http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53852
--- Comment #5 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch>
2012-08-22 11:58:00 UTC ---
simplified testcase and some analysis:
SUBROUTINE build_d_tensor_gks(d5f,v,d5)
INTEGER, PARAMETER :: dp=8
REAL(KIND=dp), DIMENSION(3, 3, 3, 3, 3), &
INTENT(OUT) :: d5f
REAL(KIND=dp), DIMENSION(3), INTENT(IN) :: v
REAL(KIND=dp), INTENT(IN) :: d5
INTEGER :: k1, k2, k3, k4, k5
REAL(KIND=dp) :: w
d5f = 0.0_dp
DO k1=1,3
DO k2=1,3
DO k3=1,3
DO k4=1,3
DO k5=1,3
d5f(k5,k4,k3,k2,k1)=d5f(k5,k4,k3,k2,k1)+ &
v(k1)*v(k2)*v(k3)*v(k4)*v(k5)*d5
ENDDO
w=v(k1)*v(k2)*v(k3)*d4
d5f(k1,k2,k3,k4,k4)=d5f(k1,k2,k3,k4,k4)+w
d5f(k1,k2,k4,k3,k4)=d5f(k1,k2,k4,k3,k4)+w
d5f(k1,k4,k2,k3,k4)=d5f(k1,k4,k2,k3,k4)+w
d5f(k4,k1,k2,k3,k4)=d5f(k4,k1,k2,k3,k4)+w
d5f(k1,k2,k4,k4,k3)=d5f(k1,k2,k4,k4,k3)+w
! d5f(k1,k4,k2,k4,k3)=d5f(k1,k4,k2,k4,k3)+w
! d5f(k4,k1,k2,k4,k3)=d5f(k4,k1,k2,k4,k3)+w
! d5f(k1,k4,k4,k2,k3)=d5f(k1,k4,k4,k2,k3)+w
! d5f(k4,k1,k4,k2,k3)=d5f(k4,k1,k4,k2,k3)+w
! d5f(k4,k4,k1,k2,k3)=d5f(k4,k4,k1,k2,k3)+w
ENDDO
ENDDO
ENDDO
ENDDO
END SUBROUTINE build_d_tensor_gks
the issue is that the compile time grows exponentially in the number of
uncommented lines of the d5f=d5f+w type:
1 0m1.112s
2 0m4.448s
3 0m11.513s
4 0m21.514s
5 0m35.529s
