A change in the CFG file format introduced by JDK-8277496 makes the log file unreadable by the C1Visualizer tool.

The change adds a new line in the CFG file "(block has no end, cannot print successors)" that the C1Visualizer tool is not able to parse:

begin_cfg
  name "BlockListBuilder virtual void java.lang.Object.<init>()"
  begin_block
    name "B0"
    from_bci 0
    to_bci -1
    predecessors
    (block has no end, cannot print successors). <====
    xhandlers
    flags "std"
  end_block
end_cfg

There's no fundamental reason to provide the "no end block" information in the log file, instead a line tagged "successors" with an empty set of successors would be sufficient and would not break the C1Visualizer:

begin_cfg
  name "BlockListBuilder virtual void java.lang.Object.<init>()"
  begin_block
    name "B0"
    from_bci 0
    to_bci -1
    predecessors
    successors <==============
    xhandlers
    flags "std"
  end_block
end_cfg


The C1Visualizer tool is not maintained anymore, so fixing it is not an option.
An alternative solution would be to use a script to "fix" log files before opening them with the C1Visualizer, but it seems to add an unnecessary step in the process.