compiling with current trunk:

MODULE hfx_contract_block
  INTEGER, PARAMETER :: dp=KIND(0.0D0)
CONTAINS
  SUBROUTINE block_4_1_1_1(kbd,kbc,kad,kac,pbd,pbc,pad,pac,prim,scale)
    REAL(KIND=dp) :: kbd(1*1), kbc(1*1), kad(4*1), kac(4*1), pbd(1*1), &
      pbc(1*1), pad(4*1), pac(4*1), prim(4*1*1*1), scale
    INTEGER                                  :: ma, mb, mc, md, p_index
    REAL(KIND=dp)                            :: ks_bc, ks_bd, p_bc, p_bd, tmp
      DO md = 1,1
        DO mc = 1,1
          DO mb = 1,1
            DO ma = 1,4
              p_index=p_index+1
              tmp = scale*prim(p_index)
              kad((md-1)*4+ma) =  kad((md-1)*4+ma)-tmp*p_bc
              kac((mc-1)*4+ma) = kac((mc-1)*4+ma)-tmp*p_bd
            END DO
          END DO
        END DO
      END DO
  END SUBROUTINE block_4_1_1_1
END MODULE hfx_contract_block

leads to

gfortran -c -g -O2 -ffast-math -funroll-loops -ftree-vectorize -march=native
-ffree-form bug.f90
bug.f90: In function ‘block_4_1_1_1’:
bug.f90:4:0: error: definition in block 8 does not dominate use in block 14
for SSA_NAME: p_index_17 in statement:
# DEBUG p_index => p_index_17
bug.f90:4:0: internal compiler error: verify_ssa failed
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

more details:
arget: x86_64-unknown-linux-gnu
Configured with: /data03/vondele/gcc_trunk/gcc/configure --disable-bootstrap
--prefix=/data03/vondele/gcc_trunk/build --enable-languages=c,c++,fortran
--disable-multilib --with-ppl=/data03/vondele/gcc_trunk/build/
--with-cloog=/data03/vondele/gcc_trunk/build/
--with-libelf=/data03/vondele/libelf-0.8.12/build/ --enable-gold --enable-lto
--enable-plugins
Thread model: posix
gcc version 4.5.0 20091103 (experimental) [trunk revision 153852] (GCC) 
COLLECT_GCC_OPTIONS='-c' '-g' '-O2' '-ffast-math' '-funroll-loops'
'-ffree-form' '-v' '-mtune=generic'

/data03/vondele/gcc_trunk/build/libexec/gcc/x86_64-unknown-linux-gnu/4.5.0/f951
bug.f90 -quiet -dumpbase bug.f90 -mtune=generic -auxbase bug -g -O2 -version
-ffast-math -funroll-loops -ffree-form -fintrinsic-modules-path
/data03/vondele/gcc_trunk/build/lib/gcc/x86_64-unknown-linux-gnu/4.5.0/finclude
-o /tmp/ccVISL4z.s


-- 
           Summary: internal compiler error: verify_ssa failed
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jv244 at cam dot ac dot uk


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41926