From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Stallman To: mark@codesourcery.com Cc: jbuck@synopsys.com, gcc@gcc.gnu.org Subject: Re: type based aliasing again Date: Sat, 11 Sep 1999 00:17:00 -0000 Message-id: <199909110726.DAA03278@psilocin.gnu.org> References: <199909090502.WAA24772@atrus.synopsys.com> <199909100634.CAA01839@psilocin.gnu.org> <19990910001035T.mitchell@codesourcery.com> X-SW-Source: 1999-09/msg00434.html Naturally. But, this proposal is odd in that it will *in general* make programs work better at higher optimizations, because it is likely that the optimizer will compute more information about what aliases what. I think that will happen rarely if at all. I think so because I think almost all of these cases will be totally obvious, and GCC with -O1 or -O2 will do enough alias testing to prevent the optimizations that would make them not work as intended. But there could be some cases where this happens. It will be hard for people to figure out why their programs work with -O3 but not with -O2. They will likely conclude, in fact, that the compiler has a bug. We can live with a few users blaming us for mistakes that we did not make. Those who really care will send bug reports, and someone will explain to them why the code is not valid, and then they will change it. Right now, we have many users blaming us for a decision that the GCC maintainers did knowingly make. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Stallman To: mark@codesourcery.com Cc: jbuck@synopsys.com, gcc@gcc.gnu.org Subject: Re: type based aliasing again Date: Thu, 30 Sep 1999 18:02:00 -0000 Message-ID: <199909110726.DAA03278@psilocin.gnu.org> References: <199909090502.WAA24772@atrus.synopsys.com> <199909100634.CAA01839@psilocin.gnu.org> <19990910001035T.mitchell@codesourcery.com> X-SW-Source: 1999-09n/msg00434.html Message-ID: <19990930180200.ezrCOvRro-CI2n-uEsGYIZUo9XWAYOd537RF_3cDaB4@z> Naturally. But, this proposal is odd in that it will *in general* make programs work better at higher optimizations, because it is likely that the optimizer will compute more information about what aliases what. I think that will happen rarely if at all. I think so because I think almost all of these cases will be totally obvious, and GCC with -O1 or -O2 will do enough alias testing to prevent the optimizations that would make them not work as intended. But there could be some cases where this happens. It will be hard for people to figure out why their programs work with -O3 but not with -O2. They will likely conclude, in fact, that the compiler has a bug. We can live with a few users blaming us for mistakes that we did not make. Those who really care will send bug reports, and someone will explain to them why the code is not valid, and then they will change it. Right now, we have many users blaming us for a decision that the GCC maintainers did knowingly make.