public static IReadOnlyList <Int32> GrabLabels(SwitchStmt stmt)
{
CaseLabelsGrabber grabber = new CaseLabelsGrabber();
stmt.Stmt.Accept(grabber);
return(grabber.Labels);
}
public override void CGenStmt(Env env, CGenState state)
{
// Inside a switch statement, the initializations are ignored,
// but the stack size should be changed.
List <Tuple <Env, Decln> > declns;
List <Tuple <Env, Stmt> > stmts;
var compoundStmt = this.Stmt as CompoundStmt;
if (compoundStmt == null)
{
throw new NotImplementedException();
}
declns = compoundStmt.Declns;
stmts = compoundStmt.Stmts;
// Track all case values.
IReadOnlyList <Int32> values = CaseLabelsGrabber.GrabLabels(this);
// Make sure there are no duplicates.
if (values.Distinct().Count() != values.Count)
{
throw new InvalidOperationException("case labels not unique.");
}
// Request labels for these values.
Dictionary <Int32, Int32> value_to_label = values.ToDictionary(value => value, value => state.RequestLabel());
Int32 label_finish = state.RequestLabel();
Int32 num_default_stmts = stmts.Count(_ => _.Item2 is DefaultStmt);
if (num_default_stmts > 1)
{
throw new InvalidOperationException("duplicate defaults.");
}
Int32 label_default =
num_default_stmts == 1 ?
state.RequestLabel() :
label_finish;
Int32 saved_stack_size = state.StackSize;
Int32 stack_size =
declns.Any() ?
declns.Last().Item1.StackSize :
saved_stack_size;
// 1. Evaluate Expr.
CGenExprStmt(env, this.Expr, state);
// 2. Expand stack.
state.CGenForceStackSizeTo(stack_size);
// 3. Make the Jump list.
foreach (KeyValuePair <Int32, Int32> value_label_pair in value_to_label)
{
state.CMPL(value_label_pair.Key, Reg.EAX);
state.JZ(value_label_pair.Value);
}
state.JMP(label_default);
// 4. List all the statements.
state.InSwitch(label_finish, label_default, value_to_label);
foreach (Tuple <Env, Stmt> env_stmt_pair in stmts)
{
env_stmt_pair.Item2.CGenStmt(env_stmt_pair.Item1, state);
}
state.OutLabels();
// 5. finish:
state.CGenLabel(label_finish);
// 6. Restore stack size.
state.CGenForceStackSizeTo(saved_stack_size);
}
public static IReadOnlyList<Int32> GrabLabels(SwitchStmt stmt) {
CaseLabelsGrabber grabber = new CaseLabelsGrabber();
stmt.Stmt.Accept(grabber);
return grabber.Labels;
}