Burst Inference Failure 9 - 2020.1 English

Vitis HLS Messaging (UG1448)

Document ID
UG1448
Release Date
2020-06-03
Version
2020.1 English

Explanation

Burst inferencing will fail if it detects overlapping accesses of array elements. Consider rewriting the code to eliminate any overlapping accesses in the same region.

Examples

  • Loop-carried dependency with RAW dependence:
    //////////// ORIGINAL ////////////
    void foo(int *a) {
      for (long i = 2; i < 256; ++i)
        a[i] = a[i-2];
    }
     
    //////////// UPDATED ////////////
    // Remove overlapping accesses in the same region
    void foo(int *a, int *b, int n) {
      int t0 = a[0];
      int t1 = a[1];
      for (int i = 2; i < n; ++i) {
        int t2 = t0;
        a[i] = t2;
        t2 = t1;
        t1 = t0;
        t0 = t2;
      }
    }
  • Anti-dependency (WAR):
    //////////// ORIGINAL ////////////
    void foo(int *a, int n) {
      int buff[50];
      for (long i = 0; i < n; ++i) {
        buff[i] = a[i] + 100;
        ...
        a[i] = buff[i];
      }
    }
     
    //////////// UPDATED ////////////
    // Remove overlapping accesses in the same region
    void foo(int *a, int n) {
      int buff[50];
      for (long i = 0; i < n; ++i) {
        buff[i] = a[i] + 100;
        ...
      }
      for (long i = 0; i < n; ++i)
        a[i] = buff[i];
    }