RFR: 8346989: C2: deoptimization and re-compilation cycle with Math.*Exact in case of frequent overflow [v7]
Marc Chevalier
mchevalier at openjdk.org
Thu Apr 3 13:01:15 UTC 2025
> `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.loopNegateLInBounds 1000000 avgt 3 2.422 ± 3.59...
Marc Chevalier has updated the pull request incrementally with one additional commit since the last revision:
Remove useless flags in tests
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/23916/files
- new: https://git.openjdk.org/jdk/pull/23916/files/238b129d..e7c8f3e0
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=23916&range=06
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=23916&range=05-06
Stats: 9 lines in 1 file changed: 0 ins; 0 del; 9 mod
Patch: https://git.openjdk.org/jdk/pull/23916.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/23916/head:pull/23916
PR: https://git.openjdk.org/jdk/pull/23916
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