Extract from subroutine DCDCMP, from SPICE in the Perfect Club

This LOD is unusual in that is caused by a dependence carried by a scalar variable. Normally scalar dependences do not cause Read-After-Write hazards, as the scalar variables can typically held in registers. In this case, however, variable j is a parameter to a call to subroutine RESERVE at line 2968. In the absence of detailed inter-procedural information, this call acts as a use of j, thus preventing the elimination of the previous store to j at line 2962.

The table search loop at lines 2979 thru 2981 is actually compiled to execute entirely on the Control Unit! The compiler realises that the loop contains a loss of decoupling on each iteration and therefore does not attempt to generate decoupled code.

2959   C     FOR EACH COLUMN ELEMENT LOOK UP ROW NXTI
2960   C     
2961   130     if (locc .eq. 0) 
2961             goto 170
2962           j = nodplc(jcolno+locc)
2963   C     
2964   C     CHECK FOR FILL-IN (I,J)
2965   C     
2966           if (ipiv .le. 0) 
2966             goto 135
2967           call sizmem(jcpt, isize1)
2968           call reserv(i, j)
2969           call sizmem(jcpt, isize2)
2970           if (isize1 .eq. isize2) 
2970             goto 135
2971           call extmem(lvn, 1)
2972           nttbr = nttbr+1
2973           value(lvn+nstop+nttbr) = 0.0d0
2974   C     
2975   C     LOCATE ELEMENT (I,J)
2976   C     

2977   135     if (j .lt. i) 
2977             goto 145
2978           locij = locc
2979   140     locij = nodplc(irpt+locij)
2980           if (nodplc(irowno+locij) .eq. i) 
2980             goto 155
2981           goto 140
2982   145     locij = locr
2983   150     locij = nodplc(jcpt+locij)
2984           if (nodplc(jcolno+locij) .eq. j) 
2984             goto 155
2985           goto 150
2986   155     value(lvn+locij) = value(lvn+locij)-value(lvn+locc)*value(lvn+locr)
2988   160     locc = nodplc(jcpt+locc)
2989           goto 130