/// <summary>
/// Ensures that every write to a pinned local is followed by a branch instruction.
/// This ensures the 'pinning region' does not involve any half blocks, which makes it easier to extract.
/// </summary>
void SplitBlocksAtWritesToPinnedLocals(BlockContainer container)
{
for (int i = 0; i < container.Blocks.Count; i++)
{
var block = container.Blocks[i];
for (int j = 0; j < block.Instructions.Count - 1; j++)
{
var inst = block.Instructions[j];
if (inst.MatchStLoc(out ILVariable v, out var value) && v.Kind == VariableKind.PinnedLocal)
{
if (block.Instructions[j + 1].OpCode != OpCode.Branch)
{
// split block after j:
context.Step("Split block after pinned local write", inst);
var newBlock = new Block();
for (int k = j + 1; k < block.Instructions.Count; k++)
{
newBlock.Instructions.Add(block.Instructions[k]);
}
newBlock.AddILRange(newBlock.Instructions[0]);
block.Instructions.RemoveRange(j + 1, newBlock.Instructions.Count);
block.Instructions.Add(new Branch(newBlock));
container.Blocks.Insert(i + 1, newBlock);
}
// in case of re-pinning (e.g. C++/CLI assignment to pin_ptr variable),
// it's possible for the new value to be dependent on the old.
if (v.IsUsedWithin(value))
{
// In this case, we need to un-inline the uses of the pinned local
// so that they are split off into the block prior to the pinned local write
var temp = context.Function.RegisterVariable(VariableKind.StackSlot, v.Type);
block.Instructions.Insert(j++, new StLoc(temp, new LdLoc(v)));
foreach (var descendant in value.Descendants)
{
if (descendant.MatchLdLoc(v))
{
descendant.ReplaceWith(new LdLoc(temp).WithILRange(descendant));
}
}
}
if (j > 0)
{
// split block before j:
context.Step("Split block before pinned local write", inst);
var newBlock = new Block();
newBlock.Instructions.Add(block.Instructions[j]);
newBlock.Instructions.Add(block.Instructions[j + 1]);
newBlock.AddILRange(newBlock.Instructions[0]);
Debug.Assert(block.Instructions.Count == j + 2);
block.Instructions.RemoveRange(j, 2);
block.Instructions.Insert(j, new Branch(newBlock));
container.Blocks.Insert(i + 1, newBlock);
}
}
}
}
}
/// <summary>
/// Ensures that every write to a pinned local is followed by a branch instruction.
/// This ensures the 'pinning region' does not involve any half blocks, which makes it easier to extract.
/// </summary>
void SplitBlocksAtWritesToPinnedLocals(BlockContainer container)
{
for (int i = 0; i < container.Blocks.Count; i++)
{
var block = container.Blocks[i];
for (int j = 0; j < block.Instructions.Count - 1; j++)
{
var inst = block.Instructions[j];
ILVariable v;
if (inst.MatchStLoc(out v) && v.Kind == VariableKind.PinnedLocal)
{
if (block.Instructions[j + 1].OpCode != OpCode.Branch)
{
// split block after j:
context.Step("Split block after pinned local write", inst);
var newBlock = new Block();
for (int k = j + 1; k < block.Instructions.Count; k++)
{
newBlock.Instructions.Add(block.Instructions[k]);
}
newBlock.AddILRange(newBlock.Instructions[0]);
block.Instructions.RemoveRange(j + 1, newBlock.Instructions.Count);
block.Instructions.Add(new Branch(newBlock));
container.Blocks.Insert(i + 1, newBlock);
}
if (j > 0)
{
// split block before j:
context.Step("Split block before pinned local write", inst);
var newBlock = new Block();
newBlock.Instructions.Add(block.Instructions[j]);
newBlock.Instructions.Add(block.Instructions[j + 1]);
Debug.Assert(block.Instructions.Count == j + 2);
block.Instructions.RemoveRange(j, 2);
block.Instructions.Insert(j, new Branch(newBlock));
container.Blocks.Insert(i + 1, newBlock);
}
}
}
}
}
static bool CombineBlockWithNextBlock(BlockContainer container, Block block, ILTransformContext context)
{
Debug.Assert(container == block.Parent);
// Ensure the block will stay a basic block -- we don't want extended basic blocks prior to LoopDetection.
if (block.Instructions.Count > 1 && block.Instructions[block.Instructions.Count - 2].HasFlag(InstructionFlags.MayBranch))
{
return(false);
}
Branch br = block.Instructions.Last() as Branch;
// Check whether we can combine the target block with this block
if (br == null || br.TargetBlock.Parent != container || br.TargetBlock.IncomingEdgeCount != 1)
{
return(false);
}
if (br.TargetBlock == block)
{
return(false); // don't inline block into itself
}
context.Step("CombineBlockWithNextBlock", br);
var targetBlock = br.TargetBlock;
if (targetBlock.StartILOffset < block.StartILOffset && IsDeadTrueStore(block))
{
// The C# compiler generates a dead store for the condition of while (true) loops.
block.Instructions.RemoveRange(block.Instructions.Count - 3, 2);
}
if (block.ILRangeIsEmpty)
{
block.AddILRange(targetBlock);
}
block.Instructions.Remove(br);
block.Instructions.AddRange(targetBlock.Instructions);
targetBlock.Instructions.Clear(); // mark targetBlock for deletion
return(true);
}
bool MatchForLoop(BlockContainer loop, IfInstruction whileCondition, Block whileLoopBody)
{
// for loops have exactly two incoming edges at the entry point.
if (loop.EntryPoint.IncomingEdgeCount != 2)
{
return(false);
}
// try to find an increment block:
// consists of simple statements only.
var incrementBlock = GetIncrementBlock(loop, whileLoopBody);
if (incrementBlock != null)
{
// we found a possible increment block, just make sure, that there are at least three blocks:
// - condition block
// - loop body
// - increment block
if (incrementBlock.Instructions.Count <= 1 || loop.Blocks.Count < 3)
{
return(false);
}
context.Step("Transform to for loop", loop);
// move the block to the end of the loop:
loop.Blocks.MoveElementToEnd(incrementBlock);
loop.Kind = ContainerKind.For;
}
else
{
// we need to move the increment statements into its own block:
// last must be a branch entry-point
var last = whileLoopBody.Instructions.LastOrDefault();
var secondToLast = whileLoopBody.Instructions.SecondToLastOrDefault();
if (last == null || secondToLast == null)
{
return(false);
}
if (!last.MatchBranch(loop.EntryPoint))
{
return(false);
}
// we only deal with 'numeric' increments
if (!MatchIncrement(secondToLast, out var incrementVariable))
{
return(false);
}
// the increment variable must be local/stack variable
if (incrementVariable.Kind == VariableKind.Parameter)
{
return(false);
}
// split conditions:
var conditions = new List <ILInstruction>();
SplitConditions(whileCondition.Condition, conditions);
IfInstruction forCondition = null;
int numberOfConditions = 0;
foreach (var condition in conditions)
{
// the increment variable must be used in the condition
if (!condition.Descendants.Any(inst => inst.MatchLdLoc(incrementVariable)))
{
break;
}
// condition should not contain an assignment
if (condition.Descendants.Any(IsAssignment))
{
break;
}
if (forCondition == null)
{
forCondition = new IfInstruction(condition, whileCondition.TrueInst, whileCondition.FalseInst);
}
else
{
forCondition.Condition = IfInstruction.LogicAnd(forCondition.Condition, condition);
}
numberOfConditions++;
}
if (numberOfConditions == 0)
{
return(false);
}
context.Step("Transform to for loop", loop);
// split condition block:
whileCondition.ReplaceWith(forCondition);
ExpressionTransforms.RunOnSingleStatement(forCondition, context);
for (int i = conditions.Count - 1; i >= numberOfConditions; i--)
{
IfInstruction inst;
whileLoopBody.Instructions.Insert(0, inst = new IfInstruction(Comp.LogicNot(conditions[i]), new Leave(loop)));
ExpressionTransforms.RunOnSingleStatement(inst, context);
}
// create a new increment block and add it at the end:
int secondToLastIndex = secondToLast.ChildIndex;
var newIncremenBlock = new Block();
loop.Blocks.Add(newIncremenBlock);
// move the increment instruction:
newIncremenBlock.Instructions.Add(secondToLast);
newIncremenBlock.Instructions.Add(last);
newIncremenBlock.AddILRange(secondToLast.ILRange);
whileLoopBody.Instructions.RemoveRange(secondToLastIndex, 2);
whileLoopBody.Instructions.Add(new Branch(newIncremenBlock));
// complete transform.
loop.Kind = ContainerKind.For;
}
return(true);
}
private void DetectSwitchBody(Block block, SwitchInstruction switchInst)
{
Debug.Assert(block.Instructions.Last() == switchInst);
ControlFlowNode h = context.ControlFlowNode; // CFG node for our switch head
Debug.Assert(h.UserData == block);
Debug.Assert(!TreeTraversal.PreOrder(h, n => n.DominatorTreeChildren).Any(n => n.Visited));
isSwitch = true;
loopContext = new SwitchDetection.LoopContext(context.ControlFlowGraph, h);
var nodesInSwitch = new List <ControlFlowNode>();
nodesInSwitch.Add(h);
h.Visited = true;
ExtendLoop(h, nodesInSwitch, out var exitPoint);
if (exitPoint != null && h.Dominates(exitPoint) && exitPoint.Predecessors.Count == 1 && !HasReachableExit(exitPoint))
{
// If the exit point is reachable from just one single "break;",
// it's better to move the code into the switch.
// (unlike loops which should not be nested unless necessary,
// nesting switches makes it clearer in which cases a piece of code is reachable)
nodesInSwitch.AddRange(TreeTraversal.PreOrder(exitPoint, p => p.DominatorTreeChildren));
foreach (var node in nodesInSwitch)
{
node.Visited = true;
}
exitPoint = null;
}
context.Step("Create BlockContainer for switch", switchInst);
// Sort blocks in the loop in reverse post-order to make the output look a bit nicer.
// (if the loop doesn't contain nested loops, this is a topological sort)
nodesInSwitch.Sort((a, b) => b.PostOrderNumber.CompareTo(a.PostOrderNumber));
Debug.Assert(nodesInSwitch[0] == h);
foreach (var node in nodesInSwitch)
{
node.Visited = false; // reset visited flag so that we can find outer loops
Debug.Assert(h.Dominates(node), "The switch body must be dominated by the switch head");
}
BlockContainer switchContainer = new BlockContainer(ContainerKind.Switch);
Block newEntryPoint = new Block();
newEntryPoint.AddILRange(switchInst);
switchContainer.Blocks.Add(newEntryPoint);
newEntryPoint.Instructions.Add(switchInst);
block.Instructions[block.Instructions.Count - 1] = switchContainer;
Block exitTargetBlock = (Block)exitPoint?.UserData;
if (exitTargetBlock != null)
{
block.Instructions.Add(new Branch(exitTargetBlock));
}
switchContainer.AddILRange(newEntryPoint);
MoveBlocksIntoContainer(nodesInSwitch, switchContainer);
// Rewrite branches within the loop from oldEntryPoint to newEntryPoint:
foreach (var branch in switchContainer.Descendants.OfType <Branch>())
{
if (branch.TargetBlock == exitTargetBlock)
{
branch.ReplaceWith(new Leave(switchContainer).WithILRange(branch));
}
}
isSwitch = false;
}