Compiling this code (AMD64 under SuSE Linux Professional 9.1):

      SUBROUTINE OPTBUG(N,A,LDA,B,LDB)
C     .. Scalar Arguments ..
      INTEGER                 LDA, LDB, N
C     .. Array Arguments ..
      REAL                    A(LDA,N), B(LDB,N)
C     .. Local Scalars ..
      REAL                    A1
      INTEGER                 I, J
C     .. Executable Statements ..
      DO 40 J = 1, N
         DO 20 I = 1, J
            A1 = A(I,J)
            B(I,J) = A1
  20     CONTINUE
  40  CONTINUE
      RETURN
      END

with optimization level -O2 or above, like this:

  gfortran -v -Wall -O2 -c optbug.f

gives the following error message:

Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc/configure --prefix=/var/tmp/gfortran-20050422/irun
--enable-languages=c,f95
Thread model: posix
gcc version 4.1.0 20050422 (experimental)
 /opt/gfortran/irun/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.1.0/f951
optbug.f -ffixed-form -quiet -dumpbase optbug.f -mtune=k8 -auxbase optbug -O2
-Wall -version -o /tmp/ccGwsoUd.s
GNU F95 version 4.1.0 20050422 (experimental) (x86_64-unknown-linux-gnu)
        compiled by GNU C version 3.4.2 20041017 (Red Hat 3.4.2-6.fc3).
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
optbug.f: In function ‘optbug’:
optbug.f:1: internal compiler error: in set_value_range, at tree-vrp.c:124
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.