Can the sort be removed?

[yoyocat]

1. Why don't we make the regSets sorted when creating it, so we don't need to sort it here?
2. line 288, for (i < regSet.regSets[set].length - 2) { . Why length - 2, should it be length - 1?

virgil/aeneas/src/mach/GlobalRegAlloc.v3

Lines 285 to 291 in 3766c5b

	var constraintSet = regSet.regSets[constraint], j = 0;
	constraintSet = Arrays.sort(constraintSet, 0, constraintSet.length, byte.<);
	var set = regSet.regClasses[vreg.regClass.tag];
	for (i < regSet.regSets[set].length - 2) {
	var reg = regSet.regSets[set][i];
	if (j < constraintSet.length && reg == constraintSet[j]) j++;
	else graph.nodes[vreg.varNum].addInterfere(-reg);

[titzer]

That's a good question, maybe @s123unny can answer it?

[yoyocat]

This line of code:

virgil/aeneas/src/mach/GlobalRegAlloc.v3

Line 21 in 3766c5b

def availableColor = regSet.regSets[regSet.regClasses[RegClass.REF.tag]].length - 2;

Why - 2?

[s123unny]

1. I didn't think of it when I was developing this component. Sort during creation sounds better to me but I don't know if there is other impacts.
2. This is because it requires 2 temporary registors here:

virgil/aeneas/src/mach/GlobalRegAlloc.v3

Lines 936 to 941 in 3766c5b

	if (vreg.parmoveState == IN_CYCLE) {
	loc = getParallelMoveReg(vreg.regClass, 1);
	} else if (vreg.spill <= 0) {
	loc = srcreg;
	} else {
	loc = getParallelMoveReg(vreg.regClass, 0);

[yoyocat]

@titzer @s123unny Thank you for the explanation.