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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using Internal.TypeSystem;
using Debug = System.Diagnostics.Debug;
namespace Internal.Runtime
{
/// <summary>
/// Utility class for encoding GCDescs. GCDesc is a runtime structure used by the
/// garbage collector that describes the GC layout of a memory region.
/// </summary>
public struct GCDescEncoder
{
/// <summary>
/// Retrieves size of the GCDesc that describes the instance GC layout for the given type.
/// </summary>
public static int GetGCDescSize(TypeDesc type)
{
if (type.IsArray)
{
TypeDesc elementType = ((ArrayType)type).ElementType;
if (elementType.IsGCPointer)
{
// For efficiency this is special cased and encoded as one serie.
return 3 * type.Context.Target.PointerSize;
}
else if (elementType.IsDefType)
{
var defType = (DefType)elementType;
if (defType.ContainsGCPointers)
{
GCPointerMap pointerMap = GCPointerMap.FromInstanceLayout(defType);
if (pointerMap.IsAllGCPointers)
{
// For efficiency this is special cased and encoded as one serie.
return 3 * type.Context.Target.PointerSize;
}
else
{
int numSeries = pointerMap.NumSeries;
Debug.Assert(numSeries > 0);
return (numSeries + 2) * type.Context.Target.PointerSize;
}
}
}
}
else
{
var defType = (DefType)type;
if (defType.ContainsGCPointers)
{
int numSeries = GCPointerMap.FromInstanceLayout(defType).NumSeries;
Debug.Assert(numSeries > 0);
return (numSeries * 2 + 1) * type.Context.Target.PointerSize;
}
}
return 0;
}
public static void EncodeGCDesc<T>(ref T builder, TypeDesc type)
where T : struct, ITargetBinaryWriter
{
int initialBuilderPosition = builder.CountBytes;
if (type.IsArray)
{
TypeDesc elementType = ((ArrayType)type).ElementType;
// 2 means m_pEEType and _numComponents. Syncblock is sort of appended at the end of the object layout in this case.
int baseSize = 2 * builder.TargetPointerSize;
if (type.IsMdArray)
{
// Multi-dim arrays include upper and lower bounds for each rank
baseSize += 2 * sizeof(int) * ((ArrayType)type).Rank;
}
if (elementType.IsGCPointer)
{
EncodeAllGCPointersArrayGCDesc(ref builder, baseSize);
}
else if (elementType.IsDefType)
{
var elementDefType = (DefType)elementType;
if (elementDefType.ContainsGCPointers)
{
GCPointerMap pointerMap = GCPointerMap.FromInstanceLayout(elementDefType);
if (pointerMap.IsAllGCPointers)
{
EncodeAllGCPointersArrayGCDesc(ref builder, baseSize);
}
else
{
EncodeArrayGCDesc(ref builder, pointerMap, baseSize);
}
}
}
}
else
{
var defType = (DefType)type;
if (defType.ContainsGCPointers)
{
// Computing the layout for the boxed version if this is a value type.
int offs = defType.IsValueType ? builder.TargetPointerSize : 0;
// Include syncblock
int objectSize = defType.InstanceByteCount.AsInt + offs + builder.TargetPointerSize;
EncodeStandardGCDesc(ref builder, GCPointerMap.FromInstanceLayout(defType), objectSize, offs);
}
}
Debug.Assert(initialBuilderPosition + GetGCDescSize(type) == builder.CountBytes);
}
public static void EncodeStandardGCDesc<T>(ref T builder, GCPointerMap map, int size, int delta)
where T : struct, ITargetBinaryWriter
{
Debug.Assert(size >= map.Size);
int pointerSize = builder.TargetPointerSize;
int numSeries = 0;
for (int cellIndex = map.Size - 1; cellIndex >= 0; cellIndex--)
{
if (map[cellIndex])
{
numSeries++;
int seriesSize = pointerSize;
while (cellIndex > 0 && map[cellIndex - 1])
{
seriesSize += pointerSize;
cellIndex--;
}
builder.EmitNaturalInt(seriesSize - size);
builder.EmitNaturalInt(cellIndex * pointerSize + delta);
}
}
Debug.Assert(numSeries > 0);
builder.EmitNaturalInt(numSeries);
}
// Arrays of all GC references are encoded as special kind of GC desc for efficiency
private static void EncodeAllGCPointersArrayGCDesc<T>(ref T builder, int baseSize)
where T : struct, ITargetBinaryWriter
{
// Construct the gc info as if this array contains exactly one pointer
// - the encoding trick where the size of the series is measured as a difference from
// total object size will make this work for arbitrary array lengths
// Series size
builder.EmitNaturalInt(-(baseSize + builder.TargetPointerSize));
// Series offset
builder.EmitNaturalInt(baseSize);
// NumSeries
builder.EmitNaturalInt(1);
}
private static void EncodeArrayGCDesc<T>(ref T builder, GCPointerMap map, int baseSize)
where T : struct, ITargetBinaryWriter
{
// NOTE: This format cannot properly represent element types with sizes >= 64k bytes.
// We guard it with an assert, but it is the responsibility of the code using this
// to cap array component sizes. MethodTable only has a UInt16 field for component sizes too.
int numSeries = 0;
int leadingNonPointerCount = 0;
int pointerSize = builder.TargetPointerSize;
for (int cellIndex = 0; cellIndex < map.Size && !map[cellIndex]; cellIndex++)
{
leadingNonPointerCount++;
}
int nonPointerCount = leadingNonPointerCount;
for (int cellIndex = map.Size - 1; cellIndex >= leadingNonPointerCount; cellIndex--)
{
if (map[cellIndex])
{
numSeries++;
int pointerCount = 1;
while (cellIndex > leadingNonPointerCount && map[cellIndex - 1])
{
cellIndex--;
pointerCount++;
}
Debug.Assert(pointerCount < 64 * 1024);
builder.EmitHalfNaturalInt((short)pointerCount);
Debug.Assert(nonPointerCount * pointerSize < 64 * 1024);
builder.EmitHalfNaturalInt((short)(nonPointerCount * pointerSize));
nonPointerCount = 0;
}
else
{
nonPointerCount++;
}
}
Debug.Assert(numSeries > 0);
builder.EmitNaturalInt(baseSize + leadingNonPointerCount * pointerSize);
builder.EmitNaturalInt(-numSeries);
}
}
}
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