Loop fusion

Loop fusion, also called loop jamming, is a compiler optimization, a loop transformation, which replaces multiple loops with a single one.

Example in C

  int i, a[100], b[100];
  for (i = 0; i < 100; i++)
    a[i] = 1;                     
  for (i = 0; i < 100; i++)
    b[i] = 2;

is equivalent to:

  int i, a[100], b[100];
  for (i = 0; i < 100; i++)
  {
    a[i] = 1; 
    b[i] = 2;
  }

Note

Some optimizations like this don't always improve the run-time performance. This is due to architectures that provide better performance if there are two loops rather than one, for example due to increased data locality within each loop. In those cases, a single loop may be transformed into two, which is called loop fission.

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