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ILSpy/ICSharpCode.Decompiler/IL/ControlFlow/DetectPinnedRegions.cs

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// Copyright (c) 2016 Daniel Grunwald
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using ICSharpCode.Decompiler.IL.Transforms;
using ICSharpCode.Decompiler.TypeSystem;
namespace ICSharpCode.Decompiler.IL.ControlFlow
{
/// <summary>
/// IL uses 'pinned locals' to prevent the GC from moving objects.
///
/// C#:
/// <code>
/// fixed (int* s = &amp;arr[index]) { use(s); use(s); }
/// </code>
///
/// <para>Gets translated into IL:</para>
/// <code>
/// pinned local P : System.Int32&amp;
///
/// stloc(P, ldelema(arr, index))
/// call use(conv ref->i(ldloc P))
/// call use(conv ref->i(ldloc P))
/// stloc(P, conv i4->u(ldc.i4 0))
/// </code>
///
/// In C#, the only way to pin something is to use a fixed block
/// (or to mess around with GCHandles).
/// But fixed blocks are scoped, so we need to detect the region affected by the pin.
/// To ensure we'll be able to collect all blocks in that region, we perform this transform
/// early, before building any other control flow constructs that aren't as critical for correctness.
///
/// This means this transform must run before LoopDetection.
/// To make our detection job easier, we must run after variable inlining.
/// </summary>
public class DetectPinnedRegions : IILTransform
{
ILTransformContext context;
public void Run(ILFunction function, ILTransformContext context)
{
this.context = context;
foreach (var container in function.Descendants.OfType<BlockContainer>()) {
context.CancellationToken.ThrowIfCancellationRequested();
DetectNullSafeArrayToPointer(container);
SplitBlocksAtWritesToPinnedLocals(container);
foreach (var block in container.Blocks)
CreatePinnedRegion(block);
container.Blocks.RemoveAll(b => b.Instructions.Count == 0); // remove dummy blocks
}
// Sometimes there's leftover writes to the original pinned locals
foreach (var block in function.Descendants.OfType<Block>()) {
context.CancellationToken.ThrowIfCancellationRequested();
for (int i = 0; i < block.Instructions.Count; i++) {
var stloc = block.Instructions[i] as StLoc;
if (stloc != null && stloc.Variable.Kind == VariableKind.PinnedLocal && stloc.Variable.LoadCount == 0 && stloc.Variable.AddressCount == 0) {
if (SemanticHelper.IsPure(stloc.Value.Flags)) {
block.Instructions.RemoveAt(i--);
} else {
stloc.ReplaceWith(stloc.Value);
}
}
}
}
this.context = null;
}
/// <summary>
/// Ensures that every write to a pinned local is followed by a branch instruction.
/// This ensures the 'pinning region' does not involve any half blocks, which makes it easier to extract.
/// </summary>
void SplitBlocksAtWritesToPinnedLocals(BlockContainer container)
{
for (int i = 0; i < container.Blocks.Count; i++) {
var block = container.Blocks[i];
for (int j = 0; j < block.Instructions.Count - 1; j++) {
var inst = block.Instructions[j];
ILVariable v;
if (inst.MatchStLoc(out v) && v.Kind == VariableKind.PinnedLocal && block.Instructions[j + 1].OpCode != OpCode.Branch) {
// split block after j:
context.Step("Split block after pinned local write", inst);
var newBlock = new Block();
for (int k = j + 1; k < block.Instructions.Count; k++) {
newBlock.Instructions.Add(block.Instructions[k]);
}
newBlock.ILRange = newBlock.Instructions[0].ILRange;
block.Instructions.RemoveRange(j + 1, newBlock.Instructions.Count);
block.Instructions.Add(new Branch(newBlock));
container.Blocks.Insert(i + 1, newBlock);
}
}
}
}
#region null-safe array to pointer
void DetectNullSafeArrayToPointer(BlockContainer container)
{
// Detect the following pattern:
// ...
// stloc V(ldloc S)
// if (comp(ldloc S == ldnull)) br B_null_or_empty
// br B_not_null
// }
// Block B_not_null {
// if (conv i->i4 (ldlen(ldloc V))) br B_not_null_and_not_empty
// br B_null_or_empty
// }
// Block B_not_null_and_not_empty {
// stloc P(ldelema(ldloc V, ldc.i4 0, ...))
// br B_target
// }
// Block B_null_or_empty {
// stloc P(conv i4->u(ldc.i4 0))
// br B_target
// }
// And convert the whole thing into:
// ...
// stloc P(array.to.pointer(V))
// br B_target
bool modified = false;
for (int i = 0; i < container.Blocks.Count; i++) {
var block = container.Blocks[i];
ILVariable v, p;
Block targetBlock;
if (IsNullSafeArrayToPointerPattern(block, out v, out p, out targetBlock)) {
context.Step("NullSafeArrayToPointerPattern", block);
ILInstruction arrayToPointer = new ArrayToPointer(new LdLoc(v));
if (p.StackType != StackType.Ref) {
arrayToPointer = new Conv(arrayToPointer, p.StackType.ToPrimitiveType(), false, Sign.None);
}
block.Instructions[block.Instructions.Count - 2] = new StLoc(p, arrayToPointer);
((Branch)block.Instructions.Last()).TargetBlock = targetBlock;
modified = true;
}
}
if (modified) {
container.Blocks.RemoveAll(b => b.IncomingEdgeCount == 0); // remove blocks made unreachable
}
}
bool IsNullSafeArrayToPointerPattern(Block block, out ILVariable v, out ILVariable p, out Block targetBlock)
{
v = null;
p = null;
targetBlock = null;
// ...
// if (comp(ldloc V == ldnull)) br B_null_or_empty
// br B_not_null
var ifInst = block.Instructions.SecondToLastOrDefault() as IfInstruction;
if (ifInst == null)
return false;
var condition = ifInst.Condition as Comp;
if (!(condition != null && condition.Kind == ComparisonKind.Equality && condition.Left.MatchLdLoc(out v) && condition.Right.MatchLdNull()))
return false;
bool usingPreviousVar = false;
if (v.Kind == VariableKind.StackSlot) {
// If the variable is a stack slot, that might be due to an inline assignment,
// so check the previous instruction:
var previous = block.Instructions.ElementAtOrDefault(block.Instructions.Count - 3) as StLoc;
if (previous != null && previous.Value.MatchLdLoc(v)) {
// stloc V(ldloc S)
// if (comp(ldloc S == ldnull)) ...
v = previous.Variable;
usingPreviousVar = true;
}
}
if (!ifInst.TrueInst.MatchBranch(out Block nullOrEmptyBlock))
return false;
if (!ifInst.FalseInst.MatchNop())
return false;
if (nullOrEmptyBlock.Parent != block.Parent)
return false;
if (!IsNullSafeArrayToPointerNullOrEmptyBlock(nullOrEmptyBlock, out p, out targetBlock))
return false;
if (!(p.Kind == VariableKind.PinnedLocal || (usingPreviousVar && v.Kind == VariableKind.PinnedLocal)))
return false;
if (!block.Instructions.Last().MatchBranch(out Block notNullBlock))
return false;
if (notNullBlock.Parent != block.Parent)
return false;
return IsNullSafeArrayToPointerNotNullBlock(notNullBlock, v, p, nullOrEmptyBlock, targetBlock);
}
bool IsNullSafeArrayToPointerNotNullBlock(Block block, ILVariable v, ILVariable p, Block nullOrEmptyBlock, Block targetBlock)
{
// Block B_not_null {
// if (conv i->i4 (ldlen(ldloc V))) br B_not_null_and_not_empty
// br B_null_or_empty
// }
if (block.Instructions.Count != 2)
return false;
if (!block.Instructions[0].MatchIfInstruction(out ILInstruction condition, out ILInstruction trueInst))
return false;
if (!condition.UnwrapConv(ConversionKind.Truncate).MatchLdLen(StackType.I, out ILInstruction array))
return false;
if (!array.MatchLdLoc(v))
return false;
if (!trueInst.MatchBranch(out Block notNullAndNotEmptyBlock))
return false;
if (notNullAndNotEmptyBlock.Parent != block.Parent)
return false;
if (!IsNullSafeArrayToPointerNotNullAndNotEmptyBlock(notNullAndNotEmptyBlock, v, p, targetBlock))
return false;
return block.Instructions[1].MatchBranch(nullOrEmptyBlock);
}
bool IsNullSafeArrayToPointerNotNullAndNotEmptyBlock(Block block, ILVariable v, ILVariable p, Block targetBlock)
{
// Block B_not_null_and_not_empty {
// stloc P(ldelema(ldloc V, ldc.i4 0, ...))
// br B_target
// }
ILInstruction value;
if (block.Instructions.Count != 2)
return false;
if (!block.Instructions[0].MatchStLoc(p, out value))
return false;
if (v.Kind == VariableKind.PinnedLocal) {
value = value.UnwrapConv(ConversionKind.StopGCTracking);
}
if (!(value is LdElema ldelema))
return false;
if (!ldelema.Array.MatchLdLoc(v))
return false;
if (!ldelema.Indices.All(i => i.MatchLdcI4(0)))
return false;
return block.Instructions[1].MatchBranch(targetBlock);
}
bool IsNullSafeArrayToPointerNullOrEmptyBlock(Block block, out ILVariable p, out Block targetBlock)
{
p = null;
targetBlock = null;
// Block B_null_or_empty {
// stloc P(conv i4->u(ldc.i4 0))
// br B_target
// }
ILInstruction value;
return block.Instructions.Count == 2
&& block.Instructions[0].MatchStLoc(out p, out value)
&& (p.Kind == VariableKind.PinnedLocal || p.Kind == VariableKind.Local)
&& IsNullOrZero(value)
&& block.Instructions[1].MatchBranch(out targetBlock);
}
#endregion
#region CreatePinnedRegion
bool CreatePinnedRegion(Block block)
{
// After SplitBlocksAtWritesToPinnedLocals(), only the second-to-last instruction in each block
// can be a write to a pinned local.
var stLoc = block.Instructions.SecondToLastOrDefault() as StLoc;
if (stLoc == null || stLoc.Variable.Kind != VariableKind.PinnedLocal)
return false;
// stLoc is a store to a pinned local.
if (IsNullOrZero(stLoc.Value))
return false; // ignore unpin instructions
// stLoc is a store that starts a new pinned region
// Collect the blocks to be moved into the region:
BlockContainer sourceContainer = (BlockContainer)block.Parent;
int[] reachedEdgesPerBlock = new int[sourceContainer.Blocks.Count];
Queue<Block> workList = new Queue<Block>();
Block entryBlock = ((Branch)block.Instructions.Last()).TargetBlock;
if (entryBlock.Parent != sourceContainer) {
// we didn't find a single block to be added to the pinned region
return false;
}
reachedEdgesPerBlock[entryBlock.ChildIndex]++;
workList.Enqueue(entryBlock);
while (workList.Count > 0) {
Block workItem = workList.Dequeue();
StLoc workStLoc = workItem.Instructions.SecondToLastOrDefault() as StLoc;
int instructionCount;
if (workStLoc != null && workStLoc.Variable == stLoc.Variable && IsNullOrZero(workStLoc.Value)) {
// found unpin instruction: only consider branches prior to that instruction
instructionCount = workStLoc.ChildIndex;
} else {
instructionCount = workItem.Instructions.Count;
}
for (int i = 0; i < instructionCount; i++) {
foreach (var branch in workItem.Instructions[i].Descendants.OfType<Branch>()) {
if (branch.TargetBlock.Parent == sourceContainer) {
if (branch.TargetBlock == block) {
// pin instruction is within a loop, and can loop around without an unpin instruction
// This should never happen for C#-compiled code, but may happen with C++/CLI code.
return false;
}
if (reachedEdgesPerBlock[branch.TargetBlock.ChildIndex]++ == 0) {
// detected first edge to that block: add block as work item
workList.Enqueue(branch.TargetBlock);
}
}
}
}
}
// Validate that all uses of a block consistently are inside or outside the pinned region.
// (we cannot do this anymore after we start moving blocks around)
for (int i = 0; i < sourceContainer.Blocks.Count; i++) {
if (reachedEdgesPerBlock[i] != 0 && reachedEdgesPerBlock[i] != sourceContainer.Blocks[i].IncomingEdgeCount) {
return false;
}
}
context.Step("CreatePinnedRegion", block);
BlockContainer body = new BlockContainer();
for (int i = 0; i < sourceContainer.Blocks.Count; i++) {
if (reachedEdgesPerBlock[i] > 0) {
var innerBlock = sourceContainer.Blocks[i];
Branch br = innerBlock.Instructions.LastOrDefault() as Branch;
if (br != null && br.TargetContainer == sourceContainer && reachedEdgesPerBlock[br.TargetBlock.ChildIndex] == 0) {
// branch that leaves body.
// Should have an instruction that resets the pin; delete that instruction:
StLoc innerStLoc = innerBlock.Instructions.SecondToLastOrDefault() as StLoc;
if (innerStLoc != null && innerStLoc.Variable == stLoc.Variable && IsNullOrZero(innerStLoc.Value)) {
innerBlock.Instructions.RemoveAt(innerBlock.Instructions.Count - 2);
}
}
body.Blocks.Add(innerBlock); // move block into body
sourceContainer.Blocks[i] = new Block(); // replace with dummy block
// we'll delete the dummy block later
}
}
stLoc.ReplaceWith(new PinnedRegion(stLoc.Variable, stLoc.Value, body));
block.Instructions.RemoveAt(block.Instructions.Count - 1); // remove branch into body
ProcessPinnedRegion((PinnedRegion)block.Instructions.Last());
return true;
}
static bool IsNullOrZero(ILInstruction inst)
{
while (inst is Conv conv) {
inst = conv.Argument;
}
return inst.MatchLdcI4(0) || inst.MatchLdNull();
}
#endregion
#region ProcessPinnedRegion
/// <summary>
/// After a pinned region was detected; process its body; replacing the pin variable
/// with a native pointer as far as possible.
/// </summary>
void ProcessPinnedRegion(PinnedRegion pinnedRegion)
{
if (pinnedRegion.Variable.Type.Kind == TypeKind.ByReference) {
// C# doesn't support a "by reference" variable, so replace it with a native pointer
context.Step("Replace pinned ref-local with native pointer", pinnedRegion);
ILVariable oldVar = pinnedRegion.Variable;
IType elementType = ((ByReferenceType)oldVar.Type).ElementType;
if (elementType.Kind == TypeKind.Pointer && pinnedRegion.Init.MatchLdFlda(out _, out var field)
&& ((PointerType)elementType).ElementType.Equals(field.Type))
{
// Roslyn 2.6 (C# 7.2) uses type "int*&" for the pinned local referring to a
// fixed field of type "int".
// Remove the extra level of indirection.
elementType = ((PointerType)elementType).ElementType;
}
ILVariable newVar = new ILVariable(
VariableKind.PinnedLocal,
new PointerType(elementType),
oldVar.Index);
newVar.Name = oldVar.Name;
newVar.HasGeneratedName = oldVar.HasGeneratedName;
oldVar.Function.Variables.Add(newVar);
ReplacePinnedVar(oldVar, newVar, pinnedRegion);
UseExistingVariableForPinnedRegion(pinnedRegion);
} else if (pinnedRegion.Variable.Type.Kind == TypeKind.Array) {
context.Step("Replace pinned array with native pointer", pinnedRegion);
MoveArrayToPointerToPinnedRegionInit(pinnedRegion);
UseExistingVariableForPinnedRegion(pinnedRegion);
} else if (pinnedRegion.Variable.Type.IsKnownType(KnownTypeCode.String)) {
// fixing a string
HandleStringToPointer(pinnedRegion);
}
// Detect nested pinned regions:
BlockContainer body = (BlockContainer)pinnedRegion.Body;
foreach (var block in body.Blocks)
CreatePinnedRegion(block);
body.Blocks.RemoveAll(b => b.Instructions.Count == 0); // remove dummy blocks
}
private void MoveArrayToPointerToPinnedRegionInit(PinnedRegion pinnedRegion)
{
// Roslyn started marking the array variable as pinned,
// and then uses array.to.pointer immediately within the region.
Debug.Assert(pinnedRegion.Variable.Type.Kind == TypeKind.Array);
if (pinnedRegion.Variable.StoreInstructions.Count != 1 || pinnedRegion.Variable.AddressCount != 0 || pinnedRegion.Variable.LoadCount != 1)
return;
var ldloc = pinnedRegion.Variable.LoadInstructions.Single();
if (!(ldloc.Parent is ArrayToPointer arrayToPointer))
return;
if (!(arrayToPointer.Parent is Conv conv && conv.Kind == ConversionKind.StopGCTracking))
return;
Debug.Assert(arrayToPointer.IsDescendantOf(pinnedRegion));
ILVariable oldVar = pinnedRegion.Variable;
ILVariable newVar = new ILVariable(
VariableKind.PinnedLocal,
new PointerType(((ArrayType)oldVar.Type).ElementType),
oldVar.Index);
newVar.Name = oldVar.Name;
newVar.HasGeneratedName = oldVar.HasGeneratedName;
oldVar.Function.Variables.Add(newVar);
pinnedRegion.Variable = newVar;
pinnedRegion.Init = new ArrayToPointer(pinnedRegion.Init) { ILRange = arrayToPointer.ILRange };
conv.ReplaceWith(new LdLoc(newVar) { ILRange = conv.ILRange });
}
void ReplacePinnedVar(ILVariable oldVar, ILVariable newVar, ILInstruction inst)
{
Debug.Assert(newVar.StackType == StackType.I);
if (inst is Conv conv && conv.Kind == ConversionKind.StopGCTracking && conv.Argument.MatchLdLoc(oldVar) && conv.ResultType == newVar.StackType) {
// conv ref->i (ldloc oldVar)
// => ldloc newVar
conv.AddILRange(conv.Argument.ILRange);
conv.ReplaceWith(new LdLoc(newVar) { ILRange = conv.ILRange });
return;
}
if (inst is IInstructionWithVariableOperand iwvo && iwvo.Variable == oldVar) {
iwvo.Variable = newVar;
if (inst is StLoc stloc && oldVar.Type.Kind == TypeKind.ByReference) {
stloc.Value = new Conv(stloc.Value, PrimitiveType.I, false, Sign.None);
}
if ((inst is LdLoc || inst is StLoc) && !IsSlotAcceptingBothManagedAndUnmanagedPointers(inst.SlotInfo) && oldVar.StackType != StackType.I) {
// wrap inst in Conv, so that the stack types match up
var children = inst.Parent.Children;
children[inst.ChildIndex] = new Conv(inst, oldVar.StackType.ToPrimitiveType(), false, Sign.None);
}
} else if (inst.MatchLdStr(out var val) && val == "Is this ILSpy?") {
inst.ReplaceWith(new LdStr("This is ILSpy!")); // easter egg ;)
return;
}
foreach (var child in inst.Children) {
ReplacePinnedVar(oldVar, newVar, child);
}
}
private bool IsSlotAcceptingBothManagedAndUnmanagedPointers(SlotInfo slotInfo)
{
return slotInfo == Block.InstructionSlot || slotInfo == LdObj.TargetSlot || slotInfo == StObj.TargetSlot;
}
bool IsBranchOnNull(ILInstruction condBranch, ILVariable nativeVar, out Block targetBlock)
{
targetBlock = null;
// if (comp(ldloc nativeVar == conv i4->i <sign extend>(ldc.i4 0))) br targetBlock
ILInstruction condition, trueInst, left, right;
return condBranch.MatchIfInstruction(out condition, out trueInst)
&& condition.MatchCompEquals(out left, out right)
&& left.MatchLdLoc(nativeVar) && IsNullOrZero(right)
&& trueInst.MatchBranch(out targetBlock);
}
void HandleStringToPointer(PinnedRegion pinnedRegion)
{
Debug.Assert(pinnedRegion.Variable.Type.IsKnownType(KnownTypeCode.String));
BlockContainer body = (BlockContainer)pinnedRegion.Body;
if (body.EntryPoint.IncomingEdgeCount != 1)
return;
// stloc nativeVar(conv o->i (ldloc pinnedVar))
// if (comp(ldloc nativeVar == conv i4->i <sign extend>(ldc.i4 0))) br targetBlock
// br adjustOffsetToStringData
if (!body.EntryPoint.Instructions[0].MatchStLoc(out ILVariable nativeVar, out ILInstruction initInst))
return;
ILVariable newVar;
if (body.EntryPoint.Instructions.Count != 3) {
// potentially a special case with legacy csc and an unused pinned variable:
if (nativeVar.IsSingleDefinition && nativeVar.LoadCount == 0 && initInst.MatchLdLoc(pinnedRegion.Variable)
&& pinnedRegion.Variable.LoadCount == 1)
{
// initInst is dead store
body.EntryPoint.Instructions.RemoveAt(0);
var charPtr = new PointerType(context.TypeSystem.FindType(KnownTypeCode.Char));
newVar = new ILVariable(VariableKind.PinnedLocal, charPtr, pinnedRegion.Variable.Index);
newVar.Name = pinnedRegion.Variable.Name;
newVar.HasGeneratedName = pinnedRegion.Variable.HasGeneratedName;
nativeVar.Function.Variables.Add(newVar);
pinnedRegion.Variable = newVar;
pinnedRegion.Init = new ArrayToPointer(pinnedRegion.Init);
}
return;
}
if (nativeVar.Type.GetStackType() != StackType.I)
return;
if (!initInst.UnwrapConv(ConversionKind.StopGCTracking).MatchLdLoc(pinnedRegion.Variable))
return;
if (!IsBranchOnNull(body.EntryPoint.Instructions[1], nativeVar, out Block targetBlock))
return;
if (targetBlock.Parent != body)
return;
if (!body.EntryPoint.Instructions[2].MatchBranch(out Block adjustOffsetToStringData))
return;
if (!(adjustOffsetToStringData.Parent == body && adjustOffsetToStringData.IncomingEdgeCount == 1
&& IsOffsetToStringDataBlock(adjustOffsetToStringData, nativeVar, targetBlock)))
return;
context.Step("Handle pinned string (with adjustOffsetToStringData)", pinnedRegion);
// remove old entry point
body.Blocks.RemoveAt(0);
body.Blocks.RemoveAt(adjustOffsetToStringData.ChildIndex);
// make targetBlock the new entry point
body.Blocks.RemoveAt(targetBlock.ChildIndex);
body.Blocks.Insert(0, targetBlock);
pinnedRegion.Init = new ArrayToPointer(pinnedRegion.Init);
ILVariable otherVar;
ILInstruction otherVarInit;
// In optimized builds, the 'nativeVar' may end up being a stack slot,
// and only gets assigned to a real variable after the offset adjustment.
if (nativeVar.Kind == VariableKind.StackSlot && nativeVar.LoadCount == 1
&& body.EntryPoint.Instructions[0].MatchStLoc(out otherVar, out otherVarInit)
&& otherVarInit.MatchLdLoc(nativeVar)
&& otherVar.IsSingleDefinition) {
body.EntryPoint.Instructions.RemoveAt(0);
nativeVar = otherVar;
}
if (nativeVar.Kind == VariableKind.Local) {
newVar = new ILVariable(VariableKind.PinnedLocal, nativeVar.Type, nativeVar.Index);
newVar.Name = nativeVar.Name;
newVar.HasGeneratedName = nativeVar.HasGeneratedName;
nativeVar.Function.Variables.Add(newVar);
ReplacePinnedVar(nativeVar, newVar, pinnedRegion);
} else {
newVar = nativeVar;
}
ReplacePinnedVar(pinnedRegion.Variable, newVar, pinnedRegion);
}
bool IsOffsetToStringDataBlock(Block block, ILVariable nativeVar, Block targetBlock)
{
// stloc nativeVar(add(ldloc nativeVar, conv i4->i <sign extend>(call [Accessor System.Runtime.CompilerServices.RuntimeHelpers.get_OffsetToStringData():System.Int32]())))
// br IL_0011
if (block.Instructions.Count != 2)
return false;
ILInstruction value;
if (nativeVar.IsSingleDefinition && nativeVar.LoadCount == 2) {
// If there are no loads (except for the two in the string-to-pointer pattern),
// then we might have split nativeVar:
if (!block.Instructions[0].MatchStLoc(out var otherVar, out value))
return false;
if (!(otherVar.IsSingleDefinition && otherVar.LoadCount == 0))
return false;
} else if (nativeVar.StoreCount == 2) {
// normal case with non-split variable
if (!block.Instructions[0].MatchStLoc(nativeVar, out value))
return false;
} else {
return false;
}
if (!value.MatchBinaryNumericInstruction(BinaryNumericOperator.Add, out ILInstruction left, out ILInstruction right))
return false;
if (!left.MatchLdLoc(nativeVar))
return false;
if (!IsOffsetToStringDataCall(right))
return false;
return block.Instructions[1].MatchBranch(targetBlock);
}
bool IsOffsetToStringDataCall(ILInstruction inst)
{
Call call = inst.UnwrapConv(ConversionKind.SignExtend) as Call;
return call != null && call.Method.FullName == "System.Runtime.CompilerServices.RuntimeHelpers.get_OffsetToStringData";
}
/// <summary>
/// Modifies a pinned region to eliminate an extra local variable that roslyn tends to generate.
/// </summary>
void UseExistingVariableForPinnedRegion(PinnedRegion pinnedRegion)
{
// PinnedRegion V_1(..., BlockContainer {
// Block IL_0000(incoming: 1) {
// stloc V_0(ldloc V_1)
// ...
if (!(pinnedRegion.Body is BlockContainer body))
return;
if (pinnedRegion.Variable.LoadCount != 1)
return;
if (!body.EntryPoint.Instructions[0].MatchStLoc(out var v, out var init))
return;
if (!init.MatchLdLoc(pinnedRegion.Variable))
return;
if (!(v.IsSingleDefinition && v.Type.Equals(pinnedRegion.Variable.Type)))
return;
if (v.Kind != VariableKind.Local)
return;
// replace V_1 with V_0
v.Kind = VariableKind.PinnedLocal;
pinnedRegion.Variable = v;
body.EntryPoint.Instructions.RemoveAt(0);
}
#endregion
}
}