protected void gatherSemantics() {
		AssemblyProduction rec =
			grammar.getPureRecursion(grammar.getNonTerminal(grammar.getStartName()));
		if (rec == null) {
			return;
		}
		for (AssemblyConstructorSemantic sem : grammar.getSemantics(rec)) {
			semantics.get(grammar.getStartName()).add(sem);
		}
	}
Gather all the semantics that can be used as state transitions

<p>
Currently, only semantics from {@code :^instruction} constructors are taken.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/assembler/sleigh/sem/AssemblyContextGraph.java