1. Tracing logic for monitoring a stream of processing instructions from a program being processed by a data processor, said tracing logic comprising monitoring logic operable to: detect processing of said instructions in said instruction stream; detect which of said instructions in said instruction stream are conditional direct branch instructions, which of said instructions in said instruction stream are conditional indirect branch instructions and which of said instructions in said instruction stream are unconditional indirect branch instructions; said tracing logic further comprising compression logic operable to: designate said conditional branch instructions, said conditional indirect branch and said unconditional indirect branch instructions as marker instructions; and for each marker instruction, output an indicator indicating a behaviour of said data processor when said marker instruction is processed and not output data relating to processed instructions that are not marker instructions.