RFR: 8319429: Resetting MXCSR flags degrades ecore [v2]

[Jatin Bhateja]

On Mon, 6 Nov 2023 23:55:59 GMT, Volodymyr Paprotski <duke at openjdk.org> wrote:

>> Improves vector rounding on ECore about 10x
>> 
>> (BEFORE) FpRoundingBenchmark.test_round_float        2048  thrpt    3  40.912 ± 0.044  ops/ms
>> (AFTER ) FpRoundingBenchmark.test_round_float        2048  thrpt    3  431.682 ± 0.727  ops/ms
>
> Volodymyr Paprotski has updated the pull request incrementally with one additional commit since the last revision:
> 
>   move option to x86-specific section

As per JVM specification section 2.8 "The floating-point instructions of the Java Virtual Machine do not throw
exceptions, trap, or otherwise signal the IEEE 754 exceptional conditions of
invalid operation, division by zero, overflow, underflow, or inexact.", thus JVM does not check these exceptions.

Your patch is always setting lower 6 bits of MXCSR on hybrid CPUs which has both E and P core, do you see any concerns if these bits are default ON for other server targets.

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

PR Comment: https://git.openjdk.org/jdk/pull/16504#issuecomment-1797673697