2.4.1 Last Depth to Optimize Control -l <depth>

-l <depth>: this option sets the last loop depth to be optimized in control. The higher this depth, the less control overhead. For instance, with some input file, a user can generate different pseudo-codes with different depth values as shown below.

/* Generated using a given input file and option -l 1 */
for (i=0;i<=M;i++) {
  S1 ;
  for (j=0;j<=N;j++) {
    S2 ;
  }
  for (j=0;j<=N;j++) {
    S3 ;
  }
  S4 ;
}

/* Generated using the same input file but option -l 2 */
for (i=0;i<=M;i++) {
  S1 ;
  for (j=0;j<=N;j++) {
    S2 ;
    S3 ;
  }
  S4 ;
}

In this example we can see that this option can change the operation execution order between statements. Let us remind that CLooG does not make any speculation on dependences between statements (see section Defining a Scanning Order: Scattering Functions). Thus if nothing (i.e. scattering functions) forbids this, CLooG considers the above codes to be equivalent. If there is no scattering functions, the minimum value for depth is 1 (in the case of 0, the user doesn’t really need a loop generator !), and the number of scattering dimensions otherwise (CLooG will warn the user if he doesn’t respect such constraint). The maximum value for depth is -1 (infinity). Default value is infinity.

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