* Optimize `TryAllocateRegWithtoutSpill` a bit * Add a fast path for when all registers are live. * Do not query `GetOverlapPosition` if the register is already in use (i.e: free position is 0). * Do not allocate child split list if not parent * Turn `LiveRange` into a reference struct `LiveRange` is now a reference wrapping struct like `Operand` and `Operation`. It has also been changed into a singly linked-list. In micro-benchmarks traversing the linked-list was faster than binary search on `List<T>`. Even for quite large input sizes (e.g: 1,000,000), surprisingly. Could be because the code gen for traversing the linked-list is much much cleaner and there is no virtual dispatch happening when checking if intervals overlaps. * Turn `LiveInterval` into an iterator The LSRA allocates in forward order and never inspect previous `LiveInterval` once they are expired. Something similar can be done for the `LiveRange`s within the `LiveInterval`s themselves. The `LiveInterval` is turned into a iterator which expires `LiveRange` within it. The iterator is moved forward along with interval walking code, i.e: AllocateInterval(context, interval, cIndex). * Remove `LinearScanAllocator.Sources` Local methods are less susceptible to do allocations than lambdas. * Optimize `GetOverlapPosition(interval)` a bit Time complexity should be in O(n+m) instead of O(nm) now. * Optimize `NumberLocals` a bit Use the same idea as in `HybridAllocator` to store the visited state in the MSB of the Operand's value instead of using a `HashSet<T>`. * Optimize `InsertSplitCopies` a bit Avoid allocating a redundant `CopyResolver`. * Optimize `InsertSplitCopiesAtEdges` a bit Avoid redundant allocations of `CopyResolver`. * Use stack allocation for `freePositions` Avoid redundant computations. * Add `UseList` Replace `SortedIntegerList` with an even more specialized data structure. It allocates memory on the arena allocators and does not require copying use positions when splitting it. * Turn `LiveInterval` into a reference struct `LiveInterval` is now a reference wrapping struct like `Operand` and `Operation`. The rationale behind turning this in a reference wrapping struct is because a `LiveInterval` is associated with each local variable, and these intervals may themselves be split further. I've seen translations having up to 8000 local variables. To make the `LiveInterval` unmanaged, a new data structure called `LiveIntervalList` was added to store child splits. This differs from `SortedList<,>` because it can contain intervals with the same start position. Really wished we got some more of C++ template in C#. :^( * Optimize `GetChildSplit` a bit No need to inspect the remaining ranges if we've reached a range which starts after position, since the split list is ordered. * Optimize `CopyResolver` a bit Lazily allocate the fill, spill and parallel copy structures since most of the time only one of them is needed. * Optimize `BitMap.Enumerator` a bit Marking `MoveNext` as `AggressiveInlining` allows RyuJIT to promote the `Enumerator` struct into registers completely, reducing load/store code a lot since it does not have to store the struct on the stack for ABI purposes. * Use stack allocation for `use/blockedPositions` * Optimize `AllocateWithSpill` a bit * Address feedback * Make `LiveInterval.AddRange(,)` more conservative Produces no diff against master, but just for good measure.