Small regression with MPIR-3.0.0

[jdemeyer]

#22493 has caused a significant regression for padic_base_leaves.py (this was discovered while investigating #23284, it is not necessarily limited to that file).

Before #22493: [142 tests, 178.75 s]

After #22493 and #23209: [142 tests, 181.61 s]

(in both cases, this was a best-out-of-10 timing but the variance is small enough that this is statistically very significant)

[dimpase]

IMHO 10% performance decrease is not too bad. As well, it's unclear whether it's limited to a particular compiler/OS/hardware combo, or not. One can also say that MPIR has added more assembly codes, and I guess one can as well find a combo that shows a performance boost.

[dimpase]

I really cannot see this as the reason not to upgrade MPIR. Consider using ODK funds to get a new CPU where new MPIR shines :-)

[jdemeyer]

Maybe we can accept a 10% performance regression, but certainly not without further investigation. The problem may be much worse than it appears to be on the surface.

[dimpase]

in any event, please attach mpir-3.0.0.p0.log of the installation where you see this slowdown.

[mmezzarobba]

Is that the same issue as #23209?

[jdemeyer]

Right, the regression is mostly explained by #23209. But even then, there remains a smaller regression of about 2%.