On 2010/2/27 Kumar Appaiah wrote: > (Also CCing #571572) > > Dear Denis, > > On Sat, Feb 27, 2010 at 05:44:45PM +0100, Denis Barbier wrote: >> Hi, >> >> I played with the example provided by Kumar Appaiah, and narrowed the >> problem down to zdrot; after copying zdrot.f into the same directory >> as zgesvd_ex.f: >> $ gfortran -O2 -c zgesvd_ex.f >> $ gfortran -O2 -c zdrot.f >> $ gfortran -o zgesvd_ex zgesvd_ex.o zdrot.o -llapack >> $ ./zgesvd_ex >> gives the expected result (with libblas3gf 1.2-4), but >> $ gfortran -O2 -ftree-vectorize -c zdrot.f >> $ gfortran -o zgesvd_ex zgesvd_ex.o zdrot.o -llapack >> $ ./zgesvd_ex >> gives the wrong result. >> This looks like a bug in the gcc vectorizer, and it cannot be >> reproduced with gcc 4.5 from experimental. > > This was fantastic analysis. I actually would like to know how you > zeroed in onto zdrot to find the problem.
Hi, I used brute force ;) libblas3gf 1.2-4 is installed on my system, object files from libblas3gf 1.2-3 have been unpacked into dir1, half files are moved into dir2. then I compiled gfortran zgesvd_ex.o dir1/*.o -llapack and by dichotomy found which object file is causing trouble. > I shall now try to play around with zdrot to see if I can create a > test case which reproduces the bug, so that I can file a bug report > with GCC. I am afraid that this is not easy, and anyway GCC folks will discard your bugreport since this bug has been fixed in 4.5. But I am very interested to know the exact reason, and if there is a way to prevent this bug by modifying source files. Denis -- To UNSUBSCRIBE, email to debian-bugs-rc-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
