C# LabelSymbol类代码示例

        internal static void AssertIsLabeledStatementWithLabel(this BoundStatement node, LabelSymbol label)
        {
            Debug.Assert(node != null);

            switch (node.Kind)
            {
                case BoundKind.LabelStatement:
                    Debug.Assert(((BoundLabelStatement)node).Label == label);
                    break;

                case BoundKind.LabeledStatement:
                    Debug.Assert(((BoundLabeledStatement)node).Label == label);
                    break;

                case BoundKind.SwitchSection:
                    foreach (var boundSwitchLabel in ((BoundSwitchSection)node).BoundSwitchLabels)
                    {
                        if (boundSwitchLabel.Label == label)
                        {
                            return;
                        }
                    }
                    throw ExceptionUtilities.Unreachable;

                default:
                    throw ExceptionUtilities.UnexpectedValue(node.Kind);
            }
        }

        internal static void AssertIsLabeledStatementWithLabel(this BoundStatement node, LabelSymbol label)
        {
            Debug.Assert(node != null);

            switch (node.Kind)
            {
                case BoundKind.LabelStatement:
                    Debug.Assert(((BoundLabelStatement)node).Label == label);
                    break;

                case BoundKind.LabeledStatement:
                    Debug.Assert(((BoundLabeledStatement)node).Label == label);
                    break;

                case BoundKind.SwitchSection:
                    foreach (var boundSwitchLabel in ((BoundSwitchSection)node).BoundSwitchLabels)
                    {
                        if (boundSwitchLabel.Label == label)
                        {
                            return;
                        }
                    }
                    Debug.Assert(false);
                    break;

                default:
                    Debug.Assert(false);
                    break;
            }
        }

        protected override void ResolveBranch(PendingBranch pending, LabelSymbol label, BoundStatement target, ref bool labelStateChanged)
        {
            // branches into a region are considered entry points
            if (IsInside && pending.Branch != null && !RegionContains(pending.Branch.Syntax.Span))
            {
                pending.State = pending.State.Reachable ? ReachableState() : UnreachableState();
            }

            base.ResolveBranch(pending, label, target, ref labelStateChanged);
        }

        private BoundStatement MakeSwitchStatement(
            CSharpSyntaxNode syntax,
            BoundExpression rewrittenExpression,
            ImmutableArray<BoundSwitchSection> rewrittenSections,
            LabelSymbol constantTargetOpt,
            ImmutableArray<LocalSymbol> locals,
            GeneratedLabelSymbol breakLabel,
            BoundSwitchStatement oldNode)
        {
            Debug.Assert(oldNode != null);
            Debug.Assert((object)rewrittenExpression.Type != null);

            return rewrittenExpression.Type.IsNullableType() ?
                MakeSwitchStatementWithNullableExpression(syntax, rewrittenExpression, rewrittenSections, constantTargetOpt, locals, breakLabel, oldNode) :
                MakeSwitchStatementWithNonNullableExpression(syntax, null, rewrittenExpression, rewrittenSections, constantTargetOpt, locals, breakLabel, oldNode);
        }

        private void EmitStringSwitchJumpTable(
            BoundSwitchStatement switchStatement,
            KeyValuePair<ConstantValue, object>[] switchCaseLabels,
            LabelSymbol fallThroughLabel,
            LocalOrParameter key,
            SyntaxNode syntaxNode)
        {
            LocalDefinition keyHash = null;

            // Condition is necessary, but not sufficient (e.g. might be missing a special or well-known member).
            if (SwitchStringJumpTableEmitter.ShouldGenerateHashTableSwitch(_module, switchCaseLabels.Length))
            {
                Debug.Assert(_module.SupportsPrivateImplClass);

                var privateImplClass = _module.GetPrivateImplClass(syntaxNode, _diagnostics);
                Cci.IReference stringHashMethodRef = privateImplClass.GetMethod(PrivateImplementationDetails.SynthesizedStringHashFunctionName);

                // Heuristics and well-known member availability determine the existence
                // of this helper.  Rather than reproduce that (language-specific) logic here,
                // we simply check for the information we really want - whether the helper is
                // available.
                if (stringHashMethodRef != null)
                {
                    // static uint ComputeStringHash(string s)
                    // pop 1 (s)
                    // push 1 (uint return value)
                    // stackAdjustment = (pushCount - popCount) = 0

                    _builder.EmitLoad(key);
                    _builder.EmitOpCode(ILOpCode.Call, stackAdjustment: 0);
                    _builder.EmitToken(stringHashMethodRef, syntaxNode, _diagnostics);

                    var UInt32Type = _module.Compilation.GetSpecialType(SpecialType.System_UInt32);
                    keyHash = AllocateTemp(UInt32Type, syntaxNode);

                    _builder.EmitLocalStore(keyHash);
                }
            }

            Cci.IReference stringEqualityMethodRef = _module.Translate(switchStatement.StringEquality, syntaxNode, _diagnostics);

            Cci.IMethodReference stringLengthRef = null;
            var stringLengthMethod = _module.Compilation.GetSpecialTypeMember(SpecialMember.System_String__Length) as MethodSymbol;
            if (stringLengthMethod != null && !stringLengthMethod.HasUseSiteError)
            {
                stringLengthRef = _module.Translate(stringLengthMethod, syntaxNode, _diagnostics);
            }

            SwitchStringJumpTableEmitter.EmitStringCompareAndBranch emitStringCondBranchDelegate =
                (keyArg, stringConstant, targetLabel) =>
                {
                    if (stringConstant == ConstantValue.Null)
                    {
                        // if (key == null)
                        //      goto targetLabel
                        _builder.EmitLoad(keyArg);
                        _builder.EmitBranch(ILOpCode.Brfalse, targetLabel, ILOpCode.Brtrue);
                    }
                    else if (stringConstant.StringValue.Length == 0 && stringLengthRef != null)
                    {
                        // if (key != null && key.Length == 0)
                        //      goto targetLabel

                        object skipToNext = new object();
                        _builder.EmitLoad(keyArg);
                        _builder.EmitBranch(ILOpCode.Brfalse, skipToNext, ILOpCode.Brtrue);

                        _builder.EmitLoad(keyArg);
                        // Stack: key --> length
                        _builder.EmitOpCode(ILOpCode.Call, 0);
                        var diag = DiagnosticBag.GetInstance();
                        _builder.EmitToken(stringLengthRef, null, diag);
                        Debug.Assert(diag.IsEmptyWithoutResolution);
                        diag.Free();

                        _builder.EmitBranch(ILOpCode.Brfalse, targetLabel, ILOpCode.Brtrue);
                        _builder.MarkLabel(skipToNext);
                    }
                    else
                    {
                        this.EmitStringCompareAndBranch(key, syntaxNode, stringConstant, targetLabel, stringEqualityMethodRef);
                    }
                };

            _builder.EmitStringSwitchJumpTable(
                caseLabels: switchCaseLabels,
                fallThroughLabel: fallThroughLabel,
                key: key,
                keyHash: keyHash,
                emitStringCondBranchDelegate: emitStringCondBranchDelegate,
                computeStringHashcodeDelegate: SynthesizedStringSwitchHashMethod.ComputeStringHash);

            if (keyHash != null)
            {
                FreeTemp(keyHash);
            }
        }

        private void EmitSwitchHeader(
            BoundSwitchStatement switchStatement,
            BoundExpression expression,
            KeyValuePair<ConstantValue, object>[] switchCaseLabels,
            LabelSymbol fallThroughLabel)
        {
            Debug.Assert(expression.ConstantValue == null);
            Debug.Assert((object)expression.Type != null &&
                expression.Type.IsValidV6SwitchGoverningType());
            Debug.Assert(switchCaseLabels.Length > 0);

            Debug.Assert(switchCaseLabels != null);

            LocalDefinition temp = null;
            LocalOrParameter key;
            BoundSequence sequence = null;

            if (expression.Kind == BoundKind.Sequence)
            {
                sequence = (BoundSequence)expression;
                DefineLocals(sequence);
                EmitSideEffects(sequence);
                expression = sequence.Value;
            }

            if (expression.Kind == BoundKind.SequencePointExpression)
            {
                var sequencePointExpression = (BoundSequencePointExpression)expression;
                EmitSequencePoint(sequencePointExpression);
                expression = sequencePointExpression.Expression;
            }

            switch (expression.Kind)
            {
                case BoundKind.Local:
                    var local = ((BoundLocal)expression).LocalSymbol;
                    if (local.RefKind == RefKind.None && !IsStackLocal(local))
                    {
                        key = this.GetLocal(local);
                        break;
                    }
                    goto default;

                case BoundKind.Parameter:
                    var parameter = (BoundParameter)expression;
                    if (parameter.ParameterSymbol.RefKind == RefKind.None)
                    {
                        key = ParameterSlot(parameter);
                        break;
                    }
                    goto default;

                default:
                    EmitExpression(expression, true);
                    temp = AllocateTemp(expression.Type, expression.Syntax);
                    _builder.EmitLocalStore(temp);
                    key = temp;
                    break;
            }

            // Emit switch jump table            
            if (expression.Type.SpecialType != SpecialType.System_String)
            {
                _builder.EmitIntegerSwitchJumpTable(switchCaseLabels, fallThroughLabel, key, expression.Type.EnumUnderlyingType().PrimitiveTypeCode);
            }
            else
            {
                this.EmitStringSwitchJumpTable(switchStatement, switchCaseLabels, fallThroughLabel, key, expression.Syntax);
            }

            if (temp != null)
            {
                FreeTemp(temp);
            }

            if (sequence != null)
            {
                FreeLocals(sequence, doNotRelease: null);
            }
        }

 private void EmitConstantSwitchHeader(BoundExpression expression, LabelSymbol target)
 {
     EmitExpression(expression, false);
     _builder.EmitBranch(ILOpCode.Br, target);
 }

        private static KeyValuePair<ConstantValue, object>[] GetSwitchCaseLabels(ImmutableArray<BoundSwitchSection> sections, ref LabelSymbol fallThroughLabel)
        {
            var labelsBuilder = ArrayBuilder<KeyValuePair<ConstantValue, object>>.GetInstance();
            foreach (var section in sections)
            {
                foreach (BoundSwitchLabel boundLabel in section.SwitchLabels)
                {
                    var label = boundLabel.Label;
                    if (boundLabel.ConstantValueOpt == null)
                    {
                        fallThroughLabel = label;
                    }
                    else
                    {
                        var value = boundLabel.ConstantValueOpt;
                        Debug.Assert(value != null
                            && SwitchConstantValueHelper.IsValidSwitchCaseLabelConstant(value));
                        labelsBuilder.Add(new KeyValuePair<ConstantValue, object>(value, label));
                    }
                }
            }

            return labelsBuilder.ToArrayAndFree();
        }

        private BoundBlock PendBranches(
            AwaitFinallyFrame frame,
            LocalSymbol pendingBranchVar,
            LabelSymbol finallyLabel)
        {
            var bodyStatements = ArrayBuilder<BoundStatement>.GetInstance();

            // handle proxy labels if have any
            var proxiedLabels = frame.proxiedLabels;
            var proxyLabels = frame.proxyLabels;

            // skip 0 - it means we took no explicit branches
            int i = 1;
            if (proxiedLabels != null)
            {
                for (int cnt = proxiedLabels.Count; i <= cnt; i++)
                {
                    var proxied = proxiedLabels[i - 1];
                    var proxy = proxyLabels[proxied];

                    PendBranch(bodyStatements, proxy, i, pendingBranchVar, finallyLabel);
                }
            }

            var returnProxy = frame.returnProxyLabel;
            if (returnProxy != null)
            {
                PendBranch(bodyStatements, returnProxy, i, pendingBranchVar, finallyLabel);
            }

            return _F.Block(bodyStatements.ToImmutableAndFree());
        }

        private BoundStatement MakeSwitchStatementWithNullableExpression(
            CSharpSyntaxNode syntax,
            BoundExpression rewrittenExpression,
            ImmutableArray<BoundSwitchSection> rewrittenSections,
            LabelSymbol constantTargetOpt,
            ImmutableArray<LocalSymbol> locals,
            GeneratedLabelSymbol breakLabel,
            BoundSwitchStatement oldNode)
        {
            Debug.Assert(rewrittenExpression.Type.IsNullableType());

            var exprSyntax = rewrittenExpression.Syntax;
            var exprNullableType = rewrittenExpression.Type;

            var statementBuilder = ArrayBuilder<BoundStatement>.GetInstance();

            // Rewrite the nullable expression to a temp as we might have a user defined conversion from source expression to switch governing type.
            // We can avoid generating the temp if the expression is a bound local.
            LocalSymbol tempLocal;
            if (rewrittenExpression.Kind != BoundKind.Local)
            {
                BoundAssignmentOperator assignmentToTemp;
                BoundLocal boundTemp = _factory.StoreToTemp(rewrittenExpression, out assignmentToTemp);
                var tempAssignment = new BoundExpressionStatement(exprSyntax, assignmentToTemp);
                statementBuilder.Add(tempAssignment);
                tempLocal = boundTemp.LocalSymbol;
                rewrittenExpression = boundTemp;
            }
            else
            {
                tempLocal = null;
            }

            // Generate a BoundConditionalGoto with null check as the conditional expression and appropriate switch label as the target: null, default or exit label.
            BoundStatement condGotoNullValueTargetLabel = new BoundConditionalGoto(
                exprSyntax,
                condition: MakeNullCheck(exprSyntax, rewrittenExpression, BinaryOperatorKind.NullableNullEqual),
                jumpIfTrue: true,
                label: GetNullValueTargetSwitchLabel(rewrittenSections, breakLabel));

            // Rewrite the switch statement using nullable expression's underlying value as the switch expression.

            // rewrittenExpression.GetValueOrDefault()
            MethodSymbol getValueOrDefault = GetNullableMethod(syntax, exprNullableType, SpecialMember.System_Nullable_T_GetValueOrDefault);
            BoundCall callGetValueOrDefault = BoundCall.Synthesized(exprSyntax, rewrittenExpression, getValueOrDefault);
            rewrittenExpression = callGetValueOrDefault;

            // rewrite switch statement
            BoundStatement rewrittenSwitchStatement = MakeSwitchStatementWithNonNullableExpression(
                syntax,
                condGotoNullValueTargetLabel,
                rewrittenExpression,
                rewrittenSections,
                constantTargetOpt,
                locals,
                breakLabel,
                oldNode);

            statementBuilder.Add(rewrittenSwitchStatement);

            return new BoundBlock(syntax, locals: (object)tempLocal == null ? ImmutableArray<LocalSymbol>.Empty : ImmutableArray.Create<LocalSymbol>(tempLocal), statements: statementBuilder.ToImmutableAndFree());
        }

 // called on branches and labels
 private void RecordBranch(LabelSymbol label)
 {
     DummyLocal dummy;
     if (_dummyVariables.TryGetValue(label, out dummy))
     {
         RecordVarRead(dummy);
     }
     else
     {
         // create a dummy and start tracing it
         dummy = new DummyLocal();
         _dummyVariables.Add(label, dummy);
         _locals.Add(dummy, new LocalDefUseInfo(StackDepth()));
         RecordVarWrite(dummy);
     }
 }

        private BoundStatement MakeSwitchStatementWithNonNullableExpression(
            CSharpSyntaxNode syntax,
            BoundStatement preambleOpt,
            BoundExpression rewrittenExpression,
            ImmutableArray<BoundSwitchSection> rewrittenSections,
            LabelSymbol constantTargetOpt,
            ImmutableArray<LocalSymbol> locals,
            GeneratedLabelSymbol breakLabel,
            BoundSwitchStatement oldNode)
        {
            Debug.Assert(!rewrittenExpression.Type.IsNullableType());
            Debug.Assert((object)oldNode.StringEquality == null);

            // If we are emitting a hash table based string switch,
            // we need to generate a helper method for computing
            // string hash value in <PrivateImplementationDetails> class.

            MethodSymbol stringEquality = null;
            if (rewrittenExpression.Type.SpecialType == SpecialType.System_String)
            {
                EnsureStringHashFunction(rewrittenSections, syntax);
                stringEquality = GetSpecialTypeMethod(syntax, SpecialMember.System_String__op_Equality);
            }

            return oldNode.Update(
                loweredPreambleOpt: preambleOpt,
                boundExpression: rewrittenExpression,
                constantTargetOpt: constantTargetOpt,
                innerLocals: locals,
                switchSections: rewrittenSections,
                breakLabel: breakLabel,
                stringEquality: stringEquality);
        }

        private BoundSwitchLabel BindSwitchSectionLabel(SwitchLabelSyntax node, Binder sectionBinder, LabelSymbol label, DiagnosticBag diagnostics)
        {
            var switchGoverningType = SwitchGoverningType;
            BoundExpression boundLabelExpressionOpt = null;
            ConstantValue labelExpressionConstant = null;

            // Prevent cascading diagnostics
            bool hasErrors = node.HasErrors;

            switch (node.Kind())
            {
                case SyntaxKind.CaseSwitchLabel:
                    var caseLabelSyntax = (CaseSwitchLabelSyntax)node;
                    // Bind the label case expression
                    boundLabelExpressionOpt = sectionBinder.BindValue(caseLabelSyntax.Value, diagnostics, BindValueKind.RValue);
                    boundLabelExpressionOpt = ConvertCaseExpression(caseLabelSyntax, boundLabelExpressionOpt, sectionBinder, ref labelExpressionConstant, diagnostics);

                    // Check for bind errors
                    hasErrors = hasErrors || boundLabelExpressionOpt.HasAnyErrors;

                    // SPEC:    The constant expression of each case label must denote a value that
                    // SPEC:    is implicitly convertible (§6.1) to the governing type of the switch statement.
                    if (!hasErrors && labelExpressionConstant == null)
                    {
                        diagnostics.Add(ErrorCode.ERR_ConstantExpected, caseLabelSyntax.Value.Location);
                        hasErrors = true;
                    }

                    if (!hasErrors && (object)labelExpressionConstant != null && FindMatchingSwitchCaseLabel(labelExpressionConstant, caseLabelSyntax) != label)
                    {
                        diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, labelExpressionConstant?.GetValueToDisplay() ?? label.Name);
                        hasErrors = true;
                    }

                    // LabelSymbols for all the switch case labels are created by BuildLabels().
                    // Fetch the matching switch case label symbols
                    break;
                case SyntaxKind.CasePatternSwitchLabel:
                    if (!node.HasErrors)
                    {
                        // This should not occur, because it would have been a syntax error
                        throw ExceptionUtilities.UnexpectedValue(node.Kind());
                    }
                    break;
                case SyntaxKind.DefaultSwitchLabel:
                    if (GetDefaultLabel() != label)
                    {
                        diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, label.Name);
                        hasErrors = true;
                    }
                    break;
                default:
                    throw ExceptionUtilities.UnexpectedValue(node.Kind());
            }

            return new BoundSwitchLabel(
                syntax: node,
                label: label,
                expressionOpt: boundLabelExpressionOpt,
                constantValueOpt: labelExpressionConstant,
                hasErrors: hasErrors);
        }

        private BoundPatternSwitchLabel BindPatternSwitchSectionLabel(
            Binder sectionBinder, BoundExpression boundSwitchExpression, SwitchLabelSyntax node, LabelSymbol label, ref BoundPatternSwitchLabel defaultLabel, DiagnosticBag diagnostics)
        {
            switch (node.Kind())
            {
                case SyntaxKind.CaseSwitchLabel:
                    {
                        var caseLabelSyntax = (CaseSwitchLabelSyntax)node;
                        bool wasExpression;
                        var pattern = sectionBinder.BindConstantPattern(
                            node, boundSwitchExpression, boundSwitchExpression.Type, caseLabelSyntax.Value, node.HasErrors, diagnostics, out wasExpression, wasSwitchCase: true);
                        bool hasErrors = pattern.HasErrors;
                        var constantValue = pattern.ConstantValue;
                        if (!hasErrors &&
                            (object)constantValue != null &&
                            pattern.Value.Type == SwitchGoverningType &&
                            this.FindMatchingSwitchCaseLabel(constantValue, caseLabelSyntax) != label)
                        {
                            diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, pattern.ConstantValue.GetValueToDisplay() ?? label.Name);
                            hasErrors = true;
                        }

                        // Until we've determined whether or not the switch label is reachable, we assume it
                        // is. The caller updates isReachable after determining if the label is subsumed.
                        const bool isReachable = true;
                        return new BoundPatternSwitchLabel(node, label, pattern, null, isReachable, hasErrors);
                    }

                case SyntaxKind.DefaultSwitchLabel:
                    {
                        var defaultLabelSyntax = (DefaultSwitchLabelSyntax)node;
                        var pattern = new BoundWildcardPattern(node);
                        bool hasErrors = pattern.HasErrors;
                        if (defaultLabel != null)
                        {
                            diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, label.Name);
                            hasErrors = true;
                        }

                        // We always treat the default label as reachable, even if the switch is complete.
                        const bool isReachable = true;

                        // Note that this is semantically last! The caller will place it in the decision tree
                        // in the final position.
                        defaultLabel = new BoundPatternSwitchLabel(node, label, pattern, null, isReachable, hasErrors);
                        return defaultLabel;
                    }

                case SyntaxKind.CasePatternSwitchLabel:
                    {
                        var matchLabelSyntax = (CasePatternSwitchLabelSyntax)node;
                        var pattern = sectionBinder.BindPattern(
                            matchLabelSyntax.Pattern, boundSwitchExpression, boundSwitchExpression.Type, node.HasErrors, diagnostics, wasSwitchCase: true);
                        return new BoundPatternSwitchLabel(node, label, pattern,
                            matchLabelSyntax.WhenClause != null ? sectionBinder.BindBooleanExpression(matchLabelSyntax.WhenClause.Condition, diagnostics) : null,
                            true, node.HasErrors);
                    }

                default:
                    throw ExceptionUtilities.UnexpectedValue(node);
            }
        }

 public BoundSwitchLabel(CSharpSyntaxNode syntax, LabelSymbol label, bool hasErrors = false)
     : this(syntax, label, expressionOpt: null, hasErrors: hasErrors)
 {
 }