In my experience, -ffast-math has become vastly more useful over the last 10-15 years. I suppose this was a somewhat reasonable discussion to have in 2001, when

In my experience, -ffast-math has become vastly more useful over the last 10-15 years. I suppose this was a somewhat reasonable discussion to have in 2001, when most performance critical code still heavily relied on hand-optimized assembly, but nowadays -ffast-math is often the only reasonably convenient way to get compilers to autovectorize code properly, use FMA instructions, etc. I have production code that literally runs 4x faster purely by adding -ffast-math due to autovectorization (and subsequent ILP and other improvements).