public virtual void VisitSwitch(BoundSwitch node)
{
DefaultVisit(node);
}
public override void VisitSwitch(BoundSwitch node)
{
MarkRead(node.Temporary);
// Mark the write as other to prevent removing of the temporary.
// The whole point of the temporary is that we require it for the
// switch construct, so it cannot be removed.
GetStatistic(node.Temporary).WriteState = WriteType.DoNotRemove;
base.VisitSwitch(node);
}
public override void VisitSwitch(BoundSwitch node)
{
// Rules for switch:
// * Target for break;
// * If we don't have any cases, there is no work;
// * If we only have a default case, _branch stays the default
// and there is no special handling;
// * Otherwise, we fully process the cases. Things become a bit
// tricky in a switch because of label fall through.
// Cases really are nested ifs. Say we have the following:
//
// switch (x) {
// case 1:
// a();
// case 2:
// b();
// break;
// }
//
// This can be rewritten as
//
// if (x == 1 || x == 2) {
// if (x == 1) {
// a();
// }
// b();
// }
//
// With this rewrite, we can construct cases as follows:
// - Every case is a fork;
// - If the branch isn't killed, we create an extra fork
// (the else of the 'if (x == 1)' above);
// - Otherwise, we create a new fork for the next case.
// - Default is treated like any other case; except that when
// we don't have a default, we create an extra fork at the
// end of the switch.
//
// One extra note: we don't have an expression here. The bound
// tree has already introduced a temporary for the result of the
// expression, so we don't have any handling for that here.
// Mark a read on the temporary.
MarkRead(node.Temporary);
// No cases means no work.
if (node.Cases.Count == 0)
return;
// When we only have a default case, we can just take the default.
// However, we're still a break target so we do need to create
// a block.
if (node.Cases.Count == 1 && node.Cases[0].Expression == null)
{
var block = new Block(_branch, FindLabel(node), true, false, null);
PushBlock(block);
base.VisitSwitch(node);
PopBlock(block);
return;
}
bool hadDefault = false;
// Push the block for the switch.
var switchBlock = new Block(_branch, FindLabel(node), true, false, null);
PushBlock(switchBlock);
// Clear the branch to signal the creation of a new branch.
BoundTypeManager.DefiniteAssignmentMarker.Branch caseBranch = null;
_branch = null;
for (int i = 0; i < node.Cases.Count; i++)
{
var @case = node.Cases[i];
if (@case.Expression == null)
hadDefault = true;
// Create a new branch for a series of cases (either the
// first one or on fall through).
if (caseBranch == null)
caseBranch = switchBlock.Branch.Fork();
// Create a new branch for the contents of this case.
_branch = caseBranch.Fork();
Visit(@case);
// Do we have a fall through (and we're not the last, because
// that doesn't fall through)?
if (!_branch.IsKilled && i != node.Cases.Count - 1)
{
// If we have a fall through, join the branch
// and an empty branch to close the current case.
// This makes this case optional.
caseBranch.Join(new[] { _branch, caseBranch.Fork() });
}
else
{
// If we don't have a fall through, check whether the
// branch is killed. If it isn't killed, we must be the
// last case and it's missing the break, which we insert
// here.
if (!_branch.IsKilled)
{
Debug.Assert(i == node.Cases.Count - 1);
JoinOnBlock(null, JoinType.Break);
}
// The case branch has already been joined on the switch
// block. Close this case and signal the creation of a new
// branch.
caseBranch = null;
}
}
// If we didn't have a default case, we need to create an empty
// branch for the else.
if (!hadDefault)
switchBlock.JoinBranch(switchBlock.Branch.Fork());
// And pop the switch block.
PopBlock(switchBlock);
}
private void EmitSwitch(BoundSwitch node)
{
// Create the label that jumps to the end of the switch.
var after = IL.DefineLabel(GetLabel(node));
_scope.BreakTargets.Push(after);
// Create the bound node to get the temporary.
var temporaryNode = new BoundGetVariable(node.Temporary);
var bodies = new List<Tuple<Label, BoundBlock>>();
// Emit the jump table.
Label? defaultTarget = null;
foreach (var @case in node.Cases)
{
if (@case.Expression == null)
{
IL.MarkSequencePoint(@case.Location);
defaultTarget = IL.DefineLabel();
bodies.Add(Tuple.Create(defaultTarget.Value, @case.Body));
}
else
{
var target = IL.DefineLabel();
IL.MarkSequencePoint(@case.Location);
EmitTest(
new BoundBinary(
BoundExpressionType.Equal,
temporaryNode,
@case.Expression
),
target
);
bodies.Add(Tuple.Create(target, @case.Body));
}
}
// Emit the jump to either the default block or after the switch.
IL.Emit(OpCodes.Br, defaultTarget.GetValueOrDefault(after.Label));
// Emit the bodies.
foreach (var body in bodies)
{
IL.MarkLabel(body.Item1);
EmitStatement(body.Item2);
}
// Emit the label after the switch.
IL.MarkLabel(after);
// Pop the break target to make the previous one available.
_scope.BreakTargets.Pop();
}