Floating point issues vanisch with enabled sanitizers or -O3

[svenpilz]

Hi fellow Emscripten Debuggers,

I'm looking for some ideas to debug floating point (resulting numbers are way off) issues that seem to only occur in debug builds without sanitizers. Once I build debug+sanitizers or release (-O3), everything seems to work. Those issues also only happen with Emscripten (3.1.17 at the moment), whereas GCC and Visual Studio builds don't show those problems at all.

Has someone seen something like that before or has tips on how to approach this? I already found some expression variants that change the result. Like replacing Eigen expression such as vector*a - vector*b with vector*(a-b) or vector = matrix * vector with copy=vector; copy = matrix * vectorgives different results. But that seems not directly limited to Eigen, we also see this with external libraries such as https://github.com/jbuckmccready/CavalierContours.

Thanks!

Sven