Date: Sun, 3 Jan 2016 19:11:39 +0100 From: Joerg Sonnenberger <joerg@britannica.bec.de> To: freebsd-hackers@freebsd.org Subject: Re: variables optimized out Message-ID: <20160103181139.GA16659@britannica.bec.de> In-Reply-To: <20160103145923.GA16970@becker.bs.l> References: <CAA99N-OKyxzVaJ4ayXRUGAoovNtHFXTpOXPkwhdw9k3LEMnOtw@mail.gmail.com> <20160103145923.GA16970@becker.bs.l>
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On Sun, Jan 03, 2016 at 03:59:23PM +0100, Bertram Scharpf wrote: > Hi, > > On Sunday, 03. Jan 2016, 14:38:33 +0100, robbinson defau wrote: > > Im debugging some issues in the kernel and as the kernel is compiled by > > default with -O2, a lot of variables are optimized out. So i made changes > > to make.conf (CFLAGS and COPTFLAGS).\ > > > > All builds fine, but I get the weirdest of panics that most certainly not > > happen with -O2. [...] > > I just had a look at "man make.conf" and that says: > > CFLAGS (str) Controls the compiler setting when compiling C code. > Optimization levels other than -O and -O2 are not sup‐ > ported. > > At least to me this is a surprise. I'm really disappointed > about what programming style has become common. There are two strong historical reasons from GCC behavior: - a lot of the -O3 optimisations has been known to break questionable code - a lot of the warnings significantly change behavior depending on the optmizer. While the former is not a big problem for disabling optimisation, the latter certainly is. Note that with clang there is no difference between -O and -O2. Joerg
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