What program will have diamond interference graph mentioned in BRIGGS94?

Question

I'm reading Briggs94 Improvements to Graph Coloring Register Allocation.

I'm just wondering what kind of program will have the diamond interference graph? That is for four live ranges w, x, y, z: w interferes with x, x interferes with z, z interferes with y, and y interferes with w. And there're no more other interferences.

Since both w and z interfere with x and y, at the timeline there must be a hole between live range x and y. And both w and z will cross this hole, inducing that w interferes with z, contradiction.

(Here's the link to the paper: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.23.253&rep=rep1&type=pdf)

Answer 1

A loop like

loop:        // live range w     x     y     z  
  x:=y+z;    //                start  end    |
  w:=z+x;    //          start   |          end 
  y:=x+w;    //            |    end  start  
  z:=w+y;    //           end          |   start
  goto loop; //                        |     |

generates such an interference graph.