8371419: IGV: Add view to visualise dominator tree and dominator information

[dafedafe]

This change introduces a dominator tree view in IGV’s CFG panel, enabling users to toggle between the control flow graph and the dominator tree. This makes dominator relationships easier to inspect than the current stdout-based output (-XX:+PrintDominators).

Motivation

• Today, dominator information is difficult to access (e.g. via -XX:+PrintDominators, which is hard to read and correlate with the graph).
• IGV already computes dominators for some phases but does not visualize them.
• Comparing dominator trees across graphs/phases was not supported.

What’s New

1. Toggle in the CFG view (toolbar button () to switch between:
   • Control Flow Graph (CFG)
   • Dominator Tree
2. Dominator edge coloring to indicate provenance:
   • Blue: dominator info provided by C2 (from GCM phase onward for now, a follow RFE will handle loop optimization dominator information)
   • Red: dominator info computed by IGV (pre-GCM)
3. Graph comparison enhancements:
   • Compare dominator trees between graphs (new)
   • Compare CFG differences between graphs (previously missing)
4. Node annotations:
   • idom: immediate dominator
   • dom_depth: dominator depth
   • block: numeric block ID for all nodes in a block

The resulting main view looks like this:

Testing

• Tier 1-3
• Manual testing in IGV

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8371419: IGV: Add view to visualise dominator tree and dominator information (Enhancement - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/28293/head:pull/28293
$ git checkout pull/28293

Update a local copy of the PR:
$ git checkout pull/28293
$ git pull https://git.openjdk.org/jdk.git pull/28293/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 28293

View PR using the GUI difftool:
$ git pr show -t 28293

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/28293.diff

Using Webrev

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Webrevs

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