The following situations may prevent a loop from being eligible for software pipelining. These can be detected by examining the assembly output and the Software Pipeline Information in the comment block.

• Loop contains function calls: Although a software pipelined loop can contain intrinsics, it cannot contain function calls. This includes code that will result in a call to un-inlinable run-time support routines, such as floating-point division. You may attempt to inline small, user-defined functions; see Section 3.3.5.
• Loop contains control code: In some cases, the compiler cannot remove all of the control flow from if-then-else statements or "?:" statements. You may attempt to optimize such situations by using if statements only around code that updates memory and around variables whose values are calculated inside the loop and used only outside the loop.
• Conditionally incremented loop control variable is not software pipelined. If a loop contains a loop control variable that is conditionally incremented, the compiler will not be able to software pipeline the loop.

  for (i = 0; i < x; i++)
  {
      . . .
      if (b > a)
          i += 2
  }
  

• Too many instructions. Oversized loops typically cannot be scheduled due to the large number of registers needed. However, some large loops require an undue amount of time for compilation. A potential solution may be to break the loop into multiple smaller loops.
• Uninitialized iteration counter. The loop counter may not have been set to an initial value.
• Cannot identify iteration counter. The loop control is too complex. Try to simplify the loop.