/// <inheritdoc />
public void Rewrite(MethodDefinition methodDefinition, ILProcessor il, ObserverRewriterContext context)
{
List <Instruction> branches = GetBranchingOps(methodDefinition).ToList();
List <Instruction> branchTos = branches.Select(x => (Instruction)x.Operand).ToList();
// Start from 2 because we setup Observer in first 2 instructions
int position = 2;
List <CodeSegment> segments = new List <CodeSegment>();
var codeSegment = new CodeSegment(methodDefinition);
while (position < methodDefinition.Body.Instructions.Count)
{
Instruction instruction = methodDefinition.Body.Instructions[position];
// End of a segment. Add this as the last instruction and move onwards with a new segment
if (branches.Contains(instruction))
{
codeSegment.Instructions.Add(instruction);
segments.Add(codeSegment);
codeSegment = new CodeSegment(methodDefinition);
}
// Start of a new segment. End last segment and start new one with this as the first instruction
else if (branchTos.Contains(instruction))
{
if (codeSegment.Instructions.Any())
{
segments.Add(codeSegment);
}
codeSegment = new CodeSegment(methodDefinition);
codeSegment.Instructions.Add(instruction);
}
// Just an in-between instruction. Add to current segment.
else
{
codeSegment.Instructions.Add(instruction);
}
position++;
}
// Got to end of the method. Add the last one if necessary
if (!segments.Contains(codeSegment) && codeSegment.Instructions.Any())
{
segments.Add(codeSegment);
}
foreach (CodeSegment segment in segments)
{
AddSpendGasMethodBeforeInstruction(il, context.Observer, context.ObserverVariable, segment);
}
// All of the branches now need to point to the place 3 instructions earlier!
foreach (Instruction branch in branches)
{
Instruction currentlyPointingTo = (Instruction)branch.Operand;
branch.Operand = currentlyPointingTo.Previous.Previous.Previous;
}
}
/// <summary>
/// Adds a call to SpendGas from the RuntimeObserver before the given instruction.
/// </summary>
private static void AddSpendGasMethodBeforeInstruction(ILProcessor il, ObserverReferences observer, VariableDefinition variable, CodeSegment codeSegment)
{
Instruction first = codeSegment.Instructions.First();
Instruction newFirst = il.CreateLdlocBest(variable);
long segmentCost = (long)codeSegment.CalculateGasCost().Value;
il.Body.SimplifyMacros();
il.InsertBefore(first, newFirst); // load observer
il.InsertBefore(first, il.Create(OpCodes.Ldc_I8, (long)segmentCost)); // load gas amount
il.InsertBefore(first, il.Create(OpCodes.Call, observer.SpendGasMethod)); // trigger method
il.Body.OptimizeMacros();
}