The implementation of ReplacedNodes::dump(outputStream *st) does not print to the outputStream st but dumps the output to tty. It is called by SafePointNode::dump_spec(..).

The IdealGraphPrinter uses dump_spec(..) to write to the graph file. If it encounters SafePointNodes the console output is flooded with messages.

To reproduce the bug use the following command line:
java -Xcomp -XX:PrintIdealGraphLevel=4 -XX:PrintIdealGraphFile="file.xml" -version

Output then looks like this:
[...]
replaced nodes: 26->176,176->192,197->220,220->237,249->250,250->264,269->287,287->304replaced nodes: 26->176,176->192,197->220,220->237,249->250,250->264,269->287,287->304replaced nodes: 26->176,176->192,197->220,220->237,249->250,250->264,269->287,287->304replaced nodes: 26->176,176->192,197->220,220->237,249->250,250->264,269->287,287->304replaced nodes: 26->176,176->192,197->220,220->237,249->250,250->264
[...]