Ryujinx/ARMeilleure/CodeGen/RegisterAllocators/UseList.cs
FICTURE7 69093cf2d6
Optimize LSRA (#2563)
* 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.
2021-10-08 18:15:44 -03:00

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2.2 KiB
C#

using System;
namespace ARMeilleure.CodeGen.RegisterAllocators
{
unsafe struct UseList
{
private int* _items;
private int _capacity;
private int _count;
public int Count => _count;
public int FirstUse => _count > 0 ? _items[_count - 1] : LiveInterval.NotFound;
public Span<int> Span => new(_items, _count);
public void Add(int position)
{
if (_count + 1 > _capacity)
{
var oldSpan = Span;
_capacity = Math.Max(4, _capacity * 2);
_items = Allocators.Default.Allocate<int>((uint)_capacity);
var newSpan = Span;
oldSpan.CopyTo(newSpan);
}
// Use positions are usually inserted in descending order, so inserting in descending order is faster,
// since the number of half exchanges is reduced.
int i = _count - 1;
while (i >= 0 && _items[i] < position)
{
_items[i + 1] = _items[i--];
}
_items[i + 1] = position;
_count++;
}
public int NextUse(int position)
{
int index = NextUseIndex(position);
return index != LiveInterval.NotFound ? _items[index] : LiveInterval.NotFound;
}
public int NextUseIndex(int position)
{
int i = _count - 1;
if (i == -1 || position > _items[0])
{
return LiveInterval.NotFound;
}
while (i >= 0 && _items[i] < position)
{
i--;
}
return i;
}
public UseList Split(int position)
{
int index = NextUseIndex(position);
// Since the list is in descending order, the new split list takes the front of the list and the current
// list takes the back of the list.
UseList result = new();
result._count = index + 1;
result._capacity = result._count;
result._items = _items;
_count = _count - result._count;
_capacity = _count;
_items = _items + result._count;
return result;
}
}
}