static Leave CombineExits(Block block)
{
if (!(block.Instructions.SecondToLastOrDefault() is IfInstruction ifInst && block.Instructions.LastOrDefault() is Leave leaveElse))
{
return(null);
}
if (!ifInst.FalseInst.MatchNop())
{
return(null);
}
// try to unwrap true branch to single instruction:
var trueInstruction = Block.Unwrap(ifInst.TrueInst);
// if the true branch is a block with multiple instructions:
// try to apply the combine exits transform to the nested block
// and then continue on that transformed block.
// Example:
// if (cond) {
// if (cond2) {
// leave (value)
// }
// leave (value2)
// }
// leave (value3)
// =>
// leave (if (cond) value else if (cond2) value2 else value3)
if (trueInstruction is Block nestedBlock && nestedBlock.Instructions.Count == 2)
{
trueInstruction = CombineExits(nestedBlock);
}
if (!(trueInstruction is Leave leave))
{
return(null);
}
if (!(leave.IsLeavingFunction && leaveElse.IsLeavingFunction))
{
return(null);
}
if (leave.Value.MatchNop() || leaveElse.Value.MatchNop())
{
return(null);
}
// if (cond) {
// leave (value)
// }
// leave (elseValue)
// =>
// leave (if (cond) value else elseValue)
IfInstruction value = new IfInstruction(ifInst.Condition, leave.Value, leaveElse.Value);
value.AddILRange(ifInst);
Leave combinedLeave = new Leave(leave.TargetContainer, value);
combinedLeave.AddILRange(leaveElse);
combinedLeave.AddILRange(leave);
ifInst.ReplaceWith(combinedLeave);
block.Instructions.RemoveAt(combinedLeave.ChildIndex + 1);
return(combinedLeave);
}