> 2. In the bad old days of the x87, the FPU carried out computations on eight 80-bit registers. The problem is that whenever those registers spilled out to the stack, precision was truncated down to whatever type the language actually meant (64-bit double or 32-bit float). Because the register-spilling decision is mostly taken by the compiler, it was largely unpredictable. This resulted in code that was not reproducible, even across compiles! Since x87 was deprecated in favor of SSE/AVX, the precision of operations is always that of the type used in the code. Lower than 80-bits but much better in practice because of consistency and reproducibility.

even today it's still possible to end up with things in the x87 registers, I don't know of a compiler toggle to entirely and unequivocally disable it.