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JIT: Coalesce copies on LSRA with simple register preferencing (#6950)

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* JIT: Coalesce copies on LSRA with simple register preferencing

* PPTC version bump
This commit is contained in:
gdkchan 2024-06-19 09:39:29 -03:00 • committed by GitHub
parent d25a084858
commit 0afa8f2c14
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3 changed files with 56 additions and 6 deletions
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39
src/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
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@ -251,7 +251,20 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
}
}
int selectedReg = GetHighestValueIndex(freePositions);
// If this is a copy destination variable, we prefer the register used for the copy source.
// If the register is available, then the copy can be eliminated later as both source
// and destination will use the same register.
int selectedReg;
if (current.TryGetCopySourceRegister(out int preferredReg) && freePositions[preferredReg] >= current.GetEnd())
{
selectedReg = preferredReg;
}
else
{
selectedReg = GetHighestValueIndex(freePositions);
}
int selectedNextUse = freePositions[selectedReg];
// Intervals starts and ends at odd positions, unless they span an entire
@ -431,7 +444,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
}
}
private static int GetHighestValueIndex(Span<int> span)
private static int GetHighestValueIndex(ReadOnlySpan<int> span)
{
int highest = int.MinValue;
@ -798,12 +811,12 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
// The "visited" state is stored in the MSB of the local's value.
const ulong VisitedMask = 1ul << 63;
bool IsVisited(Operand local)
static bool IsVisited(Operand local)
{
return (local.GetValueUnsafe() & VisitedMask) != 0;
}
void SetVisited(Operand local)
static void SetVisited(Operand local)
{
local.GetValueUnsafe() |= VisitedMask;
}
@ -826,9 +839,25 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
{
dest.NumberLocal(_intervals.Count);
_intervals.Add(new LiveInterval(dest));
LiveInterval interval = new LiveInterval(dest);
_intervals.Add(interval);
SetVisited(dest);
// If this is a copy (or copy-like operation), set the copy source interval as well.
// This is used for register preferencing later on, which allows the copy to be eliminated
// in some cases.
if (node.Instruction == Instruction.Copy || node.Instruction == Instruction.ZeroExtend32)
{
Operand source = node.GetSource(0);
if (source.Kind == OperandKind.LocalVariable &&
source.GetLocalNumber() > 0 &&
(node.Instruction == Instruction.Copy || source.Type == OperandType.I32))
{
interval.SetCopySource(_intervals[source.GetLocalNumber()]);
}
}
}
}
}