RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v7]

[John R Rose]

On Tue, 25 Oct 2022 23:13:08 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> …very modest impact while still being able to catch important types of MXCSR corruption. I fully support having it turned on by default for JNI calls.

I guess I agree.  With the clever test for the bad mode Java cares about, the overhead is small compared to an empty JNI call, and very small compared to any normally non-empty JNI call.

Now I'm curious:  What's this magic code?  Does it multiply a couple of well-chosen constants and test for zero?

I said "I guess" because I'm not clear on (a) the benefit of adding that nanosecond (other than preserving denorms against a rare system fault), nor on (b) what are the remaining faults not checked for, but which a more expensive MSR spill/restore would fix.

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PR: https://git.openjdk.org/jdk/pull/10661