private LatticeCell EvaluateInstruction(
Instruction instruction,
IReadOnlyDictionary <ValueTag, LatticeCell> cells,
FlowGraph graph)
{
if (instruction.Prototype is CopyPrototype)
{
// Special case on copy instructions because they're
// easy to deal with: just return the lattice cell for
// the argument.
return(GetCellForValue(instruction.Arguments[0], cells));
}
var foundTop = false;
var args = new Constant[instruction.Arguments.Count];
for (int i = 0; i < args.Length; i++)
{
var argCell = GetCellForValue(instruction.Arguments[i], cells);
if (argCell.Kind == LatticeCellKind.Top)
{
// We can't evaluate this value *yet*. Keep looking
// for bottom argument cells and set a flag to record
// that this value cannot be evaluated yet.
foundTop = true;
}
else if (argCell.Kind == LatticeCellKind.Constant)
{
// Yay. We found a compile-time constant.
args[i] = argCell.Value;
}
else
{
// We can't evaluate this value at compile-time
// because one if its arguments is unknown.
// Time to early-out.
return(EvaluateNonConstantInstruction(instruction, graph));
}
}
if (foundTop)
{
// We can't evaluate this value yet.
return(LatticeCell.Top);
}
else
{
// Evaluate the instruction.
var constant = Evaluate(instruction.Prototype, args);
if (constant == null)
{
// Turns out we can't evaluate the instruction. But maybe
// we can say something sensible about its nullability?
return(EvaluateNonConstantInstruction(instruction, graph));
}
else
{
return(LatticeCell.Constant(constant));
}
}
}
