private void ConnectBlock(BasicBlock block)
{
var cil = block.LastInstruction;
switch (block.FlowControl) {
case FlowControl.Branch:
case FlowControl.Cond_Branch:
ConnectBranch(block);
break;
case FlowControl.Call:
case FlowControl.Next:
if (cil.Next != null) {
this.graph.Connect(block, GetBlock(cil.Next));
}
break;
case FlowControl.Return:
case FlowControl.Throw:
break;
default:
throw new NotSupportedException();
}
}
private void RegisterBlock(BasicBlock block)
{
blocks.Add(block.FirstInstruction.Offset, block);
}
private BasicBlock MarkBlockStart(Instruction cil)
{
var block = GetBlock(cil);
if (block == null) {
block = new BasicBlock(this.body.Method);
block.Instructions.Add(cil);
RegisterBlock(block);
}
return block;
}
private BasicBlock[] GetBranchTargetsBlocks(Instruction cil)
{
var targets = GetBranchTargets(cil);
var blocks = new BasicBlock[targets.Length];
for (int i = 0; i < targets.Length; i++) {
blocks[i] = GetBlock(targets[i]);
}
return blocks;
}
private bool WriteBasicBlock(BasicBlock block, List<CodeStatement> stmts)
{
foreach (var stmt in block.Statements) {
AddStatement(stmts, stmt);
}
if (block.FlowControl == FlowControl.Return ||
block.FlowControl == FlowControl.Throw) {
var lastReturn = stmts.LastOrDefault() as CodeReturnStatement;
if (lastReturn != null) {
var lastAssignment = lastReturn.Previous as CodeAssignStatement;
if (lastAssignment != null) {
var lhsVariable = lastAssignment.Left as CodeVariableReference;
var rhsVariable = lastReturn.Expression as CodeVariableReference;
if (lhsVariable != null && rhsVariable != null && lhsVariable.Variable == rhsVariable.Variable) {
lastReturn.Previous = lastAssignment.Previous;
stmts.Remove(lastAssignment);
lastReturn.Expression = lastAssignment.Right;
}
}
}
return true;
}
return false;
}
private bool WriteWhileLoop(BasicBlock block, Loop loop, List<CodeStatement> stmts, Context context)
{
var loopContext = context.NewLoop(loop);
CodeWhileStatement whileStmt;
if (block.Statements.Count > 1) {
// emit a while(true) { $bb.stmts; if($condition) { $then_stmts; break; } ... }
whileStmt = new CodeWhileStatement {
TestExpression = new CodePrimitiveExpression(true)
};
var conditional = new Conditional(this.graph, block);
WriteIf(block, conditional, whileStmt.Statements, loopContext);
}
else {
var last = (CodeExpressionStatement)block.Statements.Last();
var test = last.Expression;
if (block.ElseEdge == loop.Follow) {
test = test.Invert();
}
// emit a pre-tested loop
whileStmt = new CodeWhileStatement {
TestExpression = test
};
}
AddStatement(stmts, whileStmt);
if (!loop.Tails.Contains(block)) {
WriteLoopInner(block, loop, whileStmt.Statements, loopContext);
}
if (loop.Follow != null) {
return WriteCode(null, (BasicBlock)loop.Follow, stmts, context);
}
return false;
}
private bool WriteTry(BasicBlock block, List<CodeStatement> stmts, Context context)
{
// find catch/finally blocks that match this try
// write this block into the try
// continue until we find the try follow, which is the first block that has a last != leave
// if the try follow lands on a loop or conditional header, then use their follow instead
// TODO: deal with nested trys
var tryStmt = new CodeTryStatement();
AddStatement(stmts, tryStmt);
var tryContext = context.NewTry(block.Try);
WriteCode(null, block, tryStmt.Try, tryContext);
foreach (BasicBlock catchBlock in block.Try.Catches) {
var catchType = catchBlock.ExceptionHandler.CatchType;
var variable = Interpreter.CreateExceptionVariableReference(this.method.Definition, catchType);
var catchClause = new CodeCatchClause {
Type = new CodeTypeReference(catchType),
Variable = variable
};
tryStmt.Catches.Add(catchClause);
WriteCode(null, catchBlock, catchClause.Statements, tryContext);
}
if (block.Try.Finally != null) {
WriteCode(null, (BasicBlock)block.Try.Finally, tryStmt.Finally, tryContext);
}
if (block.Try.Follow != null) {
return WriteCode(block, (BasicBlock)block.Try.Follow, stmts, context);
}
return true;
}
public void ProcessBlock(BasicBlock block)
{
this.block = block;
if (this.block.ExceptionHandler != null &&
this.block.ExceptionHandler.TryStart.Offset != this.block.FirstInstruction.Offset &&
this.block.ExceptionHandler.HandlerType == ExceptionHandlerType.Catch) {
Debug.Assert(!this.stack.Any());
// this is a catch handler
// the exception object is expected to be sitting on the top of the stack
// on entry to the catch block
var catchType = this.block.ExceptionHandler.CatchType;
var catchTypeDef = catchType.Resolve();
this.ExternalMethods.Add(catchTypeDef.Methods.Where(x => x.IsConstructor).First());
var exception = CreateExceptionVariableReference(this.method, catchType);
Push(exception);
}
foreach (var cil in block.Instructions) {
HandleInstruction(cil);
}
// In debug builds, the compiler emits CIL that helps the debugger with locality,
// but screws up the stack because we assume that each block defines a stack boundry.
// That is, at the start and end of each block, the stack is assumed to be empty.
// This is an attempt to have instructions that cause the stack to become empty be
// consumed by the predecessors that need them in order to make this assumption true.
// Another case occurs when the compiler decides to push a value in one block
// and then pop it in another.
// This new strategy involves creating temporary register variables that can
// be used to transfer extra stack values from one block to another.
if (this.stack.Any()) {
StashStackExtras(block);
}
}
private bool WriteRepeatLoop(BasicBlock block, Loop loop, List<CodeStatement> stmts, Context context)
{
var loopContext = context.NewLoop(loop);
var last = (CodeExpressionStatement)block.Statements.Last();
var test = last.Expression;
CodeRepeatStatement repeatStmt = new CodeRepeatStatement {
TestExpression = test
};
AddStatement(stmts, repeatStmt);
if (!loop.Tails.Contains(block)) {
WriteLoopInner(block, loop, repeatStmt.Statements, loopContext);
}
var preTestStmts = block.Statements.Take(block.Statements.Count - 1);
repeatStmt.Statements.AddRange(preTestStmts);
if (loop.Follow != null) {
return WriteCode(null, (BasicBlock)loop.Follow, stmts, context);
}
return false;
}
private void WriteLoopInner(BasicBlock block, Loop loop, List<CodeStatement> stmts, Context context)
{
Node succ;
if (block.Successors.Count > 1) {
succ = block.ThenEdge;
if (succ == loop.Follow) {
succ = block.ElseEdge;
}
}
else {
succ = block.Successors.First();
}
WriteCode(block, (BasicBlock)succ, stmts, context);
}
private bool WriteLoop(BasicBlock block, List<CodeStatement> stmts, Context context)
{
var loop = block.Loop;
Debug.Assert(loop.Header == block);
switch (loop.LoopType) {
case LoopType.While:
return WriteWhileLoop(block, loop, stmts, context);
case LoopType.Repeat:
return WriteRepeatLoop(block, loop, stmts, context);
case LoopType.Endless:
return WriteEndlessLoop(block, loop, stmts, context);
default:
throw new InvalidOperationException();
}
}
private bool WriteIf(BasicBlock block, Conditional conditional, List<CodeStatement> stmts, Context context)
{
var preStmts = block.Statements.Take(block.Statements.Count - 1);
AddManyStatements(stmts, preStmts);
var last = (CodeExpressionStatement)block.Statements.Last();
var ifStmt = new CodeIfStatement {
Condition = last.Expression
};
AddStatement(stmts, ifStmt);
bool emptyThen = false;
// is there a follow?
if (conditional.Follow != null && conditional.Follow != context.LoopFollow) {
// process the THEN part
bool isBreak = false;
var succ = block.ThenEdge;
if (succ.DfsTraversed != DfsTraversal.Alpha) {
if (succ != conditional.Follow) {
// THEN part
ifStmt.Condition = ifStmt.Condition.Invert();
isBreak = WriteCode(block, (BasicBlock)succ, ifStmt.TrueStatements, context.NewUntil(conditional.Follow));
}
else {
// empty THEN part => negate ELSE part
isBreak = WriteCode(block, (BasicBlock)block.ElseEdge, ifStmt.TrueStatements, context.NewUntil(conditional.Follow));
emptyThen = true;
}
}
// process the ELSE part
succ = block.ElseEdge;
if (succ.DfsTraversed != DfsTraversal.Alpha) {
if (succ != conditional.Follow) {
// ELSE part
List<CodeStatement> output;
if (isBreak)
output = stmts;
else
output = ifStmt.FalseStatements;
isBreak = WriteCode(block, (BasicBlock)succ, output, context.NewUntil(conditional.Follow));
if (block == conditional.Follow)
return isBreak;
}
}
else if (!emptyThen) {
// already visited => emit label
throw new InvalidOperationException();
}
// Continue with the follow
return WriteCode(null, (BasicBlock)conditional.Follow, stmts, context);
}
else {
// no follow => if..then..else
ifStmt.Condition = ifStmt.Condition.Invert();
var isBreak = WriteCode(block, (BasicBlock)block.ThenEdge, ifStmt.TrueStatements, context);
var output = ifStmt.FalseStatements;
if (isBreak)
output = stmts;
return WriteCode(block, (BasicBlock)block.ElseEdge, output, context);
}
}
private bool WriteEndlessLoop(BasicBlock block, Loop loop, List<CodeStatement> stmts, Context context)
{
var loopContext = context.NewLoop(loop);
CodeWhileStatement whileStmt = new CodeWhileStatement {
TestExpression = new CodePrimitiveExpression(true)
};
AddStatement(stmts, whileStmt);
if (block.Successors.Count > 1) {
var conditional = new Conditional(this.graph, block);
WriteIf(block, conditional, whileStmt.Statements, loopContext);
}
else {
WriteBasicBlock(block, whileStmt.Statements);
}
if (!loop.Tails.Contains(block)) {
WriteLoopInner(block, loop, whileStmt.Statements, loopContext);
}
if (loop.Follow != null) {
return WriteCode(null, (BasicBlock)loop.Follow, stmts, context);
}
return false;
}
private bool WriteCode(BasicBlock previous, BasicBlock block, List<CodeStatement> stmts, Context context)
{
if (block == context.LoopFollow) {
AddStatement(stmts, new CodeBreakStatement());
return true;
}
if (block == context.LoopHeader && (previous == null || !previous.IsLoopLatch)) {
AddStatement(stmts, new CodeContinueStatement());
return true;
}
if (context.IsUntil(block) ||
block.DfsTraversed == DfsTraversal.Alpha) {
return false;
}
if (block.IsTryHeader && context.Try != block.Try) {
return WriteTry(block, stmts, context);
}
block.DfsTraversed = DfsTraversal.Alpha;
if (block.IsLoopHeader) {
return WriteLoop(block, stmts, context);
}
else if (block.IsMultiWay) {
return WriteSwitch(block, stmts, context);
}
else if (block.Conditional != null) {
return WriteIf(block, block.Conditional, stmts, context);
}
else {
var isReturn = WriteBasicBlock(block, stmts);
if (isReturn)
return true;
var succ = (BasicBlock)block.Successors.FirstOrDefault();
return WriteCode(block, succ, stmts, context);
}
}
private bool WriteSwitch(BasicBlock block, List<CodeStatement> stmts, Context context)
{
AddManyStatements(stmts, block.Statements);
var switchStmt = (CodeSwitchStatement)block.Statements.Last();
var targets = (Instruction[])block.LastInstruction.Operand;
var casesByOffset = new Dictionary<int, CodeCase>();
var follow = block.Conditional.Follow;
foreach (BasicBlock succ in block.Successors) {
CodeCase codeCase = new CodeCase();
if (succ.DfsTraversed != DfsTraversal.Alpha) {
var followContext = context;
if (follow != null) {
followContext = context.NewUntil(follow);
}
if (!WriteCode(block, succ, codeCase.Statements, followContext)) {
codeCase.Statements.Add(new CodeBreakStatement());
}
}
casesByOffset.Add(succ.BeginOffset, codeCase);
}
for (int i = 0; i < targets.Length; i++) {
int offset = targets[i].Offset;
var codeCase = casesByOffset[offset];
codeCase.Expressions.Add(new CodePrimitiveExpression(i));
}
switchStmt.Cases.AddRange(casesByOffset.Values);
if (follow != null) {
return WriteCode(null, (BasicBlock)follow, stmts, context);
}
return false;
}
private void ConnectBranch(BasicBlock block)
{
var cil = block.LastInstruction;
if (cil.IsMultiWay()) {
var blocks = GetBranchTargetsBlocks(cil);
if (cil.Next != null) {
this.graph.Connect(block, GetBlock(cil.Next));
}
foreach (var target in blocks) {
this.graph.Connect(block, target);
}
}
else {
var target = GetBranchTargetBlock(cil);
if (block.FlowControl == FlowControl.Cond_Branch && cil.Next != null) {
this.graph.Connect(block, GetBlock(cil.Next));
}
this.graph.Connect(block, target);
}
}
private void StashStackExtras(BasicBlock block)
{
var items = this.stack.Reverse();
foreach (var item in items) {
var lhs = block.PushStash(this.typeSystem, item);
var stmt = new CodeAssignStatement(lhs, item.Expression);
this.block.Statements.Insert(item.Index, stmt);
}
this.stack.Clear();
}
