// SwitchCase
private void DefaultWalk(SwitchCase node)
{
if (Walk(node)) {
WalkNode(node.Body);
}
PostWalk(node);
}
// SwitchStatement
protected internal override bool Walk(SwitchStatement node)
{
// The expression is evaluated always.
// Then each case clause expression is evaluated until match is found.
// Therefore, the effects of the case clause expressions accumulate.
// Default clause is evaluated last (so all case clause expressions must
// accumulate first)
WalkNode(node.TestValue);
// Flow all the cases, they all start with the same initial state
int count;
IList <SwitchCase> cases = node.Cases;
if (cases != null && (count = cases.Count) > 0)
{
SwitchCase @default = null;
// Save the initial state
BitArray entry = _bits;
// The state to progressively accumualte effects of the case clause expressions
BitArray values = new BitArray(entry);
// State to flow the case clause bodies.
BitArray caseFlow = new BitArray(_bits.Length);
// The state to accumulate results into
BitArray result = new BitArray(_bits.Length, true);
PushStatement(result);
for (int i = 0; i < count; i++)
{
if (cases[i].IsDefault)
{
Debug.Assert(@default == null);
// postpone the default case
@default = cases[i];
continue;
}
// Set the state for the walking of the body
caseFlow.SetAll(false);
caseFlow.Or(values);
// Walk the body
_bits = caseFlow;
WalkNode(cases[i].Body);
// Accumulate the result into the overall case statement result.
result.And(caseFlow);
}
// Walk the default at the end.
if (@default != null)
{
// Initialize
caseFlow.SetAll(false);
caseFlow.Or(values);
// Walk the default body
_bits = caseFlow;
WalkNode(@default.Body);
// Accumulate.
result.And(caseFlow);
// If there's a default clause, exactly one case got executed.
// The final state is 'and' across all cases, stored in 'result'
entry.SetAll(false);
entry.Or(result);
}
else
{
// In the absence of default clause, we may have executed case,
// but didn't have to, so the result is an 'and' between the cases
// and the initial state.
entry.And(result);
}
PopStatement();
// Restore the original state.
_bits = entry;
}
return(false);
}
private static bool UniqueCaseValues(SwitchCase[] cases, int min, int max)
{
int length = cases.Length;
// If we have small number of cases, use straightforward N2 algorithm
// which doesn't allocate memory
if (length < N2Threshold) {
for (int i = 0; i < length; i++) {
SwitchCase sci = cases[i];
if (sci.IsDefault) {
continue;
}
for (int j = i + 1; j < length; j++) {
SwitchCase scj = cases[j];
if (scj.IsDefault) {
continue;
}
if (sci.Value == scj.Value) {
// Duplicate value found
return false;
}
}
}
return true;
}
// We have at least N2Threshold items so the min and max values
// are set to actual values and not the Int32.MaxValue and Int32.MaxValue
Debug.Assert(min <= max);
long delta = (long)max - (long)min;
if (delta < BitArrayThreshold) {
BitArray ba = new BitArray((int)delta + 1, false);
for (int i = 0; i < length; i++) {
SwitchCase sc = cases[i];
if (sc.IsDefault) {
continue;
}
// normalize to 0 .. (max - min)
int val = sc.Value - min;
if (ba.Get(val)) {
// Duplicate value found
return false;
}
ba.Set(val, true);
}
return true;
}
// Too many values that are too spread around. Use dictionary
// Using Dictionary<int, object> as it is used elsewhere to
// minimize the impact of generic instantiation
Dictionary<int, object> dict = new Dictionary<int, object>(length);
for (int i = 0; i < length; i++) {
SwitchCase sc = cases[i];
if (sc.IsDefault) {
continue;
}
int val = sc.Value;
if (dict.ContainsKey(val)) {
// Duplicate value found
return false;
}
dict[val] = null;
}
return true;
}
internal Expression Reduce()
{
// Visit body
Expression body = Visit(_generator.Body);
Debug.Assert(_returnLabels.Count == 1);
// Add the switch statement to the body
int count = _yields.Count;
var cases = new SwitchCase[count + 1];
for (int i = 0; i < count; i++)
{
cases[i] = Expression.SwitchCase(Expression.Goto(_yields[i].Label), AstUtils.Constant(_yields[i].State));
}
cases[count] = Expression.SwitchCase(Expression.Goto(_returnLabels.Peek()), AstUtils.Constant(Finished));
Type generatorNextOfT = typeof(GeneratorNext <>).MakeGenericType(_generator.Target.Type);
// Create the lambda for the GeneratorNext<T>, hoisting variables
// into a scope outside the lambda
var allVars = new List <ParameterExpression>(_vars);
allVars.AddRange(_temps);
// Collect temps that don't have to be closed over
var innerTemps = new ReadOnlyCollectionBuilder <ParameterExpression>(1 + (_labelTemps?.Count ?? 0));
innerTemps.Add(_gotoRouter);
if (_labelTemps != null)
{
foreach (LabelInfo info in _labelTemps.Values)
{
innerTemps.Add(info.Temp);
}
}
body = Expression.Block(
allVars,
Expression.Lambda(
generatorNextOfT,
Expression.Block(
innerTemps,
Expression.Switch(Expression.Assign(_gotoRouter, _state), cases),
body,
Expression.Assign(_state, AstUtils.Constant(Finished)),
Expression.Label(_returnLabels.Peek())
),
_generator.Name,
new ParameterExpression[] { _state, _current }
)
);
// Enumerable factory takes Func<GeneratorNext<T>> instead of GeneratorNext<T>
if (_generator.IsEnumerable)
{
body = Expression.Lambda(body);
}
// We can't create a ConstantExpression of _debugCookies array here because we walk the tree
// after constants have already been rewritten. Instead we create a NewArrayExpression node
// which initializes the array with contents from _debugCookies
Expression debugCookiesArray = null;
if (_debugCookies != null)
{
Expression[] debugCookies = new Expression[_debugCookies.Count];
for (int i = 0; i < _debugCookies.Count; i++)
{
debugCookies[i] = AstUtils.Constant(_debugCookies[i]);
}
debugCookiesArray = Expression.NewArrayInit(
typeof(int),
debugCookies);
}
// Generate a call to ScriptingRuntimeHelpers.MakeGenerator<T>(args)
return(Expression.Call(
typeof(ScriptingRuntimeHelpers),
"MakeGenerator",
new[] { _generator.Target.Type },
(debugCookiesArray != null)
? new[] { body, debugCookiesArray }
: new[] { body }
));
}