I was bit by this years ago when our test cases failed on Linux, but worked on macos. pdftotext was behaving differently (deciding to merge two lines or not) on the two platforms - both were gcc and intel at the time. When I looked at it in a debugger or tried to log the values, it magically fixed itself.

Eventually I learned about the 80-bit thing and that macos gcc was automatically adding a -ffloat-store to make == more predictable (they use a floats everywhere in the UI library). Since pdftotext was full of == comparisons, I ended up adding a -ffloat-store to the gcc command line and calling it a day.