Loop Dependencies - 2021.2 English

Vitis Unified Software Platform Documentation: Application Acceleration Development (UG1393)

Document ID
UG1393
ft:locale
English (United States)
Release Date
2021-12-15
Version
2021.2 English

Data dependencies in loops can impact the results of loop pipelining or unrolling. These loop dependencies can be within a single iteration of a loop or between different iterations of a loop. The straightforward method to understand loop dependencies is to examine an extreme example. In the following code example, the result of the loop is used as the loop continuation or exit condition. Each iteration of the loop must finish before the next can start.

Minim_Loop: while (a != b) { 
  if (a > b) 
    a -= b; 
  else 
    b -= a;
}

This loop cannot be pipelined. The next iteration of the loop cannot begin until the previous iteration ends.

Dealing with various types of dependencies with the Vitis compiler is an extensive topic requiring a detailed understanding of the high-level synthesis procedures underlying the compiler. For more information, refer to the Vitis High-Level Synthesis User Guide (UG1399).