// устранение переходов через переходы (пример из презентации Opt5.pdf слайд 32)
public static (bool wasChanged, IReadOnlyList <Instruction> instructions) RemoveGotoThroughGoto(IReadOnlyList <Instruction> instructions)
{
if (instructions is null)
{
throw new ArgumentNullException(nameof(instructions), "instructions is null");
}
var wasChanged = false;
var newInstructions = new List <Instruction>();
for (var i = 0; i < instructions.Count; ++i)
{
if (instructions[i].Operation == "ifgoto" && 4 <= (instructions.Count - i))
{
var com0 = instructions[i];
var com1 = instructions[i + 1];
var com2 = instructions[i + 2];
var com3 = instructions[i + 3];
// только одна операция
if (com1.Operation == "goto" && com1.Label == "" && com2.Operation != "noop" && com0.Argument2 == com2.Label && com1.Argument1 == com3.Label)
{
var tmpName = ThreeAddressCodeTmp.GenTmpName();
newInstructions.Add(new Instruction(com0.Label, "NOT", com0.Argument1, "", tmpName));
newInstructions.Add(new Instruction("", "ifgoto", tmpName, com3.Label, ""));
var label = com2.Label.StartsWith("L", StringComparison.Ordinal) && uint.TryParse(com2.Label[1..], out _) ? "" : com2.Label;
/// <summary>
/// Протянуть if с метками
/// </summary>
/// <param name="findInstruction">Инструкция, которую мы ищем</param>
/// <param name="instructions">Набор наших инструкций</param>
/// <returns>
/// Вернёт изменённые инструкции, если меток if не более двух
/// </returns>
private static List <Instruction> PropagateIfWithLabel(Instruction findInstruction, List <Instruction> instructions)
{
var findIndexIf = instructions.IndexOf(findInstruction);
if (findIndexIf == -1 ||
instructions.Where(x => instructions[findIndexIf].Label == x.Argument1 && x.Operation == "goto" && x.ToString() != instructions[findIndexIf].ToString()).Count() > 1)
{
return(instructions);
}
var findItem = instructions.Where(x => instructions[findIndexIf].Label == x.Argument1 && x.Operation == "goto").Any() ?
instructions.Where(x => instructions[findIndexIf].Label == x.Argument1 && x.Operation == "goto").ElementAt(0) :
new Instruction("", "", "", "", "");
var findIndexGoto = instructions.IndexOf(findItem);
if (findIndexGoto == -1)
{
return(instructions);
}
wasChanged = true;
instructions[findIndexGoto] = new Instruction("", instructions[findIndexIf].Operation, instructions[findIndexIf].Argument1, instructions[findIndexIf].Argument2, instructions[findIndexIf].Result);
instructions.RemoveAt(findIndexIf);
if (instructions[findIndexIf].Label == "")
{
instructions[findIndexIf].Label = ThreeAddressCodeTmp.GenTmpLabel();
}
instructions.Insert(findIndexGoto + 1, new Instruction("", "goto", instructions[findIndexIf].Label, "", ""));
return(instructions);
}