathExact.C1_1.loopAddLInBounds                    1000000  avgt    3     1.402 ±    0.842  ms/op
>> MathExact.C1_1.loopAddLOverflow                    1000000  avgt    3   671.013 ±  229.425  ms/op
>> MathExact.C1_1.loopDecrementIInBounds              1000000  avgt    3     3.722 ±   22.244  ms/op
>> MathExact.C1_1.loopDecrementIOverflow              1000000  avgt    3   653.341 ±  279.003  ms/op
>> MathExact.C1_1.loopDecrementLInBounds              1000000  avgt    3     2.525 ±    0.810  ms/op
>> MathExact.C1_1.loopDecrementLOverflow              1000000  avgt    3   656.750 ±  141.792  ms/op
>> MathExact.C1_1.loopIncrementIInBounds              1000000  avgt    3     4.621 ±   12.822  ms/op
>> MathExact.C1_1.loopIncrementIOverflow              1000000  avgt    3   651.608 ±  274.396  ms/op
>> MathExact.C1_1.loopIncrementLInBounds              1000000  avgt    3     2.576 ±    3.316  ms/op
>> MathExact.C1_1.loopIncrementLOverflow              1000000  avgt    3   662.216 ±   71.879  ms/op
>> MathExact.C1_1.loopMultiplyIInBounds               1000000  avgt    3     1.402 ±    0.587  ms/op
>> MathExact.C1_1.loopMultiplyIOverflow               1000000  avgt    3   615.836 ±  252.137  ms/op
>> MathExact.C1_1.loopMultiplyLInBounds               1000000  avgt    3     2.906 ±    5.718  ms/op
>> MathExact.C1_1.loopMultiplyLOverflow               1000000  avgt    3   655.576 ±  147.432  ms/op
>> MathExact.C1_1.loopNegateIInBounds                 1000000  avgt    3     2.023 ±    0.027  ms/op
>> MathExact.C1_1.loopNegateIOverflow                 1000000  avgt    3   639.136 ±   30.841  ms/op
>> MathExact.C1_1.loop...
>
> The benchmark generally looks good to me, I only have some minor suggestions ;)

> Is it worth inlining at all? @eme64 wondered, so I tried with this code:

You ask this in the PR description. I think I was not thinking about `inlining` but rather using the `intrinsic`. How much speedup does the intrinsic really deliver? Is it really better than pure Java?

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PR Comment: https://git.openjdk.org/jdk/pull/23916#issuecomment-2703015476