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 WhenClauseMightAssignPatternVariableWalker();
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;
}
return(decisionDag);
}
LearnFromDecisionDag(
SyntaxNode node,
BoundDecisionDag decisionDag,
BoundExpression expression,
TypeWithState expressionType,
ref PossiblyConditionalState 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(compilation), rootTemp);
}
Debug.Assert(originalInputSlot > 0);
// If the input of the switch (or is-pattern expression) is a tuple literal, we reuse the slots of
// those expressions (when possible), pretending that we are not copying them into a temporary ValueTuple instance
// to evaluate the patterns. In this way we infer non-nullability of the original element's parts.
// We do not extend such courtesy to nested tuple literals.
var originalInputElementSlots = expression is BoundTupleExpression tuple
? tuple.Arguments.SelectAsArray(static (a, w) => w.MakeSlot(a), this)
/// <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);
}
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);
}
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;
}
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));
}
}
}