The ServerCompiler module in IGV computes an approximation of C2's schedule for unscheduled graphs, for clustering and showing control flow information in the "Control Flow" window. This approximation uses domination information to guide the scheduling of nodes into basic blocks.

In the attached example (graph "Barrier expand"), IGV computes the following dominator tree:

idom(Block 1) = null
idom(Block 2) = Block 1
idom(Block 3) = Block 2
idom(Block 4) = Block 2
idom(Block 5) = Block 2
idom(Block 6) = Block 2
idom(Block 7) = Block 6
idom(Block 8) = Block 6
idom(Block 9) = Block 8
idom(Block 10) = Block 8
idom(Block 11) = Block 8
idom(Block 12) = Block 11
idom(Block 13) = Block 11
idom(Block 14) = Block 12
idom(Block 15) = Block 14
idom(Block 16) = Block 14
idom(Block 17) = Block 8
idom(Block 18) = Block 17
idom(Block 19) = Block 17

Whereas the expected result is:

(..)
idom(Block 11) = Block 10
(..)
idom(Block 17) = Block 10
(..)