C# Block.FlowsTo方法代码示例

        public object VisitScriptBlock(ScriptBlockAst scriptBlockAst)
        {
            _currentBlock = _entryBlock;

            if (scriptBlockAst.DynamicParamBlock != null)
            {
                scriptBlockAst.DynamicParamBlock.Accept(this);
            }

            if (scriptBlockAst.BeginBlock != null)
            {
                scriptBlockAst.BeginBlock.Accept(this);
            }
            if (scriptBlockAst.ProcessBlock != null)
            {
                scriptBlockAst.ProcessBlock.Accept(this);
            }
            if (scriptBlockAst.EndBlock != null)
            {
                scriptBlockAst.EndBlock.Accept(this);
            }

            _currentBlock.FlowsTo(_exitBlock);

            return null;
        }

        public object VisitBinaryExpression(BinaryExpressionAst binaryExpressionAst)
        {
            if (binaryExpressionAst.Operator == TokenKind.And || binaryExpressionAst.Operator == TokenKind.Or)
            {
                // Logical and/or are short circuit operators, so we need to simulate the control flow.  The
                // left operand is always evaluated, visit it's expression in the current block.
                binaryExpressionAst.Left.Accept(this);

                // The right operand is conditionally evaluated.  We aren't generating any code here, just
                // modeling the flow graph, so we just visit the right operand in a new block, and have
                // both the current and new blocks both flow to a post-expression block.
                var targetBlock = new Block();
                var nextBlock = new Block();
                _currentBlock.FlowsTo(targetBlock);
                _currentBlock.FlowsTo(nextBlock);
                _currentBlock = nextBlock;

                binaryExpressionAst.Right.Accept(this);

                _currentBlock.FlowsTo(targetBlock);
                _currentBlock = targetBlock;
            }
            else
            {
                binaryExpressionAst.Left.Accept(this);
                binaryExpressionAst.Right.Accept(this);
            }

            return null;
        }

        private Tuple<Type, Dictionary<string, int>> AnalyzeImpl(TrapStatementAst trap)
        {
            _variables = FindAllVariablesVisitor.Visit(trap);

            // We disable optimizations for trap because it simplifies what we need to do when invoking
            // the trap, and it's assumed that the code inside a trap rarely, if ever, actually creates
            // any local variables.
            _disableOptimizations = true;
            Init();

            _localsAllocated = SpecialVariables.AutomaticVariables.Length;
            _currentBlock = _entryBlock;
            trap.Body.Accept(this);
            _currentBlock.FlowsTo(_exitBlock);

            return FinishAnalysis();
        }

        public object VisitTryStatement(TryStatementAst tryStatementAst)
        {
            // We don't attempt to accurately model flow in a try catch because every statement
            // can flow to each catch.  Instead, we'll assume the try block is not executed (because the very first statement
            // may throw), and have the data flow assume the block before the try is all that can reach the catches and finally.

            var blockBeforeTry = _currentBlock;
            _currentBlock = new Block();
            blockBeforeTry.FlowsTo(_currentBlock);

            tryStatementAst.Body.Accept(this);

            Block lastBlockInTry = _currentBlock;
            var finallyFirstBlock = tryStatementAst.Finally == null ? null : new Block();
            Block finallyLastBlock = null;

            // This is the first block after all the catches and finally (if present).
            var afterTry = new Block();

            bool isCatchAllPresent = false;

            foreach (var catchAst in tryStatementAst.CatchClauses)
            {
                if (catchAst.IsCatchAll)
                {
                    isCatchAllPresent = true;
                }

                // Any statement in the try block could throw and reach the catch, so assume the worst (from a data
                // flow perspective) and make the predecessor to the catch the block before entering the try.
                _currentBlock = new Block();
                blockBeforeTry.FlowsTo(_currentBlock);
                catchAst.Accept(this);
                _currentBlock.FlowsTo(finallyFirstBlock ?? afterTry);
            }

            if (finallyFirstBlock != null)
            {
                lastBlockInTry.FlowsTo(finallyFirstBlock);

                _currentBlock = finallyFirstBlock;
                tryStatementAst.Finally.Accept(this);
                _currentBlock.FlowsTo(afterTry);

                finallyLastBlock = _currentBlock;

                // For finally block, there are 2 cases: when try-body throw and when it doesn't.
                // For these two cases value of 'finallyLastBlock._throws' would be different.
                if (!isCatchAllPresent)
                {
                    // This flow exist only, if there is no catch for all exceptions.
                    blockBeforeTry.FlowsTo(finallyFirstBlock);

                    var rethrowAfterFinallyBlock = new Block();
                    finallyLastBlock.FlowsTo(rethrowAfterFinallyBlock);
                    rethrowAfterFinallyBlock._throws = true;
                    rethrowAfterFinallyBlock.FlowsTo(_exitBlock);
                }

                // This flow always exists.
                finallyLastBlock.FlowsTo(afterTry);
            }
            else
            {
                lastBlockInTry.FlowsTo(afterTry);
            }

            _currentBlock = afterTry;

            return null;
        }

        private void GenerateDoLoop(LoopStatementAst loopStatement)
        {
            // We model the flow graph like this:
            //    :RepeatTarget
            //       loop body
            //       // break -> goto BreakTarget
            //       // continue -> goto ContinueTarget
            //    :ContinueTarget
            //    if (condition)
            //    {
            //        goto RepeatTarget
            //    }
            //    :BreakTarget

            var continueBlock = new Block();
            var bodyBlock = new Block();
            var breakBlock = new Block();
            var gotoRepeatTargetBlock = new Block();

            _loopTargets.Add(new LoopGotoTargets(loopStatement.Label ?? "", breakBlock, continueBlock));

            _currentBlock.FlowsTo(bodyBlock);
            _currentBlock = bodyBlock;

            loopStatement.Body.Accept(this);

            _currentBlock.FlowsTo(continueBlock);
            _currentBlock = continueBlock;

            loopStatement.Condition.Accept(this);

            _currentBlock.FlowsTo(breakBlock);
            _currentBlock.FlowsTo(gotoRepeatTargetBlock);

            _currentBlock = gotoRepeatTargetBlock;
            _currentBlock.FlowsTo(bodyBlock);

            _currentBlock = breakBlock;

            _loopTargets.RemoveAt(_loopTargets.Count - 1);
        }

        private void GenerateWhileLoop(string loopLabel,
                                       Action generateCondition,
                                       Action generateLoopBody,
                                       Ast continueAction = null)
        {
            // We model the flow graph like this (if continueAction is null, the first part is slightly different):
            //    goto L
            //    :ContinueTarget
            //        continueAction
            //    :L
            //    if (condition)
            //    {
            //        loop body
            //        // break -> goto BreakTarget
            //        // continue -> goto ContinueTarget
            //        goto ContinueTarget
            //    }
            //    :BreakTarget

            var continueBlock = new Block();

            if (continueAction != null)
            {
                var blockAfterContinue = new Block();

                // Represent the goto over the condition before the first iteration.
                _currentBlock.FlowsTo(blockAfterContinue);

                _currentBlock = continueBlock;
                continueAction.Accept(this);

                _currentBlock.FlowsTo(blockAfterContinue);
                _currentBlock = blockAfterContinue;
            }
            else
            {
                _currentBlock.FlowsTo(continueBlock);
                _currentBlock = continueBlock;
            }

            var bodyBlock = new Block();
            var breakBlock = new Block();

            // Condition can be null from an uncommon for loop: for() {}
            if (generateCondition != null)
            {
                generateCondition();
                _currentBlock.FlowsTo(breakBlock);
            }

            _loopTargets.Add(new LoopGotoTargets(loopLabel ?? "", breakBlock, continueBlock));
            _currentBlock.FlowsTo(bodyBlock);
            _currentBlock = bodyBlock;
            generateLoopBody();
            _currentBlock.FlowsTo(continueBlock);

            _currentBlock = breakBlock;

            _loopTargets.RemoveAt(_loopTargets.Count - 1);
        }

        public object VisitSwitchStatement(SwitchStatementAst switchStatementAst)
        {
            var details = _variables[[email protected]];
            if (details.LocalTupleIndex == VariableAnalysis.Unanalyzed && !_disableOptimizations)
            {
                details.LocalTupleIndex = _localsAllocated++;
            }

            Action generateCondition = () =>
            {
                switchStatementAst.Condition.Accept(this);

                // $switch is set after evaluating the condition.
                _currentBlock.AddAst(new AssignmentTarget([email protected], typeof(IEnumerator)));
            };

            Action switchBodyGenerator = () =>
            {
                bool hasDefault = (switchStatementAst.Default != null);
                Block afterStmt = new Block();

                int clauseCount = switchStatementAst.Clauses.Count;
                for (int i = 0; i < clauseCount; i++)
                {
                    var clause = switchStatementAst.Clauses[i];
                    Block clauseBlock = new Block();
                    bool isLastClause = (i == (clauseCount - 1) && !hasDefault);
                    Block nextBlock = isLastClause ? afterStmt : new Block();

                    clause.Item1.Accept(this);

                    _currentBlock.FlowsTo(nextBlock);
                    _currentBlock.FlowsTo(clauseBlock);
                    _currentBlock = clauseBlock;

                    clause.Item2.Accept(this);

                    if (!isLastClause)
                    {
                        _currentBlock.FlowsTo(nextBlock);
                        _currentBlock = nextBlock;
                    }
                }

                if (hasDefault)
                {
                    // If any clause was executed, we skip the default, so there is always a branch over the default.
                    _currentBlock.FlowsTo(afterStmt);
                    switchStatementAst.Default.Accept(this);
                }

                _currentBlock.FlowsTo(afterStmt);
                _currentBlock = afterStmt;
            };

            GenerateWhileLoop(switchStatementAst.Label, generateCondition, switchBodyGenerator);

            return null;
        }

        public object VisitIfStatement(IfStatementAst ifStmtAst)
        {
            Block afterStmt = new Block();

            if (ifStmtAst.ElseClause == null)
            {
                // There is no else, flow can go straight to afterStmt.
                _currentBlock.FlowsTo(afterStmt);
            }

            int clauseCount = ifStmtAst.Clauses.Count;
            for (int i = 0; i < clauseCount; i++)
            {
                var clause = ifStmtAst.Clauses[i];
                bool isLastClause = (i == (clauseCount - 1) && ifStmtAst.ElseClause == null);
                Block clauseBlock = new Block();
                Block nextBlock = isLastClause ? afterStmt : new Block();

                clause.Item1.Accept(this);

                _currentBlock.FlowsTo(clauseBlock);
                _currentBlock.FlowsTo(nextBlock);
                _currentBlock = clauseBlock;

                clause.Item2.Accept(this);

                _currentBlock.FlowsTo(afterStmt);
                _currentBlock = nextBlock;
            }

            if (ifStmtAst.ElseClause != null)
            {
                ifStmtAst.ElseClause.Accept(this);
                _currentBlock.FlowsTo(afterStmt);
            }

            _currentBlock = afterStmt;
            return null;
        }