[jhj]

The original sin here is that original 1980s designs carry over: the processor retains FP unit state, rather than each instruction indicating what subnormal flush mode (or rounding mode or whatever) one wishes to use with no retained FP unit state. See also: the IEEE FP exception design (e.g., signaling NaNs) causing havoc with SIMD, deep pipelining, out-of-order execution etc.