If you have libsuitesparse installed, then that's easy to reproduce, otherwise this will take me some times to prepare a selfcontained example:
hg clone http://bitbucket.org/eigen/eigen cd eigen hg up ee16e48 mkdir build cd build CXX=clang++ cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo cd test make cholmod_support_1 -j 4 && ./cholmod_support_1 This triggers and assertion, and running cholmod_support_1 into valgrind will more clearly show the problem. In the meantime, we found that using a template function like this: template<class T> void ignore( const T& ) { } to discard unused variable warnings also fixed this aggressive optimization issue. However this solution seems hazardous because the other tricks did not work, that is: a = a; (void)a; a += 0; gael On Mon, Feb 24, 2014 at 6:18 PM, David Blaikie <dblai...@gmail.com> wrote: > Clang should only be doing this to internal symbols (or it should be making > the symbol internal so it can perform such an optimization). Do you have a > standalone (at least complete, ideally minimal) example of this issue? > > > On Mon, Feb 24, 2014 at 8:58 AM, Gael Guennebaud <gael.guenneb...@gmail.com> > wrote: >> >> Hi, >> >> I've observed that clang changes the ABI when a function argument is not >> used. >> >> This is a nice optimization, but the downside is that this introduces >> segfaults when an argument is conditionally used with respect to >> compilation options (e.g., -DNDEBUG) and that both the application and >> a library instantiate this function, but only one is compiled with >> -DNDEBUG. >> >> Here is an example of how could look like such a function: >> >> template<int A, typename T> >> void foo(int a, T &t) { >> assert(A!=0 || a==0); >> if(A==0) { /* code making use of both a and t */ } >> else { /* code making use of t and A only */ } >> } >> >> and you can see a real-world example with a very ugly workaround there: >> >> https://bitbucket.org/eigen/eigen/commits/1e19a9cb83f0/ >> >> Does clang proposes a cleaner and more general workaround for such an >> issue? >> >> Thanks, >> >> Gael >> _______________________________________________ >> cfe-users mailing list >> cfe-users@cs.uiuc.edu >> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-users > > _______________________________________________ cfe-users mailing list cfe-users@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/cfe-users
