Lots of failing tests on arm64 Macs due to Clang default of `-ffp-contract=on`

Hi all,

Building VTK master on my Intel Mac results in only 1 test failure. But on arm64 Macs, there are about 15.

You can see details here:


I debugged them, and found at least 2 were due to very tight numerical precision expectations, and created MRs:


I then had some deja vu, and remembered how Clang 14 changed to default to -ffp-contract=on and how this caused numerical differences in our own code, more so on arm64 than x86_64. So I tried building again with -ffp-model=strict and now 13 of 15 pass.

Since this is clang’s default now (on almost all platforms), what should we do about this?

Require -ffp-model=strict? Loosen the strictness of the tests?