public bool IsBranchTarget(ActionBlock block)
{
if (null == block)
{
throw new ArgumentNullException("block");
}
foreach (ActionBlock p in block.Predecessors)
{
switch (p.ActionType)
{
case ActionType.Branch:
BranchActionBlock br = (BranchActionBlock)p;
if (br.Target == block)
{
return(true);
}
break;
case ActionType.ConditionalBranch:
ConditionalBranchActionBlock cbr = (ConditionalBranchActionBlock)p;
if (cbr.Then == block)
{
return(true);
}
break;
}
}
return(false);
}
void ConnectActionBlocks()
{
for (int i = 0; i < _blocks.Count; ++i)
{
ActionBlock block = _blocks [i];
switch (block.ActionType)
{
case ActionType.Branch:
BranchActionBlock br = (BranchActionBlock)block;
br.SetTarget(GetBranchTarget(br.SourceInstruction));
break;
case ActionType.ConditionalBranch:
ConditionalBranchActionBlock cbr = (ConditionalBranchActionBlock)block;
cbr.SetTargets(GetBranchTarget(cbr.SourceInstruction), GetBlockAtOrNull(i + 1));
break;
case ActionType.Return:
break;
default:
AbstractFallThroughActionBlock ftb = (AbstractFallThroughActionBlock)block;
ftb.SetNext(GetBlockAtOrNull(i + 1));
break;
}
}
}
void SimplifyActionBlocks()
{
int index = 0;
while (index < _blocks.Count)
{
ActionBlock block = _blocks [index];
switch (block.ActionType)
{
case ActionType.ConditionalBranch:
// if condition goto label
// return expression
// label: return true
// |
// V
// return (condition || expression)
//
// label: return false
// |
// V
// return (!condition || expression)
ConditionalBranchActionBlock cbr = (ConditionalBranchActionBlock)block;
if (IsReturnTrueOrFalse(cbr.Then) &&
IsReturn(cbr.Else) &&
1 == cbr.Then.Predecessors.Count &&
1 == cbr.Else.Predecessors.Count)
{
BinaryOperator op = BinaryOperator.LogicalOr;
Expression lhs = cbr.Condition;
Expression rhs = ((ReturnActionBlock)cbr.Else).Expression;
if (((LiteralExpression)((ReturnActionBlock)cbr.Then).Expression).Value.Equals(0))
{
op = BinaryOperator.LogicalAnd;
_expressionDecompiler.Negate(lhs);
lhs = _expressionDecompiler.Pop();
}
ActionBlock newBlock = new ReturnActionBlock(
block.SourceInstruction,
new BinaryExpression(op, lhs, rhs));
_graph.ReplaceAt(index, newBlock);
index = 0;
continue;
}
break;
}
++index;
}
}
private ActionBlock OnConditionalBranch(ConditionalBranchActionBlock block)
{
throw new QueryOptimizationException();
}
void WriteConditionalBranch (ActionFlowGraph afg, ConditionalBranchActionBlock block)
{
_writer.Write ("if ");
WriteExpression (block.Condition);
_writer.Write (' ');
WriteGoto (afg, block.Then);
}
