Add IRDumper for Scala IR

[Akirathan]

Pull Request Description

Debugging/inspecting/watching changes in the Scala IR has always been very tricky. The only way to do that, other than attaching the debugger and inspecting nested object structures, has been IR.pretty method, that is not useful for large IRs. This PR add an IRDumper utility class that dumps the IR into a GraphViz textual format that can be further processed by the dot program to generate, e.g., svg files from these IRs.

A simple example (dumped by IRDumper into a file that is processed with dot -O -Tsvg file):

Important Notes

• GraphViz format is even simpler than JSON format.
• No dependencies added, just 3 simple Java classes.
• Dumping the IR is optional and not used anywhere, when desired, one can dump IRs for example from Compiler.runPipeline

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.

[4e6]

I'd move the code to a separate SBT project. Otherwise, it looks good to me

[hubertp]

I'd move the code to a separate SBT project. Otherwise, it looks good to me

Yes, maybe it should reside in tools?

[Akirathan]

I'd move the code to a separate SBT project. Otherwise, it looks good to me

@4e6 @hubertp I don't think this is a viable option for now. This tool (a single class) is meant to be used inside the runtime-compiler project, for example from Compiler.runCompilerPipeline or inside PassManager to dump graphs after every IR pass. It is not really a standalone tool.

[JaroslavTulach]

I believe that having this output in the IGV format would allow us to compare individual pipeline steps more easily.