public override void VisitBody(BoundBody node)
{
using (var marker = _typeManager.CreateDefiniteAssignmentMarker(_parentBranch))
{
_branch = marker.CreateDefaultBranch();
var block = new Block(_branch, null, false, false, null);
PushBlock(block);
base.VisitBody(node);
PopBlock(block);
ResultExpressions = _branch.Expressions;
// If the last statement of the body is a return, the return
// provides the result expression and we don't have to track
// the result expressions.
if (
node.Body.Nodes.Count == 0 ||
node.Body.Nodes[node.Body.Nodes.Count - 1] is BoundReturn
)
ResultExpressions = null;
_branch.IsKilled = true;
_branch = null;
}
}
public override void VisitWhile(BoundWhile node)
{
// Rules for while:
// * When IsFalse(Test), we don't have any work;
// * When IsTrue(Test), _branch stays the default;
// * Otherwise, _branch becomes a fork;
// * Target for break/continue.
var result = ToBoolean(node.Test);
// If Test evaluates to a constant expression false, the while
// loop is never taken.
if (result == false)
return;
// The Test is executed on the default branch.
Visit(node.Test);
var block = new Block(_branch, FindLabel(node), true, true, null);
PushBlock(block);
_branch = block.Branch.Fork();
Visit(node.Body);
block.JoinBranch(_branch);
// Create an empty fork to tell the Join algorithm that the
// Body was an optional branch.
if (result != true)
block.JoinBranch(block.Branch.Fork());
PopBlock(block);
}
private void PopBlock(Block block)
{
// Verify that we're popping the right block.
Debug.Assert(block == _blocks[_blocks.Count - 1]);
_blocks.RemoveAt(_blocks.Count - 1);
// Join any pending join branches.
if (block.Joins != null)
block.Branch.Join(block.Joins);
// Restore the current branch from the block.
_branch = block.Branch;
}
public override void VisitTry(BoundTry node)
{
// Rules for try/catch:
// * Try stays the default;
// * Catch becomes a fork (it's only taken when an exception is
// thrown);
// * Finally is treated special. It's also executed on the default
// branch, but it's also executed from break/continue/throw/return's,
// because these flow through the finally. We don't do this here,
// but in JoinOnBlock.
var block = new Block(_branch, null, false, false, node.Finally);
PushBlock(block);
Visit(node.Try);
if (node.Catch != null)
{
// Create a block for the catch.
var catchBlock = new Block(block.Branch, null, false, false, null);
PushBlock(catchBlock);
_branch = catchBlock.Branch.Fork();
Visit(node.Catch);
catchBlock.JoinBranch(_branch);
// Create an empty fork to tell the Join algorithm that the
// Catch was an optional branch.
catchBlock.JoinBranch(catchBlock.Branch.Fork());
PopBlock(catchBlock);
}
Visit(node.Finally);
PopBlock(block);
}
public Marker(BoundTypeManager typeManager, BoundTypeManager.DefiniteAssignmentMarker.Branch parentBranch)
{
_typeManager = typeManager;
_parentBranch = parentBranch;
}
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);
}
public override void VisitIf(BoundIf node)
{
// Rules for if:
// * When IsTrue(Test), Else is not taken and Then stays the
// default branch;
// * When IsFalse(Test), Then is not taken and If stays the
// default branch;
// * Otherwise, Then and Else become a fork (even when Else
// is null).
bool? result = ToBoolean(node.Test);
// If Test evaluates to a constant that allows us to skip
// the Then, and we don't have an Else, we don't have any
// work for this node.
if (result == false && node.Else == null)
return;
// Test is executed on the default branch.
Visit(node.Test);
var block = new Block(_branch, null, false, false, null);
PushBlock(block);
if (!result.HasValue)
{
// Visit the Then.
_branch = block.Branch.Fork();
Visit(node.Then);
block.JoinBranch(_branch);
// Visit the Else. Note that we always fork the branch, even
// when we don't have an Else. The reason for this is that
// the join algorithm correctly marks variables that are
// only written to in the Then branch as not definitely
// assigned.
_branch = block.Branch.Fork();
if (node.Else != null)
Visit(node.Else);
block.JoinBranch(_branch);
}
else
{
Visit(result.Value ? node.Then : node.Else);
}
PopBlock(block);
}
public override void VisitForEachIn(BoundForEachIn node)
{
// Rules for for each in:
// * _branch becomes a fork and we create an empty fork;
// * Target for break/continue.
// Expression is executed on the default branch.
Visit(node.Expression);
MarkWrite(node.Target);
var block = new Block(_branch, FindLabel(node), true, true, null);
PushBlock(block);
_branch = block.Branch.Fork();
Visit(node.Body);
block.JoinBranch(_branch);
// Create an empty branch to signal that the body is optional.
block.JoinBranch(block.Branch.Fork());
PopBlock(block);
}
public override void VisitFor(BoundFor node)
{
// Rules for for:
// * _branch stays default when IsTrue(Test); otherwise _branch
// becomes a fork;
// * Target for break/continue;
// * Increment is only executed when the default branch reaches
// the end or a continue was executed.
// Initialization and test are executed on the current branch.
Visit(node.Initialization);
Visit(node.Test);
var block = new Block(_branch, FindLabel(node), true, true, null);
_branch = block.Branch.Fork();
PushBlock(block);
Visit(node.Body);
bool wasKilled = _branch.IsKilled;
// Only visit the increment when then default branch flows there
// or a continue was executed.
if (!_branch.IsKilled || block.ContinueTaken)
{
// We need to restore the branch because if the branch is
// killed, but we have a continue, the test is still done on
// the branch.
_branch.IsKilled = false;
Visit(node.Increment);
}
if (!wasKilled)
block.JoinBranch(_branch);
// Create an extra empty branch when the test wasn't unconditional.
if (node.Test != null && ToBoolean(node.Test) != true)
block.JoinBranch(block.Branch.Fork());
PopBlock(block);
}
public override void VisitDoWhile(BoundDoWhile node)
{
// Rules for do/while:
// * _branch stays default branch (we always take the do);
// * Target for break/continue;
// * Test is only executed when the default branch reaches the end
// or a continue was executed.
var block = new Block(_branch, FindLabel(node), true, true, null);
PushBlock(block);
_branch = block.Branch.Fork();
Visit(node.Body);
bool wasKilled = _branch.IsKilled;
if (!_branch.IsKilled || block.ContinueTaken)
{
// We need to restore the branch because if the branch is
// killed, but we have a continue, the test is still done on
// the branch.
_branch.IsKilled = false;
Visit(node.Test);
}
if (!wasKilled)
block.JoinBranch(_branch);
PopBlock(block);
}