Not all CPUs behave badly when handling underflows, denormals or other exceptional cases. On some CPUs the penalties for exceptional cases are negligible (e.g.

Not all CPUs behave badly when handling underflows, denormals or other exceptional cases. On some CPUs the penalties for exceptional cases are negligible (e.g. on AMD Zen), so it is impossible for any SPEC benchmark to get a 30% speedup when ignoring underflows. There are also bad CPU models, which have a microprogrammed handling of the exceptional cases, which can add e.g. a penalty of somewhat more than one hundred CPU cycles for each underflow, which is very similar to the penalty for a load from the main memory (which misses the caches). If one of the SPEC benchmarks has so many underflows that on a bad CPU model it can be sped up by 30% when ignoring the underflows, then it is pretty much guaranteed that when the underflows are ignored the results computed by that benchmark are erroneous. Cheating at the SPEC benchmark by ignoring the underflows could be easily avoided by changing the benchmarking rules, by providing a file with the valid results and by not accepting any benchmark claims where the results do not match those known to be good. You can cheat at any SPEC benchmark with bogus compiler options, if there is no constraint on the compiled program to be correct. For instance you could make a compilation option that deletes 90% of the generated machine code, resulting in a 10 times faster benchmark program. For some reason, the compiler writers that handle the generation of code for floating-point operations feel that they are licensed to generate incorrect code, even when similarly incorrect code would be rejected in other contexts. The fact that the floating-point operations are inexact, so they are accompanied by some inherent errors, does not give the right to a compiler writer or library writer to introduce arbitrary errors in the computations. The reason why a standard exists is precisely for guaranteeing that the errors are bounded and you can predict their effects.