private void CheckSwitchErrors(
SwitchStatementSyntax node,
BoundExpression boundSwitchGoverningExpression,
ref ImmutableArray <BoundSwitchSection> switchSections,
BoundDecisionDag decisionDag,
DiagnosticBag diagnostics)
{
var reachableLabels = decisionDag.ReachableLabels;
bool isSubsumed(BoundSwitchLabel switchLabel)
{
return(!reachableLabels.Contains(switchLabel.Label));
}
// If no switch sections are subsumed, just return
if (!switchSections.Any(s => s.SwitchLabels.Any(l => isSubsumed(l))))
{
return;
}
var sectionBuilder = ArrayBuilder <BoundSwitchSection> .GetInstance(switchSections.Length);
foreach (var oldSection in switchSections)
{
var labelBuilder = ArrayBuilder <BoundSwitchLabel> .GetInstance(oldSection.SwitchLabels.Length);
foreach (var label in oldSection.SwitchLabels)
{
var newLabel = label;
if (!label.HasErrors && isSubsumed(label) && label.Syntax.Kind() != SyntaxKind.DefaultSwitchLabel)
{
var syntax = label.Syntax;
switch (syntax)
{
case CasePatternSwitchLabelSyntax p:
if (!p.Pattern.HasErrors)
{
diagnostics.Add(ErrorCode.ERR_SwitchCaseSubsumed, p.Pattern.Location);
}
break;
case CaseSwitchLabelSyntax p:
if (label.Pattern is BoundConstantPattern cp && !cp.ConstantValue.IsBad && FindMatchingSwitchCaseLabel(cp.ConstantValue, p) != label.Label)
{
// We use the traditional diagnostic when possible
diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, syntax.Location, cp.ConstantValue.GetValueToDisplay());
}
else if (!label.Pattern.HasErrors)
{
diagnostics.Add(ErrorCode.ERR_SwitchCaseSubsumed, p.Value.Location);
}
break;
/// <summary>
/// Produce assignment of the input expression. This method is also responsible for assigning
/// variables for some pattern-matching temps that can be shared with user variables.
/// </summary>
protected BoundDecisionDag ShareTempsAndEvaluateInput(
BoundExpression loweredInput,
BoundDecisionDag decisionDag,
Action <BoundExpression> addCode,
out BoundExpression savedInputExpression)
{
var inputDagTemp = BoundDagTemp.ForOriginalInput(loweredInput);
if ((loweredInput.Kind == BoundKind.Local || loweredInput.Kind == BoundKind.Parameter) &&
loweredInput.GetRefKind() == RefKind.None)
{
// If we're switching on a local variable and there is no when clause (checked by the caller),
// we assume the value of the local variable does not change during the execution of the
// decision automaton and we just reuse the local variable when we need the input expression.
// It is possible for this assumption to be violated by a side-effecting Deconstruct that
// modifies the local variable which has been captured in a lambda. Since the language assumes
// that functions called by pattern-matching are idempotent and not side-effecting, we feel
// justified in taking this assumption in the compiler too.
bool tempAssigned = _tempAllocator.TrySetTemp(inputDagTemp, loweredInput);
Debug.Assert(tempAssigned);
}
foreach (BoundDecisionDagNode node in decisionDag.TopologicallySortedNodes)
{
if (node is BoundWhenDecisionDagNode w)
{
// We share a slot for a user-declared pattern-matching variable with a pattern temp if there
// is no user-written when-clause that could modify the variable before the matching
// automaton is done with it (checked by the caller).
foreach (BoundPatternBinding binding in w.Bindings)
{
if (binding.VariableAccess is BoundLocal l)
{
Debug.Assert(l.LocalSymbol.DeclarationKind == LocalDeclarationKind.PatternVariable);
_ = _tempAllocator.TrySetTemp(binding.TempContainingValue, binding.VariableAccess);
}
}
}
}
if (loweredInput.Type.IsTupleType &&
loweredInput.Syntax.Kind() == SyntaxKind.TupleExpression &&
loweredInput is BoundObjectCreationExpression expr &&
!decisionDag.TopologicallySortedNodes.Any(n => usesOriginalInput(n)))
{
// If the switch governing expression is a tuple literal whose whole value is not used anywhere,
// (though perhaps its component parts are used), then we can save the component parts
// and assign them into temps (or perhaps user variables) to avoid the creation of
// the tuple altogether.
decisionDag = RewriteTupleInput(decisionDag, expr, addCode, out savedInputExpression);
}
internal BoundExpression LowerGeneralIsPattern(BoundIsPatternExpression node)
{
_factory.Syntax = node.Syntax;
var resultBuilder = ArrayBuilder <BoundStatement> .GetInstance();
var inputExpression = _localRewriter.VisitExpression(node.Expression);
BoundDecisionDag decisionDag = ShareTempsIfPossibleAndEvaluateInput(
node.DecisionDag, inputExpression, resultBuilder, out _);
// lower the decision dag.
ImmutableArray <BoundStatement> loweredDag = LowerDecisionDagCore(decisionDag);
resultBuilder.Add(_factory.Block(loweredDag));
Debug.Assert(node.Type is { SpecialType: SpecialType.System_Boolean });
private void ComputeLabelSet(BoundDecisionDag decisionDag)
{
// Nodes with more than one predecessor are assigned a label
var hasPredecessor = PooledHashSet <BoundDecisionDagNode> .GetInstance();
foreach (BoundDecisionDagNode node in decisionDag.TopologicallySortedNodes)
{
switch (node)
{
case BoundWhenDecisionDagNode w:
GetDagNodeLabel(node);
if (w.WhenFalse != null)
{
GetDagNodeLabel(w.WhenFalse);
}
break;
case BoundLeafDecisionDagNode d:
// Leaf can branch directly to the target
_dagNodeLabels[node] = d.Label;
break;
case BoundEvaluationDecisionDagNode e:
notePredecessor(e.Next);
break;
case BoundTestDecisionDagNode p:
notePredecessor(p.WhenTrue);
notePredecessor(p.WhenFalse);
break;
default:
throw ExceptionUtilities.UnexpectedValue(node.Kind);
}
}
hasPredecessor.Free();
return;
void notePredecessor(BoundDecisionDagNode successor)
{
if (successor != null && !hasPredecessor.Add(successor))
{
GetDagNodeLabel(successor);
}
}
}
public BoundDecisionDag GetDecisionDagForLowering(CSharpCompilation compilation)
{
BoundDecisionDag decisionDag = this.ReachabilityDecisionDag;
if (decisionDag.ContainsAnySynthesizedNodes())
{
decisionDag = DecisionDagBuilder.CreateDecisionDagForSwitchStatement(
compilation,
this.Syntax,
this.Expression,
this.SwitchSections,
this.DefaultLabel?.Label ?? this.BreakLabel,
BindingDiagnosticBag.Discarded,
forLowering: true);
Debug.Assert(!decisionDag.ContainsAnySynthesizedNodes());
}
return(decisionDag);
}
internal override BoundStatement BindSwitchStatementCore(SwitchStatementSyntax node, Binder originalBinder, BindingDiagnosticBag diagnostics)
{
Debug.Assert(SwitchSyntax.Equals(node));
if (node.Sections.Count == 0)
{
diagnostics.Add(ErrorCode.WRN_EmptySwitch, node.OpenBraceToken.GetLocation());
}
// Bind switch expression and set the switch governing type.
BoundExpression boundSwitchGoverningExpression = SwitchGoverningExpression;
diagnostics.AddRange(SwitchGoverningDiagnostics, allowMismatchInDependencyAccumulation: true);
ImmutableArray <BoundSwitchSection> switchSections = BindSwitchSections(originalBinder, diagnostics, out BoundSwitchLabel defaultLabel);
ImmutableArray <LocalSymbol> locals = GetDeclaredLocalsForScope(node);
ImmutableArray <LocalFunctionSymbol> functions = GetDeclaredLocalFunctionsForScope(node);
BoundDecisionDag decisionDag = DecisionDagBuilder.CreateDecisionDagForSwitchStatement(
compilation: this.Compilation,
syntax: node,
switchGoverningExpression: boundSwitchGoverningExpression,
switchSections: switchSections,
// If there is no explicit default label, the default action is to break out of the switch
defaultLabel: defaultLabel?.Label ?? BreakLabel,
diagnostics);
// Report subsumption errors, but ignore the input's constant value for that.
CheckSwitchErrors(node, boundSwitchGoverningExpression, ref switchSections, decisionDag, diagnostics);
// When the input is constant, we use that to reshape the decision dag that is returned
// so that flow analysis will see that some of the cases may be unreachable.
decisionDag = decisionDag.SimplifyDecisionDagIfConstantInput(boundSwitchGoverningExpression);
return(new BoundSwitchStatement(
syntax: node,
expression: boundSwitchGoverningExpression,
innerLocals: locals,
innerLocalFunctions: functions,
switchSections: switchSections,
defaultLabel: defaultLabel,
breakLabel: this.BreakLabel,
reachabilityDecisionDag: decisionDag));
}
public BoundDecisionDag GetDecisionDagForLowering(CSharpCompilation compilation)
{
BoundDecisionDag decisionDag = this.ReachabilityDecisionDag;
if (decisionDag.ContainsAnySynthesizedNodes())
{
decisionDag = DecisionDagBuilder.CreateDecisionDagForIsPattern(
compilation,
this.Syntax,
this.Expression,
this.Pattern,
this.WhenTrueLabel,
this.WhenFalseLabel,
BindingDiagnosticBag.Discarded,
forLowering: true);
Debug.Assert(!decisionDag.ContainsAnySynthesizedNodes());
}
return(decisionDag);
}
protected BoundDecisionDag ShareTempsIfPossibleAndEvaluateInput(
BoundDecisionDag decisionDag,
BoundExpression loweredSwitchGoverningExpression,
ArrayBuilder <BoundStatement> result,
out BoundExpression savedInputExpression)
{
// Note that a when-clause can contain an assignment to a
// pattern variable declared in a different when-clause (e.g. in the same section, or
// in a different section via the use of a local function), so we need to analyze all
// of the when clauses to see if they are all simple enough to conclude that they do
// not mutate pattern variables.
var mightAssignWalker = new WhenClauseMightAssignWalker();
bool canShareTemps =
!decisionDag.TopologicallySortedNodes
.Any(node => node is BoundWhenDecisionDagNode w && mightAssignWalker.MightAssignSomething(w.WhenExpression));
if (canShareTemps)
{
decisionDag = ShareTempsAndEvaluateInput(loweredSwitchGoverningExpression, decisionDag, expr => result.Add(_factory.ExpressionStatement(expr)), out savedInputExpression);
}
else
{
// assign the input expression to its temp.
BoundExpression inputTemp = _tempAllocator.GetTemp(BoundDagTemp.ForOriginalInput(loweredSwitchGoverningExpression));
Debug.Assert(inputTemp != loweredSwitchGoverningExpression);
result.Add(_factory.Assignment(inputTemp, loweredSwitchGoverningExpression));
savedInputExpression = inputTemp;
}
// In a switch statement, there is a hidden sequence point after evaluating the input at the start of
// the code to handle the decision dag. This is necessary so that jumps back from a `when` clause into
// the decision dag do not appear to jump back up to the enclosing construct.
if (IsSwitchStatement)
{
result.Add(_factory.HiddenSequencePoint());
}
return(decisionDag);
}
public BoundDecisionDag GetDecisionDagForLowering(CSharpCompilation compilation, out LabelSymbol?defaultLabel)
{
defaultLabel = this.DefaultLabel;
BoundDecisionDag decisionDag = this.ReachabilityDecisionDag;
if (decisionDag.ContainsAnySynthesizedNodes())
{
decisionDag = DecisionDagBuilder.CreateDecisionDagForSwitchExpression(
compilation,
this.Syntax,
this.Expression,
this.SwitchArms,
// there's no default label if the original switch is exhaustive.
// we generate a new label here because the new dag might not be.
defaultLabel ??= new GeneratedLabelSymbol("default"),
BindingDiagnosticBag.Discarded,
forLowering: true);
Debug.Assert(!decisionDag.ContainsAnySynthesizedNodes());
}
return(decisionDag);
}
public BoundExpression LowerIsPattern(
BoundIsPatternExpression isPatternExpression, BoundPattern pattern, CSharpCompilation compilation, DiagnosticBag diagnostics)
{
BoundDecisionDag decisionDag = isPatternExpression.DecisionDag;
LabelSymbol whenTrueLabel = isPatternExpression.WhenTrueLabel;
LabelSymbol whenFalseLabel = isPatternExpression.WhenFalseLabel;
BoundExpression loweredInput = _localRewriter.VisitExpression(isPatternExpression.Expression);
// The optimization of sharing pattern-matching temps with user variables can always apply to
// an is-pattern expression because there is no when clause that could possibly intervene during
// the execution of the pattern-matching automaton and change one of those variables.
decisionDag = ShareTempsAndEvaluateInput(loweredInput, decisionDag, expr => _sideEffectBuilder.Add(expr), out _);
var node = decisionDag.RootNode;
// We follow the "good" path in the decision dag. We depend on it being nicely linear in structure.
// If we add "or" patterns that assumption breaks down.
while (node.Kind != BoundKind.LeafDecisionDagNode && node.Kind != BoundKind.WhenDecisionDagNode)
{
switch (node)
{
case BoundEvaluationDecisionDagNode evalNode:
{
LowerOneTest(evalNode.Evaluation);
node = evalNode.Next;
}
break;
case BoundTestDecisionDagNode testNode:
{
Debug.Assert(testNode.WhenFalse is BoundLeafDecisionDagNode x && x.Label == whenFalseLabel);
if (testNode.WhenTrue is BoundEvaluationDecisionDagNode e &&
TryLowerTypeTestAndCast(testNode.Test, e.Evaluation, out BoundExpression sideEffect, out BoundExpression testExpression))
{
_sideEffectBuilder.Add(sideEffect);
AddConjunct(testExpression);
node = e.Next;
}
private void LowerDecisionDagCore(BoundDecisionDag decisionDag)
{
ImmutableArray <BoundDecisionDagNode> sortedNodes = decisionDag.TopologicallySortedNodes;
var firstNode = sortedNodes[0];
switch (firstNode)
{
case BoundWhenDecisionDagNode _:
case BoundLeafDecisionDagNode _:
// If the first node is a leaf or when clause rather than the code for the
// lowered decision dag, jump there to start.
_loweredDecisionDag.Add(_factory.Goto(GetDagNodeLabel(firstNode)));
break;
}
// Code for each when clause goes in the separate code section for its switch section.
foreach (BoundDecisionDagNode node in sortedNodes)
{
if (node is BoundWhenDecisionDagNode w)
{
LowerWhenClause(w);
}
}
ImmutableArray <BoundDecisionDagNode> nodesToLower = sortedNodes.WhereAsArray(n => n.Kind != BoundKind.WhenDecisionDagNode && n.Kind != BoundKind.LeafDecisionDagNode);
var loweredNodes = PooledHashSet <BoundDecisionDagNode> .GetInstance();
for (int i = 0, length = nodesToLower.Length; i < length; i++)
{
BoundDecisionDagNode node = nodesToLower[i];
if (loweredNodes.Contains(node))
{
Debug.Assert(!_dagNodeLabels.TryGetValue(node, out _));
continue;
}
if (_dagNodeLabels.TryGetValue(node, out LabelSymbol? label))
{
_loweredDecisionDag.Add(_factory.Label(label));
}
// If we can generate an IL switch instruction, do so
if (GenerateSwitchDispatch(node, loweredNodes))
{
continue;
}
// If we can generate a type test and cast more efficiently as an `is` followed by a null check, do so
if (GenerateTypeTestAndCast(node, loweredNodes, nodesToLower, i))
{
continue;
}
// We pass the node that will follow so we can permit a test to fall through if appropriate
BoundDecisionDagNode?nextNode = ((i + 1) < length) ? nodesToLower[i + 1] : null;
if (nextNode != null && loweredNodes.Contains(nextNode))
{
nextNode = null;
}
LowerDecisionDagNode(node, nextNode);
}
loweredNodes.Free();
}
protected (ImmutableArray <BoundStatement> loweredDag, ImmutableDictionary <SyntaxNode, ImmutableArray <BoundStatement> > switchSections) LowerDecisionDag(BoundDecisionDag decisionDag)
{
Debug.Assert(this._loweredDecisionDag.IsEmpty());
ComputeLabelSet(decisionDag);
LowerDecisionDagCore(decisionDag);
ImmutableArray <BoundStatement> loweredDag = _loweredDecisionDag.ToImmutableAndFree();
var switchSections = _switchArms.ToImmutableDictionary(kv => kv.Key, kv => kv.Value.ToImmutableAndFree());
_switchArms.Clear();
return(loweredDag, switchSections);
}
/// <summary>
/// Build the decision dag, giving an error if some cases are subsumed and a warning if the switch expression is not exhaustive.
/// </summary>
/// <param name="node"></param>
/// <param name="boundInputExpression"></param>
/// <param name="switchArms"></param>
/// <param name="decisionDag"></param>
/// <param name="diagnostics"></param>
/// <returns>true if there was a non-exhaustive warning reported</returns>
private bool CheckSwitchExpressionExhaustive(
SwitchExpressionSyntax node,
BoundExpression boundInputExpression,
ImmutableArray <BoundSwitchExpressionArm> switchArms,
out BoundDecisionDag decisionDag,
out LabelSymbol defaultLabel,
DiagnosticBag diagnostics)
{
defaultLabel = new GeneratedLabelSymbol("default");
decisionDag = DecisionDagBuilder.CreateDecisionDagForSwitchExpression(this.Compilation, node, boundInputExpression, switchArms, defaultLabel, diagnostics);
var reachableLabels = decisionDag.ReachableLabels;
foreach (BoundSwitchExpressionArm arm in switchArms)
{
if (!reachableLabels.Contains(arm.Label))
{
diagnostics.Add(ErrorCode.ERR_SwitchArmSubsumed, arm.Pattern.Syntax.Location);
}
}
if (!reachableLabels.Contains(defaultLabel))
{
// switch expression is exhaustive; no default label needed.
defaultLabel = null;
return(false);
}
// We only report exhaustive warnings when the default label is reachable through some series of
// tests that do not include a test in which the value is known to be null. Handling paths with
// nulls is the job of the nullable walker.
foreach (var n in TopologicalSort.IterativeSort <BoundDecisionDagNode>(new[] { decisionDag.RootNode }, nonNullSuccessors))
{
if (n is BoundLeafDecisionDagNode leaf && leaf.Label == defaultLabel)
{
diagnostics.Add(ErrorCode.WRN_SwitchExpressionNotExhaustive, node.SwitchKeyword.GetLocation());
return(true);
}
}
return(false);
ImmutableArray <BoundDecisionDagNode> nonNullSuccessors(BoundDecisionDagNode n)
{
switch (n)
{
case BoundTestDecisionDagNode p:
switch (p.Test)
{
case BoundDagNonNullTest t: // checks that the input is not null
return(ImmutableArray.Create(p.WhenTrue));
case BoundDagExplicitNullTest t: // checks that the input is null
return(ImmutableArray.Create(p.WhenFalse));
default:
return(BoundDecisionDag.Successors(n));
}
default:
return(BoundDecisionDag.Successors(n));
}
}
}
private BoundExpression LowerSwitchExpression(BoundConvertedSwitchExpression node)
{
_factory.Syntax = node.Syntax;
var result = ArrayBuilder <BoundStatement> .GetInstance();
var outerVariables = ArrayBuilder <LocalSymbol> .GetInstance();
var loweredSwitchGoverningExpression = _localRewriter.VisitExpression(node.Expression);
BoundDecisionDag decisionDag = ShareTempsIfPossibleAndEvaluateInput(
node.DecisionDag, loweredSwitchGoverningExpression, result, out BoundExpression savedInputExpression);
Debug.Assert(savedInputExpression != null);
// lower the decision dag.
(ImmutableArray <BoundStatement> loweredDag, ImmutableDictionary <SyntaxNode, ImmutableArray <BoundStatement> > switchSections) =
LowerDecisionDag(decisionDag);
// then add the rest of the lowered dag that references that input
result.Add(_factory.Block(loweredDag));
// A branch to the default label when no switch case matches is included in the
// decision tree, so the code in result is unreachable at this point.
// Lower each switch expression arm
LocalSymbol resultTemp = _factory.SynthesizedLocal(node.Type, node.Syntax, kind: SynthesizedLocalKind.LoweringTemp);
LabelSymbol afterSwitchExpression = _factory.GenerateLabel("afterSwitchExpression");
foreach (BoundSwitchExpressionArm arm in node.SwitchArms)
{
_factory.Syntax = arm.Syntax;
var sectionBuilder = ArrayBuilder <BoundStatement> .GetInstance();
sectionBuilder.AddRange(switchSections[arm.Syntax]);
sectionBuilder.Add(_factory.Label(arm.Label));
sectionBuilder.Add(_factory.Assignment(_factory.Local(resultTemp), _localRewriter.VisitExpression(arm.Value)));
sectionBuilder.Add(_factory.Goto(afterSwitchExpression));
var statements = sectionBuilder.ToImmutableAndFree();
if (arm.Locals.IsEmpty)
{
result.Add(_factory.StatementList(statements));
}
else
{
// Lifetime of these locals is expanded to the entire switch body, as it is possible to
// share them as temps in the decision dag.
outerVariables.AddRange(arm.Locals);
// Note the language scope of the locals, even though they are included for the purposes of
// lifetime analysis in the enclosing scope.
result.Add(new BoundScope(arm.Syntax, arm.Locals, statements));
}
}
_factory.Syntax = node.Syntax;
if (node.DefaultLabel != null)
{
result.Add(_factory.Label(node.DefaultLabel));
var objectType = _factory.SpecialType(SpecialType.System_Object);
var thrownExpression =
(implicitConversionExists(savedInputExpression, objectType) &&
_factory.WellKnownMember(WellKnownMember.System_Runtime_CompilerServices_SwitchExpressionException__ctorObject, isOptional: true) is MethodSymbol exception1)
? _factory.New(exception1, _factory.Convert(objectType, savedInputExpression)) :
(_factory.WellKnownMember(WellKnownMember.System_Runtime_CompilerServices_SwitchExpressionException__ctor, isOptional: true) is MethodSymbol exception0)
? _factory.New(exception0) :
_factory.New(_factory.WellKnownMethod(WellKnownMember.System_InvalidOperationException__ctor));
result.Add(_factory.Throw(thrownExpression));
}
result.Add(_factory.Label(afterSwitchExpression));
outerVariables.Add(resultTemp);
outerVariables.AddRange(_tempAllocator.AllTemps());
return(_factory.SpillSequence(outerVariables.ToImmutableAndFree(), result.ToImmutableAndFree(), _factory.Local(resultTemp)));
bool implicitConversionExists(BoundExpression expression, TypeSymbol type)
{
HashSet <DiagnosticInfo>?discarded = null;
Conversion c = _localRewriter._compilation.Conversions.ClassifyConversionFromExpression(expression, type, ref discarded);
return(c.IsImplicit);
}
}
private bool CheckSwitchExpressionExhaustive(
SwitchExpressionSyntax node,
BoundExpression boundInputExpression,
ImmutableArray <BoundSwitchExpressionArm> switchArms,
out BoundDecisionDag decisionDag,
out LabelSymbol defaultLabel,
BindingDiagnosticBag diagnostics)
{
defaultLabel = new GeneratedLabelSymbol("default");
decisionDag = DecisionDagBuilder.CreateDecisionDagForSwitchExpression(this.Compilation, node, boundInputExpression, switchArms, defaultLabel, diagnostics);
var reachableLabels = decisionDag.ReachableLabels;
bool hasErrors = false;
foreach (BoundSwitchExpressionArm arm in switchArms)
{
hasErrors |= arm.HasErrors;
if (!hasErrors && !reachableLabels.Contains(arm.Label))
{
diagnostics.Add(ErrorCode.ERR_SwitchArmSubsumed, arm.Pattern.Syntax.Location);
}
}
if (!reachableLabels.Contains(defaultLabel))
{
// switch expression is exhaustive; no default label needed.
defaultLabel = null;
return(false);
}
if (hasErrors)
{
return(true);
}
// We only report exhaustive warnings when the default label is reachable through some series of
// tests that do not include a test in which the value is known to be null. Handling paths with
// nulls is the job of the nullable walker.
bool wasAcyclic = TopologicalSort.TryIterativeSort <BoundDecisionDagNode>(new[] { decisionDag.RootNode }, nonNullSuccessors, out var nodes);
// Since decisionDag.RootNode is acyclic by construction, its subset of nodes sorted here cannot be cyclic
Debug.Assert(wasAcyclic);
foreach (var n in nodes)
{
if (n is BoundLeafDecisionDagNode leaf && leaf.Label == defaultLabel)
{
var samplePattern = PatternExplainer.SamplePatternForPathToDagNode(
BoundDagTemp.ForOriginalInput(boundInputExpression), nodes, n, nullPaths: false, out bool requiresFalseWhenClause, out bool unnamedEnumValue);
ErrorCode warningCode =
requiresFalseWhenClause ? ErrorCode.WRN_SwitchExpressionNotExhaustiveWithWhen :
unnamedEnumValue ? ErrorCode.WRN_SwitchExpressionNotExhaustiveWithUnnamedEnumValue :
ErrorCode.WRN_SwitchExpressionNotExhaustive;
diagnostics.Add(
warningCode,
node.SwitchKeyword.GetLocation(),
samplePattern);
return(true);
}
}
return(false);
ImmutableArray <BoundDecisionDagNode> nonNullSuccessors(BoundDecisionDagNode n)
{
switch (n)
{
case BoundTestDecisionDagNode p:
switch (p.Test)
{
case BoundDagNonNullTest t: // checks that the input is not null
return(ImmutableArray.Create(p.WhenTrue));
case BoundDagExplicitNullTest t: // checks that the input is null
return(ImmutableArray.Create(p.WhenFalse));
default:
return(BoundDecisionDag.Successors(n));
}
default:
return(BoundDecisionDag.Successors(n));
}
}
}
private BoundExpression LowerSwitchExpression(BoundConvertedSwitchExpression node)
{
// When compiling for Debug (not Release), we produce the most detailed sequence points.
var produceDetailedSequencePoints =
GenerateInstrumentation && _localRewriter._compilation.Options.OptimizationLevel != OptimizationLevel.Release;
_factory.Syntax = node.Syntax;
var result = ArrayBuilder <BoundStatement> .GetInstance();
var outerVariables = ArrayBuilder <LocalSymbol> .GetInstance();
var loweredSwitchGoverningExpression = _localRewriter.VisitExpression(node.Expression);
BoundDecisionDag decisionDag = ShareTempsIfPossibleAndEvaluateInput(
node.DecisionDag, loweredSwitchGoverningExpression, result, out BoundExpression savedInputExpression);
Debug.Assert(savedInputExpression != null);
object restorePointForEnclosingStatement = new object();
object restorePointForSwitchBody = new object();
// lower the decision dag.
(ImmutableArray <BoundStatement> loweredDag, ImmutableDictionary <SyntaxNode, ImmutableArray <BoundStatement> > switchSections) =
LowerDecisionDag(decisionDag);
if (produceDetailedSequencePoints)
{
var syntax = (SwitchExpressionSyntax)node.Syntax;
result.Add(new BoundSavePreviousSequencePoint(syntax, restorePointForEnclosingStatement));
// While evaluating the state machine, we highlight the `switch {...}` part.
var spanStart = syntax.SwitchKeyword.Span.Start;
var spanEnd = syntax.Span.End;
var spanForSwitchBody = new TextSpan(spanStart, spanEnd - spanStart);
result.Add(new BoundStepThroughSequencePoint(node.Syntax, span: spanForSwitchBody));
result.Add(new BoundSavePreviousSequencePoint(syntax, restorePointForSwitchBody));
}
// add the rest of the lowered dag that references that input
result.Add(_factory.Block(loweredDag));
// A branch to the default label when no switch case matches is included in the
// decision tree, so the code in result is unreachable at this point.
// Lower each switch expression arm
LocalSymbol resultTemp = _factory.SynthesizedLocal(node.Type, node.Syntax, kind: SynthesizedLocalKind.LoweringTemp);
LabelSymbol afterSwitchExpression = _factory.GenerateLabel("afterSwitchExpression");
foreach (BoundSwitchExpressionArm arm in node.SwitchArms)
{
_factory.Syntax = arm.Syntax;
var sectionBuilder = ArrayBuilder <BoundStatement> .GetInstance();
sectionBuilder.AddRange(switchSections[arm.Syntax]);
sectionBuilder.Add(_factory.Label(arm.Label));
var loweredValue = _localRewriter.VisitExpression(arm.Value);
if (GenerateInstrumentation)
{
loweredValue = this._localRewriter._instrumenter.InstrumentSwitchExpressionArmExpression(arm.Value, loweredValue, _factory);
}
sectionBuilder.Add(_factory.Assignment(_factory.Local(resultTemp), loweredValue));
sectionBuilder.Add(_factory.Goto(afterSwitchExpression));
var statements = sectionBuilder.ToImmutableAndFree();
if (arm.Locals.IsEmpty)
{
result.Add(_factory.StatementList(statements));
}
else
{
// Lifetime of these locals is expanded to the entire switch body, as it is possible to
// share them as temps in the decision dag.
outerVariables.AddRange(arm.Locals);
// Note the language scope of the locals, even though they are included for the purposes of
// lifetime analysis in the enclosing scope.
result.Add(new BoundScope(arm.Syntax, arm.Locals, statements));
}
}
_factory.Syntax = node.Syntax;
if (node.DefaultLabel != null)
{
result.Add(_factory.Label(node.DefaultLabel));
if (produceDetailedSequencePoints)
{
result.Add(new BoundRestorePreviousSequencePoint(node.Syntax, restorePointForSwitchBody));
}
var objectType = _factory.SpecialType(SpecialType.System_Object);
var thrownExpression =
(implicitConversionExists(savedInputExpression, objectType) &&
_factory.WellKnownMember(WellKnownMember.System_Runtime_CompilerServices_SwitchExpressionException__ctorObject, isOptional: true) is MethodSymbol exception1)
? _factory.New(exception1, _factory.Convert(objectType, savedInputExpression)) :
(_factory.WellKnownMember(WellKnownMember.System_Runtime_CompilerServices_SwitchExpressionException__ctor, isOptional: true) is MethodSymbol exception0)
? _factory.New(exception0) :
_factory.New(_factory.WellKnownMethod(WellKnownMember.System_InvalidOperationException__ctor));
result.Add(_factory.Throw(thrownExpression));
}
if (GenerateInstrumentation)
{
result.Add(_factory.HiddenSequencePoint());
}
result.Add(_factory.Label(afterSwitchExpression));
if (produceDetailedSequencePoints)
{
result.Add(new BoundRestorePreviousSequencePoint(node.Syntax, restorePointForEnclosingStatement));
}
outerVariables.Add(resultTemp);
outerVariables.AddRange(_tempAllocator.AllTemps());
return(_factory.SpillSequence(outerVariables.ToImmutableAndFree(), result.ToImmutableAndFree(), _factory.Local(resultTemp)));
bool implicitConversionExists(BoundExpression expression, TypeSymbol type)
{
HashSet <DiagnosticInfo>?discarded = null;
Conversion c = _localRewriter._compilation.Conversions.ClassifyConversionFromExpression(expression, type, ref discarded);
return(c.IsImplicit);
}
}
private BoundStatement LowerSwitchStatement(BoundSwitchStatement node)
{
_factory.Syntax = node.Syntax;
var result = ArrayBuilder <BoundStatement> .GetInstance();
var outerVariables = ArrayBuilder <LocalSymbol> .GetInstance();
var loweredSwitchGoverningExpression = _localRewriter.VisitExpression(node.Expression);
if (!node.WasCompilerGenerated && _localRewriter.Instrument)
{
// EnC: We need to insert a hidden sequence point to handle function remapping in case
// the containing method is edited while methods invoked in the expression are being executed.
var instrumentedExpression = _localRewriter._instrumenter.InstrumentSwitchStatementExpression(node, loweredSwitchGoverningExpression, _factory);
if (loweredSwitchGoverningExpression.ConstantValue == null)
{
loweredSwitchGoverningExpression = instrumentedExpression;
}
else
{
// If the expression is a constant, we leave it alone (the decision dag lowering code needs
// to see that constant). But we add an additional leading statement with the instrumented expression.
result.Add(_factory.ExpressionStatement(instrumentedExpression));
}
}
// The set of variables attached to the outer block
outerVariables.AddRange(node.InnerLocals);
// Evaluate the input and set up sharing for dag temps with user variables
BoundDecisionDag decisionDag = ShareTempsIfPossibleAndEvaluateInput(node.DecisionDag, loweredSwitchGoverningExpression, result, out _);
// lower the decision dag.
(ImmutableArray <BoundStatement> loweredDag, ImmutableDictionary <SyntaxNode, ImmutableArray <BoundStatement> > switchSections) =
LowerDecisionDag(decisionDag);
// then add the rest of the lowered dag that references that input
result.Add(_factory.Block(loweredDag));
// A branch to the default label when no switch case matches is included in the
// decision dag, so the code in `result` is unreachable at this point.
// Lower each switch section.
foreach (BoundSwitchSection section in node.SwitchSections)
{
_factory.Syntax = section.Syntax;
var sectionBuilder = ArrayBuilder <BoundStatement> .GetInstance();
sectionBuilder.AddRange(switchSections[section.Syntax]);
foreach (BoundSwitchLabel switchLabel in section.SwitchLabels)
{
sectionBuilder.Add(_factory.Label(switchLabel.Label));
}
// Add the translated body of the switch section
sectionBuilder.AddRange(_localRewriter.VisitList(section.Statements));
// By the semantics of the switch statement, the end of each section is required to be unreachable.
// So we can just seal the block and there is no need to follow it by anything.
ImmutableArray <BoundStatement> statements = sectionBuilder.ToImmutableAndFree();
if (section.Locals.IsEmpty)
{
result.Add(_factory.StatementList(statements));
}
else
{
// Lifetime of these locals is expanded to the entire switch body, as it is possible to capture
// them in a different section by using a local function as an intermediary.
outerVariables.AddRange(section.Locals);
// Note the language scope of the locals, even though they are included for the purposes of
// lifetime analysis in the enclosing scope.
result.Add(new BoundScope(section.Syntax, section.Locals, statements));
}
}
// Dispatch temps are in scope throughout the switch statement, as they are used
// both in the dispatch section to hold temporary values from the translation of
// the decision dag, and in the branches where the temp values are assigned to the
// pattern variables of matched patterns.
outerVariables.AddRange(_tempAllocator.AllTemps());
_factory.Syntax = node.Syntax;
result.Add(_factory.Label(node.BreakLabel));
BoundStatement translatedSwitch = _factory.Block(outerVariables.ToImmutableAndFree(), node.InnerLocalFunctions, result.ToImmutableAndFree());
// Only add instrumentation (such as a sequence point) if the node is not compiler-generated.
if (!node.WasCompilerGenerated && _localRewriter.Instrument)
{
translatedSwitch = _localRewriter._instrumenter.InstrumentSwitchStatement(node, translatedSwitch);
}
return(translatedSwitch);
}
LearnFromDecisionDag(
SyntaxNode node,
BoundDecisionDag decisionDag,
BoundExpression expression,
TypeWithState expressionType,
ref LocalState initialState)
{
// We reuse the slot at the beginning of a switch (or is-pattern expression), pretending that we are
// not copying the input to evaluate the patterns. In this way we infer non-nullability of the original
// variable's parts based on matched pattern parts. Mutations in `when` clauses can show the inaccuracy
// of analysis based on this choice.
var rootTemp = BoundDagTemp.ForOriginalInput(expression);
int originalInputSlot = MakeSlot(expression);
if (originalInputSlot <= 0)
{
originalInputSlot = makeDagTempSlot(expressionType.ToTypeWithAnnotations(), rootTemp);
initialState[originalInputSlot] = expressionType.State;
}
var tempMap = PooledDictionary <BoundDagTemp, (int slot, TypeSymbol type)> .GetInstance();
Debug.Assert(originalInputSlot > 0);
tempMap.Add(rootTemp, (originalInputSlot, expressionType.Type));
var nodeStateMap = PooledDictionary <BoundDecisionDagNode, (LocalState state, bool believedReachable)> .GetInstance();
nodeStateMap.Add(decisionDag.RootNode, (state: initialState.Clone(), believedReachable: true));
var labelStateMap = PooledDictionary <LabelSymbol, (LocalState state, bool believedReachable)> .GetInstance();
foreach (var dagNode in decisionDag.TopologicallySortedNodes)
{
bool found = nodeStateMap.TryGetValue(dagNode, out var nodeStateAndBelievedReachable);
Debug.Assert(found); // the topologically sorted nodes should contain only reachable nodes
(LocalState nodeState, bool nodeBelievedReachable) = nodeStateAndBelievedReachable;
SetState(nodeState);
switch (dagNode)
{
case BoundEvaluationDecisionDagNode p:
{
var evaluation = p.Evaluation;
(int inputSlot, TypeSymbol inputType) = tempMap.TryGetValue(evaluation.Input, out var slotAndType) ? slotAndType : throw ExceptionUtilities.Unreachable;
Debug.Assert(inputSlot > 0);
var inputState = this.State[inputSlot];
switch (evaluation)
{
case BoundDagDeconstructEvaluation e:
{
// https://github.com/dotnet/roslyn/issues/34232
// We may need to recompute the Deconstruct method for a deconstruction if
// the receiver type has changed (e.g. its nested nullability).
var method = e.DeconstructMethod;
int extensionExtra = method.IsStatic ? 1 : 0;
for (int i = 0; i < method.ParameterCount - extensionExtra; i++)
{
var parameterType = method.Parameters[i + extensionExtra].TypeWithAnnotations;
var output = new BoundDagTemp(e.Syntax, parameterType.Type, e, i);
int outputSlot = makeDagTempSlot(parameterType, output);
Debug.Assert(outputSlot > 0);
addToTempMap(output, outputSlot, parameterType.Type);
}
break;
}
case BoundDagTypeEvaluation e:
{
var output = new BoundDagTemp(e.Syntax, e.Type, e);
HashSet <DiagnosticInfo> discardedDiagnostics = null;
int outputSlot;
switch (_conversions.WithNullability(false).ClassifyConversionFromType(inputType, e.Type, ref discardedDiagnostics).Kind)
{
case ConversionKind.Identity:
case ConversionKind.ImplicitReference:
case ConversionKind.NoConversion:
case ConversionKind.ExplicitReference:
outputSlot = inputSlot;
break;
case ConversionKind.ExplicitNullable when AreNullableAndUnderlyingTypes(inputType, e.Type, out _):
outputSlot = GetNullableOfTValueSlot(inputType, inputSlot, out _, forceSlotEvenIfEmpty: true);
if (outputSlot < 0)
{
goto default;
}
break;
default:
outputSlot = makeDagTempSlot(TypeWithAnnotations.Create(e.Type, NullableAnnotation.NotAnnotated), output);
break;
}
State[outputSlot] = NullableFlowState.NotNull;
var outputType = TypeWithState.Create(e.Type, inputState);
addToTempMap(output, outputSlot, outputType.Type);
break;
}
case BoundDagFieldEvaluation e:
{
Debug.Assert(inputSlot > 0);
var field = (FieldSymbol)AsMemberOfType(inputType, e.Field);
int outputSlot = GetOrCreateSlot(field, inputSlot, forceSlotEvenIfEmpty: true);
Debug.Assert(outputSlot > 0);
var type = field.Type;
var output = new BoundDagTemp(e.Syntax, type, e);
addToTempMap(output, outputSlot, type);
break;
}
case BoundDagPropertyEvaluation e:
{
Debug.Assert(inputSlot > 0);
var property = (PropertySymbol)AsMemberOfType(inputType, e.Property);
var type = property.TypeWithAnnotations;
var output = new BoundDagTemp(e.Syntax, type.Type, e);
int outputSlot = GetOrCreateSlot(property, inputSlot, forceSlotEvenIfEmpty: true);
if (outputSlot <= 0)
{
// This is needed due to https://github.com/dotnet/roslyn/issues/29619
outputSlot = makeDagTempSlot(type, output);
}
Debug.Assert(outputSlot > 0);
addToTempMap(output, outputSlot, type.Type);
break;
}
case BoundDagIndexEvaluation e:
{
var type = TypeWithAnnotations.Create(e.Property.Type, NullableAnnotation.Annotated);
var output = new BoundDagTemp(e.Syntax, type.Type, e);
int outputSlot = makeDagTempSlot(type, output);
Debug.Assert(outputSlot > 0);
addToTempMap(output, outputSlot, type.Type);
break;
}
default:
throw ExceptionUtilities.UnexpectedValue(p.Evaluation.Kind);
}
gotoNode(p.Next, this.State, nodeBelievedReachable);
break;
}
case BoundTestDecisionDagNode p:
{
var test = p.Test;
bool foundTemp = tempMap.TryGetValue(test.Input, out var slotAndType);
Debug.Assert(foundTemp);
(int inputSlot, TypeSymbol inputType) = slotAndType;
var inputState = this.State[inputSlot];
Split();
switch (test)
{
case BoundDagTypeTest t:
if (inputSlot > 0)
{
learnFromNonNullTest(inputSlot, ref this.StateWhenTrue);
}
gotoNode(p.WhenTrue, this.StateWhenTrue, nodeBelievedReachable);
gotoNode(p.WhenFalse, this.StateWhenFalse, nodeBelievedReachable);
break;
case BoundDagNonNullTest t:
if (inputSlot > 0)
{
learnFromNonNullTest(inputSlot, ref this.StateWhenTrue);
}
gotoNode(p.WhenTrue, this.StateWhenTrue, nodeBelievedReachable);
gotoNode(p.WhenFalse, this.StateWhenFalse, nodeBelievedReachable & inputState.MayBeNull());
break;
case BoundDagExplicitNullTest t:
if (inputSlot > 0)
{
LearnFromNullTest(inputSlot, inputType, ref this.StateWhenTrue);
learnFromNonNullTest(inputSlot, ref this.StateWhenFalse);
}
gotoNode(p.WhenTrue, this.StateWhenTrue, nodeBelievedReachable);
gotoNode(p.WhenFalse, this.StateWhenFalse, nodeBelievedReachable);
break;
case BoundDagValueTest t:
Debug.Assert(t.Value != ConstantValue.Null);
if (inputSlot > 0)
{
learnFromNonNullTest(inputSlot, ref this.StateWhenTrue);
}
gotoNode(p.WhenTrue, this.StateWhenTrue, nodeBelievedReachable);
gotoNode(p.WhenFalse, this.StateWhenFalse, nodeBelievedReachable);
break;
default:
throw ExceptionUtilities.UnexpectedValue(test.Kind);
}
break;
}
case BoundLeafDecisionDagNode d:
// We have one leaf decision dag node per reachable label
labelStateMap.Add(d.Label, (this.State, nodeBelievedReachable));
break;
case BoundWhenDecisionDagNode w:
// bind the pattern variables, inferring their types as well
foreach (var binding in w.Bindings)
{
var variableAccess = binding.VariableAccess;
var tempSource = binding.TempContainingValue;
var foundTemp = tempMap.TryGetValue(tempSource, out var tempSlotAndType);
Debug.Assert(foundTemp);
var(tempSlot, tempType) = tempSlotAndType;
var tempState = this.State[tempSlot];
if (variableAccess is BoundLocal {
LocalSymbol: SourceLocalSymbol {
IsVar: true
} local
})
{
var inferredType = TypeWithState.Create(tempType, tempState).ToTypeWithAnnotations();
if (_variableTypes.TryGetValue(local, out var existingType))
{
// merge inferred nullable annotation from different branches of the decision tree
_variableTypes[local] = TypeWithAnnotations.Create(existingType.Type, existingType.NullableAnnotation.Join(inferredType.NullableAnnotation));
}
else
{
_variableTypes[local] = inferredType;
}
int localSlot = GetOrCreateSlot(local, forceSlotEvenIfEmpty: true);
this.State[localSlot] = tempState;
}
protected ImmutableArray <BoundStatement> LowerDecisionDagCore(BoundDecisionDag decisionDag)
{
_loweredDecisionDag = ArrayBuilder <BoundStatement> .GetInstance();
ComputeLabelSet(decisionDag);
ImmutableArray <BoundDecisionDagNode> sortedNodes = decisionDag.TopologicallySortedNodes;
var firstNode = sortedNodes[0];
switch (firstNode)
{
case BoundWhenDecisionDagNode _:
case BoundLeafDecisionDagNode _:
// If the first node is a leaf or when clause rather than the code for the
// lowered decision dag, jump there to start.
_loweredDecisionDag.Add(_factory.Goto(GetDagNodeLabel(firstNode)));
break;
}
// Code for each when clause goes in the separate code section for its switch section.
foreach (BoundDecisionDagNode node in sortedNodes)
{
if (node is BoundWhenDecisionDagNode w)
{
LowerWhenClause(w);
}
}
ImmutableArray <BoundDecisionDagNode> nodesToLower = sortedNodes.WhereAsArray(n => n.Kind != BoundKind.WhenDecisionDagNode && n.Kind != BoundKind.LeafDecisionDagNode);
var loweredNodes = PooledHashSet <BoundDecisionDagNode> .GetInstance();
for (int i = 0, length = nodesToLower.Length; i < length; i++)
{
BoundDecisionDagNode node = nodesToLower[i];
// A node may have been lowered as part of a switch dispatch, but if it had a label, we'll need to lower it individually as well
bool alreadyLowered = loweredNodes.Contains(node);
if (alreadyLowered && !_dagNodeLabels.TryGetValue(node, out _))
{
continue;
}
if (_dagNodeLabels.TryGetValue(node, out LabelSymbol label))
{
_loweredDecisionDag.Add(_factory.Label(label));
}
// If we can generate an IL switch instruction, do so
if (!alreadyLowered && GenerateSwitchDispatch(node, loweredNodes))
{
continue;
}
// If we can generate a type test and cast more efficiently as an `is` followed by a null check, do so
if (GenerateTypeTestAndCast(node, loweredNodes, nodesToLower, i))
{
continue;
}
// We pass the node that will follow so we can permit a test to fall through if appropriate
BoundDecisionDagNode nextNode = ((i + 1) < length) ? nodesToLower[i + 1] : null;
if (nextNode != null && loweredNodes.Contains(nextNode))
{
nextNode = null;
}
LowerDecisionDagNode(node, nextNode);
}
loweredNodes.Free();
var result = _loweredDecisionDag.ToImmutableAndFree();
_loweredDecisionDag = null;
return(result);
}
