/// <summary>
/// Advance the backward slicer (paroxically by moving backwards in the
/// RTL instruction stream).
/// </summary>
/// <returns>True if progress was made, false if there was no work left to do.</returns>
public bool Step()
{
// Try finding a state that isn't at the beginning of its basic block.
SliceState state;
for (; ;)
{
if (!worklist.GetWorkItem(out state))
{
return(false);
}
this.state = state;
if (!state.IsInBeginningOfBlock())
{
break;
}
DebugEx.Verbose(trace, "Reached beginning of block {0}", state.block.Address);
var preds = host.GetPredecessors(state.block);
if (preds.Count == 0)
{
DebugEx.Verbose(trace, " No predecessors found for block {0}", state.block.Address);
DebugEx.Verbose(trace, " index: {0} ({1})", this.JumpTableIndex, this.JumpTableIndexInterval);
DebugEx.Verbose(trace, " expr: {0}", this.JumpTableFormat);
return(true);
}
foreach (var pred in preds)
{
if (!visited.Contains(pred))
{
visited.Add(pred);
var stms = host.GetBlockInstructions(pred).ToArray();
//$TODO: the hack below works around the fact that some
// Code instructions don't exist in "raw" RTL. We are
// checking for a magic 1-length array of nulls as a
// sentinel.
if (stms.Length == 1 && stms[0] == null)
{
break;
}
SliceState pstate = state.CreateNew(pred, state.block.Address);
worklist.Add(pstate);
DebugEx.Verbose(trace, " Added block {0} to worklist", pred.Address);
}
}
}
if (state.Step())
{
worklist.Add(state);
return(true);
}
else
{
return(worklist.Count > 0);
}
}
/// <summary>
/// Start a slice by examining any variables in the indirect jump
/// <paramref name="indirectJump"/>, then start tracing instructions
/// backwards beginning at instruction <paramref name="iInstr"/> in <paramref name="block"/>.
/// </summary>
/// <remarks>
/// Any expressions discovered in this step become the "roots"
/// of the backward slice. These roots are kept in the `Live` collection.
/// </remarks>
/// <param name="block">Basic block of instructions.</param>
/// <param name="iInstr">Index into the instructions in <paramref name="block"/>.</param>
/// <param name="indirectJump">Expression containing the target of the indirect call or jump.</param>
/// <returns>If backward slicing should continue.</returns>
public bool Start(RtlBlock block, int iInstr, Expression indirectJump)
{
this.state = new SliceState(this, block, iInstr);
visited.Add(block);
if (state.Start(indirectJump))
{
worklist.Add(state);
return(true);
}
else
{
return(false);
}
}
public SliceState CreateNew(RtlBlock block, Address addrSucc)
{
var state = new SliceState(this.slicer, block, 0)
{
JumpTableFormat = this.JumpTableFormat,
JumpTableIndex = this.JumpTableIndex,
JumpTableIndexInterval = this.JumpTableIndexInterval,
Live = new Dictionary <Expression, BackwardSlicerContext>(this.Live, this.Live.Comparer),
ccNext = this.ccNext,
invertCondition = this.invertCondition,
addrSucc = addrSucc,
blockCount = blockCount + 1
};
state.iInstr = state.instrs.Length - 1;
return(state);
}