/// <summary>
/// Analyzes the tail end (last two instructions) of a block.
/// </summary>
/// <remarks>
/// Sets <c>switchVar</c> and <c>defaultInstruction</c> if they are null,
/// and adds found sections to <c>sectionLabels</c> and <c>sectionInstructions</c>.
///
/// If the function returns false, <c>sectionLabels</c> and <c>sectionInstructions</c> are unmodified.
/// </remarks>
/// <param name="block">The block to analyze.</param>
/// <param name="inputValues">The possible values of the "interesting" variable
/// when control flow reaches this block.</param>
/// <param name="tailOnly">If true, analyze only the tail (last two instructions).
/// If false, analyze the whole block.</param>
bool AnalyzeBlock(Block block, LongSet inputValues, bool tailOnly = false)
{
if (tailOnly)
{
Debug.Assert(block == rootBlock);
if (block.Instructions.Count < 2)
{
return(false);
}
}
else
{
Debug.Assert(switchVar != null); // switchVar should always be determined by the top-level call
if (block.IncomingEdgeCount != 1 || block == rootBlock)
{
return(false); // for now, let's only consider if-structures that form a tree
}
if (block.Instructions.Count != 2)
{
return(false);
}
if (block.Parent != rootBlock.Parent)
{
return(false); // all blocks should belong to the same container
}
}
var inst = block.Instructions[block.Instructions.Count - 2];
ILInstruction condition, trueInst;
LongSet trueValues;
if (inst.MatchIfInstruction(out condition, out trueInst) &&
AnalyzeCondition(condition, out trueValues)
)
{
trueValues = trueValues.IntersectWith(inputValues);
Block trueBlock;
if (trueInst.MatchBranch(out trueBlock) && AnalyzeBlock(trueBlock, trueValues))
{
// OK, true block was further analyzed.
InnerBlocks.Add(trueBlock);
}
else
{
// Create switch section for trueInst.
AddSection(trueValues, trueInst);
}
}
else if (inst.OpCode == OpCode.SwitchInstruction)
{
if (AnalyzeSwitch((SwitchInstruction)inst, inputValues, out trueValues))
{
ContainsILSwitch = true; // OK
}
else // switch analysis failed (e.g. switchVar mismatch)
{
return(false);
}
}
else // unknown inst
{
return(false);
}
var remainingValues = inputValues.ExceptWith(trueValues);
ILInstruction falseInst = block.Instructions.Last();
Block falseBlock;
if (falseInst.MatchBranch(out falseBlock) && AnalyzeBlock(falseBlock, remainingValues))
{
// OK, false block was further analyzed.
InnerBlocks.Add(falseBlock);
}
else
{
// Create switch section for falseInst.
AddSection(remainingValues, falseInst);
}
return(true);
}