Whenever I do cabal sdist on one of my projects, I get this warning: Distribution quality warnings: 'ghc-options: -O2' is rarely needed. Check that it is giving a real benefit and not just imposing longer compile times on your users. This finally got me curious and I did a nofib run to compare -O to -O2. The results are below (this is with the current HEAD). Is there a real-world example of -O2 causing significantly longer compile times without providing a real benefit? If not, would it perhaps make sense for Cabal to use -O2 by default or even for GHC to make the two flags equivalent? Roman NoFib Results -------------------------------------------------------------------------------- Program Size Allocs Runtime Elapsed -------------------------------------------------------------------------------- anna +2.5% -0.2% 0.08 0.11 ansi +0.0% +0.0% 0.00 0.01 atom +0.0% +0.0% 0.20 +0.0% awards +0.0% +0.0% 0.00 0.01 banner +0.0% +0.0% 0.00 0.01 bernouilli +0.0% +0.0% +0.0% +0.5% boyer +0.0% -0.3% 0.03 0.04 boyer2 +0.2% +0.0% 0.00 0.01 bspt +0.4% +0.0% 0.00 0.02 cacheprof +0.6% +0.0% +0.0% +0.0% calendar +0.2% +0.1% 0.00 0.01 cichelli +0.0% -0.0% 0.07 0.08 circsim +0.2% -0.0% -1.4% +0.3% clausify +0.2% -6.8% 0.03 0.04 comp_lab_zift +0.8% +0.7% 0.17 0.19 compress +0.0% +0.0% 0.14 0.16 compress2 +2.3% -1.3% 0.14 0.17 constraints +0.0% +0.0% -0.4% -0.0% cryptarithm1 +0.0% +0.0% +0.0% -0.3% cryptarithm2 +0.0% -4.7% 0.01 0.02 cse +0.0% +0.0% 0.00 0.01 eliza +0.0% +0.0% 0.00 0.01 event +0.2% +1.5% 0.14 0.16 exp3_8 +0.0% +0.0% 0.10 0.11 expert +0.4% +0.4% 0.00 0.01 fem +0.5% +1.0% 0.02 0.02 fft +0.2% -1.6% 0.03 0.04 fft2 +0.2% +0.0% 0.06 0.07 fibheaps +0.2% +0.4% 0.03 0.04 fish +0.0% +0.0% 0.01 0.03 fluid +2.1% -1.9% 0.01 0.02 fulsom +0.2% +0.0% +0.0% -0.5% gamteb +0.7% -2.1% 0.07 0.09 gcd +0.0% -1.7% 0.02 0.02 gen_regexps +0.0% +0.0% 0.00 0.01 genfft +0.0% -0.3% 0.03 0.03 gg +0.5% -0.8% 0.01 0.02 grep +0.2% +0.0% 0.00 0.01 hidden +0.3% +0.0% -3.2% -3.5% hpg +0.2% +0.0% 0.14 +0.6% ida +0.5% -0.7% 0.07 0.08 infer +0.0% +0.0% 0.04 0.05 integer +0.0% +0.0% +0.0% +0.0% integrate +0.0% +0.0% +0.0% +0.0% knights +0.7% -13.4% 0.00 0.01 lcss +0.0% -0.0% -0.8% -0.7% life +0.0% +0.0% 0.20 -1.0% lift +0.2% +3.6% 0.00 0.01 listcompr +0.0% +0.0% 0.09 0.12 listcopy +0.0% -0.0% 0.10 0.13 maillist +0.0% -0.2% 0.05 +0.2% mandel +0.0% +0.0% 0.07 0.09 mandel2 +0.2% -67.2% 0.00 0.00 minimax +0.0% +0.4% 0.00 0.01 mkhprog +0.0% +0.0% 0.00 0.01 multiplier +0.0% +0.0% 0.09 0.11 nucleic2 +0.0% +0.0% 0.06 0.07 para +0.9% +0.5% +6.4% +5.5% paraffins +0.4% +0.2% 0.07 0.10 parser +0.5% +0.3% 0.03 0.04 parstof +0.2% -2.5% 0.00 0.01 pic +0.4% -0.8% 0.00 0.02 power +0.4% +0.0% +0.0% +0.8% pretty +0.2% -2.9% 0.00 0.01 primes +0.0% +0.0% 0.05 0.06 primetest +0.2% +0.0% +0.0% +0.6% prolog +0.2% -0.9% 0.00 0.01 puzzle +0.0% +0.0% 0.14 0.16 queens +0.0% -72.0% 0.01 0.02 reptile +0.2% +0.0% 0.01 0.02 rewrite +0.2% +0.0% 0.01 0.02 rfib +0.0% +0.0% 0.04 0.05 rsa +0.0% +0.0% 0.06 0.07 scc +0.0% +0.0% 0.00 0.01 sched +0.2% +0.6% 0.02 0.03 scs +0.8% -0.4% +0.0% +1.4% simple +0.2% +0.0% +0.0% +0.0% solid +0.0% -0.0% 0.11 0.13 sorting +0.2% +0.0% 0.00 0.01 sphere +0.0% +0.5% 0.08 0.09 symalg +0.5% -0.0% 0.03 0.04 tak +0.0% +0.0% 0.01 0.02 transform +0.6% -0.0% +0.0% +0.7% treejoin +0.2% -2.0% 0.20 +3.5% typecheck +0.0% +0.3% 0.19 +0.0% veritas +1.0% -0.3% 0.00 0.01 wang +0.0% -1.0% 0.07 0.09 wave4main +0.0% +0.0% +3.7% +1.4% wheel-sieve1 +0.2% +0.0% +0.0% -0.8% wheel-sieve2 +0.2% +0.0% 0.14 0.17 x2n1 +0.0% -1.3% 0.02 0.03 -------------------------------------------------------------------------------- Min +0.0% -72.0% -3.2% -3.5% Max +2.5% +3.6% +6.4% +5.5% Geometric Mean +0.2% -3.0% +0.2% +0.4%