/// <summary>
/// Computes the liveness for the given register
/// </summary>
/// <param name="backflowGraph">The backflow graph</param>
/// <param name="register">The register</param>
/// <param name="useSites">The use sites</param>
/// <param name="aliveAt">The instructions which the register is alive</param>
private static void ComputeLiveness(BackflowGraph backflowGraph, VirtualRegister register, IList<UsageSite> useSites, ISet<int> aliveAt)
{
foreach (var useSite in useSites)
{
ComputeLiveness(
backflowGraph,
useSite.Block,
useSite.Offset,
new HashSet<VirtualBasicBlock>(),
register,
aliveAt);
}
}
/// <summary>
/// Computes the liveness for the given register
/// </summary>
/// <param name="backflowGraph">The backflow graph</param>
/// <param name="basicBlock">The current block</param>
/// <param name="startOffset">The offset in the current block</param>
/// <param name="visited">The visited blocks</param>
/// <param name="register">The current register</param>
/// <param name="aliveAt">The instructions which the register is alive</param>
private static void ComputeLiveness(
BackflowGraph backflowGraph,
VirtualBasicBlock basicBlock, int startOffset,
ISet<VirtualBasicBlock> visited,
VirtualRegister register, ISet<int> aliveAt)
{
if (visited.Contains(basicBlock))
{
return;
}
visited.Add(basicBlock);
bool terminated = false;
for (int i = startOffset; i >= 0; i--)
{
var instruction = basicBlock.Instructions[i];
if (instruction.AssignRegister == register)
{
if (!instruction.UsesRegisters.Contains(register))
{
aliveAt.Add(i + basicBlock.StartOffset);
terminated = true;
break;
}
}
aliveAt.Add(i + basicBlock.StartOffset);
}
//If we have not terminated the search, search edges flowing backwards from the current block
if (!terminated)
{
ISet<VirtualBasicBlock> edges;
if (backflowGraph.Edges.TryGetValue(basicBlock, out edges))
{
foreach (var backEdge in edges)
{
ComputeLiveness(
backflowGraph,
backEdge,
backEdge.Instructions.Count - 1,
visited,
register,
aliveAt);
}
}
}
}
