Description

In the following example, Vivado HLS reports a warning message and less than expected II and pipeline results.

Pseudo code:

If (condition) 
R = M[ax] ; 
Else 
R = M[ay]; 

@W [SCHED-69] Unable to schedule 'load' operation on array 'M' due to limited resources (II = 1).
@I [SCHED-61] Pipelining result: Target II: 1, Final II: 2, Depth: 3.

Solution

To ensure Vivado HLS can optimize HDL outputs, modify the code as shown below. 

If (condition) 
   A = ax ; 
Else 
   A = ay; 
// next do the actual read
R=M[A];

This issue is fixed  from release 2012.2 on.