public int[] getPrimaryAlts() {
		if ( recPrimaryAlts.size()==0 ) return null;
		int[] alts = new int[recPrimaryAlts.size()+1];
		for (int i = 0; i < recPrimaryAlts.size(); i++) { // recPrimaryAlts is a List not Map like recOpAlts
			LeftRecursiveRuleAltInfo altInfo = recPrimaryAlts.get(i);
			alts[i+1] = altInfo.altNum;
		}
		return alts;
	}
Return an array that maps predicted alt from primary decision
 to original alt of rule. For following rule, return [0, 2, 4]

		e : e '*' e
		  | INT
		  | e '+' e
		  | ID
		  ;
 That maps predicted alt 1 to original alt 2 and predicted 2 to alt 4.

 @since 4.5.1
tool/src/org/antlr/v4/tool/LeftRecursiveRule.java