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 = null;
if (!(loop.EntryPoint.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))
{
return(false);
}
context.Step("Transform to while (condition) loop", 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);
* }
* }*/
// Invert condition and unwrap nested block, if loop ends in a break or return statement preceeded by an IfInstruction.
/*while (loopBody.Instructions.Last() is Leave leave && loopBody.Instructions.SecondToLastOrDefault() is IfInstruction nestedIf && nestedIf.FalseInst.MatchNop()) {
* switch (nestedIf.TrueInst) {
* case Block nestedBlock:
* loopBody.Instructions.RemoveAt(leave.ChildIndex);
* loopBody.Instructions.AddRange(nestedBlock.Instructions);
* break;
* case Branch br:
* leave.ReplaceWith(nestedIf.TrueInst);
* break;
* default:
* return true;
* }
* nestedIf.Condition = Comp.LogicNot(nestedIf.Condition);
* nestedIf.TrueInst = leave;
* ExpressionTransforms.RunOnSingleStatment(nestedIf, context);
* if (!loopBody.HasFlag(InstructionFlags.EndPointUnreachable))
* loopBody.Instructions.Add(new Leave(loop));
* }*/
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);
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);
}
