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Simplify ControlFlowGraph.Build. #172

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Simplify ControlFlowGraph.Build. #172

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f3abb7b
Simplify `ControlFlowGraph.Build`.
mykolav Jan 6, 2021
5874c55
Simplify `ControlFlowGraph.Build`.
mykolav Feb 13, 2021
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75 changes: 36 additions & 39 deletions src/Minsk/CodeAnalysis/Binding/ControlFlowGraph.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -138,7 +138,6 @@ private void EndBlock()

public sealed class GraphBuilder
{
private Dictionary<BoundStatement, BasicBlock> _blockFromStatement = new Dictionary<BoundStatement, BasicBlock>();
private Dictionary<BoundLabel, BasicBlock> _blockFromLabel = new Dictionary<BoundLabel, BasicBlock>();
private List<BasicBlockBranch> _branches = new List<BasicBlockBranch>();
private BasicBlock _start = new BasicBlock(isStart: true);
Expand All @@ -153,52 +152,50 @@ public ControlFlowGraph Build(List<BasicBlock> blocks)

foreach (var block in blocks)
{
foreach (var statement in block.Statements)
{
_blockFromStatement.Add(statement, block);
if (statement is BoundLabelStatement labelStatement)
_blockFromLabel.Add(labelStatement.Label, block);
}
var firstStatement = block.Statements.FirstOrDefault();
// By definition, only the first statement of a basic block
// can be of the type BoundLabelStatement.
if (firstStatement is BoundLabelStatement labelStatement)
_blockFromLabel.Add(labelStatement.Label, block);
}

for (int i = 0; i < blocks.Count; i++)
{
var current = blocks[i];
var next = i == blocks.Count - 1 ? _end : blocks[i + 1];

foreach (var statement in current.Statements)
var lastStatement = current.Statements.Last();
// By definition, only the last statement of a basic block
// can be a branching/return statement.
// In other words, only a basic block's last statement can be outgoing.
switch (lastStatement.Kind)
{
var isLastStatementInBlock = statement == current.Statements.Last();
switch (statement.Kind)
{
case BoundNodeKind.GotoStatement:
var gs = (BoundGotoStatement)statement;
var toBlock = _blockFromLabel[gs.Label];
Connect(current, toBlock);
break;
case BoundNodeKind.ConditionalGotoStatement:
var cgs = (BoundConditionalGotoStatement)statement;
var thenBlock = _blockFromLabel[cgs.Label];
var elseBlock = next;
var negatedCondition = Negate(cgs.Condition);
var thenCondition = cgs.JumpIfTrue ? cgs.Condition : negatedCondition;
var elseCondition = cgs.JumpIfTrue ? negatedCondition : cgs.Condition;
Connect(current, thenBlock, thenCondition);
Connect(current, elseBlock, elseCondition);
break;
case BoundNodeKind.ReturnStatement:
Connect(current, _end);
break;
case BoundNodeKind.NopStatement:
case BoundNodeKind.VariableDeclaration:
case BoundNodeKind.LabelStatement:
case BoundNodeKind.ExpressionStatement:
if (isLastStatementInBlock)
Connect(current, next);
break;
default:
throw new Exception($"Unexpected statement: {statement.Kind}");
}
case BoundNodeKind.GotoStatement:
var gs = (BoundGotoStatement)lastStatement;
var toBlock = _blockFromLabel[gs.Label];
Connect(current, toBlock);
break;
case BoundNodeKind.ConditionalGotoStatement:
var cgs = (BoundConditionalGotoStatement)lastStatement;
var thenBlock = _blockFromLabel[cgs.Label];
var elseBlock = next;
var negatedCondition = Negate(cgs.Condition);
var thenCondition = cgs.JumpIfTrue ? cgs.Condition : negatedCondition;
var elseCondition = cgs.JumpIfTrue ? negatedCondition : cgs.Condition;
Connect(current, thenBlock, thenCondition);
Connect(current, elseBlock, elseCondition);
break;
case BoundNodeKind.ReturnStatement:
Connect(current, _end);
break;
case BoundNodeKind.NopStatement:
case BoundNodeKind.VariableDeclaration:
case BoundNodeKind.LabelStatement:
case BoundNodeKind.ExpressionStatement:
Connect(current, next);
break;
default:
throw new Exception($"Unexpected statement: {lastStatement.Kind}");
}
}

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