Developer Guide

FPGA Optimization Guide for Intel® oneAPI Toolkits

ID 767853
Date 7/13/2023
Public

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NDRange Kernels

If your program naturally tends to describe multiple concurrent threads operating in a data-parallel manner, specify your kernel to operate in parallel instances over a work-item index-space (NDRange).

Avoid Work-Item ID-Dependent Backward Branching

The Intel® oneAPI DPC++/C++ Compiler collapses conditional statements into single bits that indicate when a particular functional unit becomes active. The Intel® oneAPI DPC++/C++ Compiler eliminates simple control flow paths that do not involve looping structures, resulting in a flat control structure and more efficient hardware use.

Avoid including any work-item ID-dependent backward branching (that is, branching that occurs in a loop) in your kernel because it degrades performance.

For example, the following code fragment illustrates branching that involves work-item ID such as get_global_id or get_local_id:

for (size_t i = 0; i < get_global_id(0); i++)
{
   // statements
}