Phi "from" labels reference removed nodes

[DSouzaM]

On Phi nodes, each incoming data edge is associated with a particular input to the Phi's associated Merge node. Seafoam renders a "from ID" label to denote which branch a value comes from, but sometimes node ID is hidden in the rendered graph.

For example:

This graph references nodes 14 and 16, which have been removed from the graph. In this case, these nodes are just End nodes (maybe this is always the case? I'm not familiar with Graal graph invariants):

Since these nodes are removed from the graph entirely, we can't simply update the label to reference the End's predecessor. Could we assume the Merge inputs are in the same order as the Phi inputs?

(In any case, not a big blocker for me. I'm content to manually rewrite the .dot files for the small graphs I'm working with.)

[chrisseaton]

Right - thanks we'll fix that.

[chrisseaton]

Sub-task - add an assertion that labels only reference visible nodes.