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+# Overview
+
+The Ideal Graph Visualizer is a tool developed to help examine the intermediate
+representation of C2 which is commonly referred to as the "ideal graph". It was
+developed in collaboration with the University of Linz in Austria and has been
+included as part of hotspot since that was the primary target of the tool. The
+tool itself is fairly general with only a few modules that contain C2 specific
+elements.
+
+The tool is built on top of the NetBeans 7 rich client infrastructure and so
+requires NetBeans to build. It currently requires at least Java 6 to run as it
+needs support for JavaScript for its filtering mechanism and assumes it's built
+into the platform.  It should build out of the box with NetBeans 7.0 and Java 6
+or later.
+
+# Building and Running
+
+The build system used for IGV is ant. To download all required libraries and
+build IGV, issue `ant build`. To run IGV, use the `igv.sh` command; it will put
+all log messages generated by the run to the file `.igv.log`. To see all log
+messages generated during an IGV run, use `ant run`.
+
+# Usage
+
+The JVM support is controlled by the flag `-XX:PrintIdealGraphLevel=#` where `#`
+is:
+
+* 0: no output, the default
+* 1: dumps graph after parsing, before matching, and final code (also dumps
+     graphs for failed compilations, if available)
+* 2: more detail, including after loop opts
+* 3: even more detail
+* 4: prints graph after parsing every bytecode (very slow)
+
+By default the JVM expects that it will connect to a visualizer on the local
+host on port 4444. This can be configured using the options
+`-XX:PrintIdealGraphAddress=` and `-XX:PrintIdealGraphPort=`.
+`PrintIdealGraphAddress` can actually be a hostname.
+
+It is advisable to run the JVM with background compilation disabled (-Xbatch).
+Compilations going on in the background may be cancelled when the VM terminates,
+which can lead to incomplete dumps being sent to IGV.
+
+Alternatively the output can be sent to a file using
+`-XX:PrintIdealGraphFile=filename`. Each compiler thread will get it's own file
+with unique names being generated by adding a number onto the provided file
+name.
+
+More information about the tool is available at
+https://wiki.openjdk.java.net/display/HotSpot/IdealGraphVisualizer.