Bug#569436: blas: zgesvd seems to give incorrect results

[Denis Barbier]

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.

Denis