On Sat, Jul 16, 2016 at 6:28 PM, NightStrike <nightstr...@gmail.com> wrote: > On Fri, Jul 15, 2016 at 1:07 PM, Bin Cheng <bin.ch...@arm.com> wrote: >> Hi, >> This patch removes support for -funsafe-loop-optimizations, as well as >> -Wunsafe-loop-optimizations. By its name, this option does unsafe >> optimizations by assuming all loops must terminate and doesn't wrap. >> Unfortunately, it's not as useful as expected because: >> 1) Simply assuming loop must terminate isn't enough. What we really want is >> to analyze scalar evolution and loop niter bound under such assumptions. >> This option does nothing in this aspect. >> 2) IIRC, this option generates bogus code for some common programs, that's >> why it's disabled by default even at Ofast level. >> >> After I sent patches handling possible infinite loops in both (scev/niter) >> analyzer and vectorizer, it's a natural step to remove such options in GCC. >> This patch does so by deleting code for -funsafe-loop-optimizations, as well >> as -Wunsafe-loop-optimizations. It also deletes the two now useless tests, >> while the option interface is preserved for backward compatibility purpose. > > There are a number of bugs opened against those options, including one > that I just opened rather recently: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71769 > > but some go back far, in this case 9 years: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=34114 > > If you are going to remove the options, you should address open bugs > related to those options. Hi, Thanks for pointing me to these PRs, I will have a look at them. IMHO, the old one reports weakness in loop niter analyzer, the issue exists whether I remove unsafe-loop-optimization or not. The new one is a little bit trickier, I will put some comments on PR, and again, the issue (if it is) is in niter analyzer which has nothing to do with the option really.
Thanks, bin
