bool DoTransformStackAllocInitializer(Block body, int pos)
{
if (pos >= body.Instructions.Count - 2)
{
return(false);
}
ILInstruction inst = body.Instructions[pos];
if (inst.MatchStLoc(out var v, out var locallocExpr) && locallocExpr.MatchLocAlloc(out var lengthInst))
{
if (lengthInst.MatchLdcI(out var lengthInBytes) && HandleCpblkInitializer(body, pos + 1, v, lengthInBytes, out var blob, out var elementType))
{
context.Step("HandleCpblkInitializer", inst);
var block = new Block(BlockKind.StackAllocInitializer);
var tempStore = context.Function.RegisterVariable(VariableKind.InitializerTarget, new PointerType(elementType));
block.Instructions.Add(new StLoc(tempStore, locallocExpr));
while (blob.RemainingBytes > 0)
{
block.Instructions.Add(StElemPtr(tempStore, blob.Offset, new LdcI4(blob.ReadByte()), elementType));
}
block.FinalInstruction = new LdLoc(tempStore);
body.Instructions[pos] = new StLoc(v, block);
body.Instructions.RemoveAt(pos + 1);
ILInlining.InlineIfPossible(body, pos, context);
ExpressionTransforms.RunOnSingleStatement(body.Instructions[pos], context);
return(true);
}
if (HandleSequentialLocAllocInitializer(body, pos + 1, v, locallocExpr, out elementType, out StObj[] values, out int instructionsToRemove))
{
context.Step("HandleSequentialLocAllocInitializer", inst);
var block = new Block(BlockKind.StackAllocInitializer);
var tempStore = context.Function.RegisterVariable(VariableKind.InitializerTarget, new PointerType(elementType));
block.Instructions.Add(new StLoc(tempStore, locallocExpr));
block.Instructions.AddRange(values.Where(value => value != null).Select(value => RewrapStore(tempStore, value, elementType)));
block.FinalInstruction = new LdLoc(tempStore);
body.Instructions[pos] = new StLoc(v, block);
body.Instructions.RemoveRange(pos + 1, instructionsToRemove);
ILInlining.InlineIfPossible(body, pos, context);
ExpressionTransforms.RunOnSingleStatement(body.Instructions[pos], context);
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.EntryPoint.Label, 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.EntryPoint.Label, 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);
whileLoopBody.Instructions.RemoveRange(secondToLastIndex, 2);
whileLoopBody.Instructions.Add(new Branch(newIncremenBlock));
// complete transform.
loop.Kind = ContainerKind.For;
}
return(true);
}
bool MatchWhileLoop(BlockContainer loop, out IfInstruction condition, out Block loopBody)
{
// ConditionDetection favours leave inside if and branch at end of block
// while-loop:
// if (!loop-condition) leave loop-container
// ...
condition = null;
loopBody = loop.EntryPoint;
if (!(loopBody.Instructions[0] is IfInstruction ifInstruction))
{
return(false);
}
if (!ifInstruction.FalseInst.MatchNop())
{
return(false);
}
if (UsesVariableCapturedInLoop(loop, ifInstruction.Condition))
{
return(false);
}
condition = ifInstruction;
if (!ifInstruction.TrueInst.MatchLeave(loop))
{
// sometimes the loop-body is nested within the if
// if (loop-condition) { loop-body }
// leave loop-container
if (loopBody.Instructions.Count != 2 || !loop.EntryPoint.Instructions.Last().MatchLeave(loop))
{
return(false);
}
if (!ifInstruction.TrueInst.HasFlag(InstructionFlags.EndPointUnreachable))
{
((Block)ifInstruction.TrueInst).Instructions.Add(new Leave(loop));
}
ConditionDetection.InvertIf(loopBody, ifInstruction, context);
}
context.Step("Transform to while (condition) loop: " + loop.EntryPoint.Label, loop);
loop.Kind = ContainerKind.While;
//invert comparison
ifInstruction.Condition = Comp.LogicNot(ifInstruction.Condition);
ifInstruction.FalseInst = ifInstruction.TrueInst;
//move the rest of the body into a new block
loopBody = ConditionDetection.ExtractBlock(loop.EntryPoint, 1, loop.EntryPoint.Instructions.Count);
loop.Blocks.Insert(1, loopBody);
if (!loopBody.HasFlag(InstructionFlags.EndPointUnreachable))
{
loopBody.Instructions.Add(new Leave(loop));
}
ifInstruction.TrueInst = new Branch(loopBody);
ExpressionTransforms.RunOnSingleStatement(ifInstruction, context);
// Analyze conditions and decide whether to move some of them out of the condition block:
/*var conditions = new List<ILInstruction>();
* SplitConditions(condition.Condition, conditions);
* // Break apart conditions that could be a MoveNext call followed by a Current accessor call:
* if (MightBeHeaderOfForEach(loop, conditions)) {
* ifInstruction.Condition = conditions[0];
* foreach (var cond in conditions.Skip(1).Reverse()) {
* IfInstruction inst;
* loopBody.Instructions.Insert(0, inst = new IfInstruction(Comp.LogicNot(cond), new Leave(loop)));
* ExpressionTransforms.RunOnSingleStatment(inst, context);
* }
* }*/
return(true);
}
/// <summary>
/// Matches a do-while loop and performs the following transformations:
/// - combine all compatible conditions into one IfInstruction.
/// - extract conditions into a condition block, or move the existing condition block to the end.
/// </summary>
bool MatchDoWhileLoop(BlockContainer loop)
{
(List <IfInstruction> conditions, ILInstruction exit, bool swap, bool split, bool unwrap) = AnalyzeDoWhileConditions(loop);
// not a do-while loop, exit.
if (conditions == null || conditions.Count == 0)
{
return(false);
}
context.Step("Transform to do-while loop: " + loop.EntryPoint.Label, loop);
Block conditionBlock;
// first we remove all extracted instructions from the original block.
var originalBlock = (Block)exit.Parent;
if (unwrap)
{
// we found a condition block nested in a condition that is followed by a return statement:
// we flip the condition and swap the blocks
Debug.Assert(originalBlock.Parent is IfInstruction);
var returnCondition = (IfInstruction)originalBlock.Parent;
var topLevelBlock = (Block)returnCondition.Parent;
Debug.Assert(topLevelBlock.Parent == loop);
var leaveFunction = topLevelBlock.Instructions[returnCondition.ChildIndex + 1];
Debug.Assert(leaveFunction.MatchReturn(out _));
returnCondition.Condition = Comp.LogicNot(returnCondition.Condition);
returnCondition.TrueInst = leaveFunction;
// simplify the condition:
ExpressionTransforms.RunOnSingleStatement(returnCondition, context);
topLevelBlock.Instructions.RemoveAt(returnCondition.ChildIndex + 1);
topLevelBlock.Instructions.AddRange(originalBlock.Instructions);
originalBlock = topLevelBlock;
split = true;
}
originalBlock.Instructions.RemoveRange(originalBlock.Instructions.Count - conditions.Count - 1, conditions.Count + 1);
// we need to split the block:
if (split)
{
// add a new block at the end and add a branch to the new block.
conditionBlock = new Block();
loop.Blocks.Add(conditionBlock);
originalBlock.Instructions.Add(new Branch(conditionBlock));
}
else
{
// move the condition block to the end.
conditionBlock = originalBlock;
loop.Blocks.MoveElementToEnd(originalBlock);
}
// combine all conditions and the exit instruction into one IfInstruction:
IfInstruction condition = null;
conditionBlock.AddILRange(exit);
foreach (var inst in conditions)
{
conditionBlock.AddILRange(inst);
if (condition == null)
{
condition = inst;
if (swap)
{
// branches must be swapped and condition negated:
condition.Condition = Comp.LogicNot(condition.Condition);
condition.FalseInst = condition.TrueInst;
condition.TrueInst = exit;
}
else
{
condition.FalseInst = exit;
}
}
else
{
if (swap)
{
condition.Condition = IfInstruction.LogicAnd(Comp.LogicNot(inst.Condition), condition.Condition);
}
else
{
condition.Condition = IfInstruction.LogicAnd(inst.Condition, condition.Condition);
}
}
}
// insert the combined conditions into the condition block:
conditionBlock.Instructions.Add(condition);
// simplify the condition:
ExpressionTransforms.RunOnSingleStatement(condition, context);
// transform complete
loop.Kind = ContainerKind.DoWhile;
return(true);
}
