/// <summary>Returns lattices for the start of all blocks reachable from the roots.
/// Note that this may return zero or negative length blocks.</summary>
public Dictionary <BasicBlock, LATTICE> Analyze(LatticeFunctions <LATTICE> functions, LATTICE initialState)
{
Dictionary <BasicBlock, LATTICE> inputStates;
if (m_workList.Count > 0)
{
Profile.Start("Dataflow Analyze");
inputStates = DoAnalyze(functions, initialState);
Profile.Stop("Dataflow Analyze");
}
else
{
inputStates = new Dictionary <BasicBlock, LATTICE>();
}
return(inputStates);
}
// This is a standard iterative data-flow analysis algorithm. See Advanced
// Compiler Design and Implementation by Muchnick for example.
private Dictionary <BasicBlock, LATTICE> DoAnalyze(LatticeFunctions <LATTICE> functions, LATTICE initialState)
{
// Remove the first block from the work list since we know it's value.
Unused.Value = m_workList.Remove(m_entry);
// Initialize the input states for all of the blocks. For the first
// block we are given the state. For the other blocks we use the
// top (zero) value.
var inputStates = new Dictionary <BasicBlock, LATTICE>();
inputStates.Add(m_entry, initialState);
foreach (BasicBlock block in m_workList)
{
inputStates.Add(block, functions.Top);
}
// Initialize the output states for all of the blocks.
var outputStates = new Dictionary <BasicBlock, LATTICE>();
outputStates.Add(m_entry, functions.Transform(initialState, m_entry));
foreach (BasicBlock block in m_workList)
{
outputStates.Add(block, functions.Top);
}
// While we have blocks to process,
while (m_workList.Count > 0)
{
// pop the first block,
BasicBlock block = m_workList[0];
m_workList.RemoveAt(0);
Log.DebugLine(this, "processing block {0:S}", block);
Log.Indent();
// and for every predecessor,
LATTICE totalEffect = functions.Top;
foreach (BasicBlock pred in m_predecessors[block])
{
// meet the current state of our block with the output state
// of the predecessor block,
totalEffect = functions.Meet(totalEffect, outputStates[pred]);
Log.DebugLine(this, "meeting {0:S}, out state: {1}", pred, outputStates[pred]);
Log.DebugLine(this, "meet state: {0}", totalEffect);
}
// and if the value changes queue it up again.
if (functions.DiffersFrom(totalEffect, inputStates[block]))
{
Log.DebugLine(this, "queuing up the block again");
inputStates[block] = totalEffect;
outputStates[block] = functions.Transform(totalEffect, block);
m_workList.Add(block);
}
Log.Unindent();
}
return(inputStates);
}
