I am really confused by these red fork symbols. What do them mean?
arjunh
They just mean that the results of those lanes for those specific instructions should be discarded, since they aren't actually executed for the given input (if you were to execute the instructions sequentially across the inputs in the vector lane, rather than in parallel in lockstep).
Take a look at the next slide, which talks more about convergence/divergence.
I am really confused by these red fork symbols. What do them mean?
They just mean that the results of those lanes for those specific instructions should be discarded, since they aren't actually executed for the given input (if you were to execute the instructions sequentially across the inputs in the vector lane, rather than in parallel in lockstep).
Take a look at the next slide, which talks more about convergence/divergence.