Add transformation for stackalloc to Span<T>.

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -287,6 +287,12 @@ namespace ICSharpCode.Decompiler.CSharp
 
 		protected internal override TranslatedExpression VisitNewObj(NewObj inst, TranslationContext context)
 		{
+			var type = inst.Method.DeclaringType;
+			if (type.IsKnownType(KnownTypeCode.SpanOfT) || type.IsKnownType(KnownTypeCode.ReadOnlySpanOfT)) {
+				if (inst.Arguments.Count == 2 && inst.Arguments[0] is Block b && b.Kind == BlockKind.StackAllocInitializer) {
+					return TranslateStackAllocInitializer(b, type.TypeArguments[0]);
+				}
+			}
 			return new CallBuilder(this, typeSystem, settings).Build(inst);
 		}
 		
@@ -310,6 +316,24 @@ namespace ICSharpCode.Decompiler.CSharp
 				.WithILInstruction(inst).WithRR(new ResolveResult(new PointerType(elementType)));
 		}
 
+		protected internal override TranslatedExpression VisitLocAllocSpan(LocAllocSpan inst, TranslationContext context)
+		{
+			return TranslateLocAllocSpan(inst, context.TypeHint, out var elementType)
+				.WithILInstruction(inst).WithRR(new ResolveResult(inst.Type));
+		}
+
+		StackAllocExpression TranslateLocAllocSpan(LocAllocSpan inst, IType typeHint, out IType elementType)
+		{
+			elementType = inst.Type.TypeArguments[0];
+			PointerType pointerType = new PointerType(elementType);
+			TranslatedExpression countExpression = Translate(inst.Argument)
+				.ConvertTo(compilation.FindType(KnownTypeCode.Int32), this);
+			return new StackAllocExpression {
+				Type = ConvertType(elementType),
+				CountExpression = countExpression
+			};
+		}
+
 		StackAllocExpression TranslateLocAlloc(LocAlloc inst, IType typeHint, out IType elementType)
 		{
 			TranslatedExpression countExpression;
@@ -2258,13 +2282,20 @@ namespace ICSharpCode.Decompiler.CSharp
 			var final = block.FinalInstruction as LdLoc;
 			if (stloc == null || final == null || stloc.Variable != final.Variable || stloc.Variable.Kind != VariableKind.InitializerTarget)
 				throw new ArgumentException("given Block is invalid!");
-			if (!(stloc.Value is LocAlloc locAlloc))
-				throw new ArgumentException("given Block is invalid!");
-
-			var stackAllocExpression = TranslateLocAlloc(locAlloc, typeHint, out var elementType);
+			StackAllocExpression stackAllocExpression;
+			IType elementType;
+			switch (stloc.Value) {
+				case LocAlloc locAlloc:
+					stackAllocExpression = TranslateLocAlloc(locAlloc, typeHint, out elementType);
+					break;
+				case LocAllocSpan locAllocSpan:
+					stackAllocExpression = TranslateLocAllocSpan(locAllocSpan, typeHint, out elementType);
+					break;
+				default:
+					throw new ArgumentException("given Block is invalid!");
+			}
 			var initializer = stackAllocExpression.Initializer = new ArrayInitializerExpression();
 			var pointerType = new PointerType(elementType);
-
 			long expectedOffset = 0;
 
 			for (int i = 1; i < block.Instructions.Count; i++) {
@@ -2272,10 +2303,13 @@ namespace ICSharpCode.Decompiler.CSharp
 				if (!block.Instructions[i].MatchStObj(out var target, out var value, out var t) || !TypeUtils.IsCompatibleTypeForMemoryAccess(elementType, t))
 					throw new ArgumentException("given Block is invalid!");
 				long offset = 0;
+				target = target.UnwrapConv(ConversionKind.StopGCTracking);
+
 				if (!target.MatchLdLoc(stloc.Variable)) {
 					if (!target.MatchBinaryNumericInstruction(BinaryNumericOperator.Add, out var left, out var right))
 						throw new ArgumentException("given Block is invalid!");
 					var binary = (BinaryNumericInstruction)target;
+					left = left.UnwrapConv(ConversionKind.StopGCTracking);
 					var offsetInst = PointerArithmeticOffset.Detect(right, pointerType, binary.CheckForOverflow);
 					if (!left.MatchLdLoc(final.Variable) || offsetInst == null)
 						throw new ArgumentException("given Block is invalid!");

ICSharpCode.Decompiler/CSharp/Transforms/IntroduceUnsafeModifier.cs

@@ -142,7 +142,7 @@ namespace ICSharpCode.Decompiler.CSharp.Transforms
 		public override bool VisitStackAllocExpression(StackAllocExpression stackAllocExpression)
 		{
 			base.VisitStackAllocExpression(stackAllocExpression);
-			return true;
+			return stackAllocExpression.GetResolveResult().Type is PointerType;
 		}
 		
 		public override bool VisitInvocationExpression(InvocationExpression invocationExpression)

ICSharpCode.Decompiler/IL/Instructions.cs

@@ -141,6 +141,8 @@ namespace ICSharpCode.Decompiler.IL
 		LdMemberToken,
 		/// <summary>Allocates space in the stack frame</summary>
 		LocAlloc,
+		/// <summary>Allocates space in the stack frame and wraps it in a Span</summary>
+		LocAllocSpan,
 		/// <summary>memcpy(destAddress, sourceAddress, size);</summary>
 		Cpblk,
 		/// <summary>memset(address, value, size)</summary>
@@ -3192,6 +3194,60 @@ namespace ICSharpCode.Decompiler.IL
 	}
 }
 namespace ICSharpCode.Decompiler.IL
+{
+	/// <summary>Allocates space in the stack frame and wraps it in a Span</summary>
+	public sealed partial class LocAllocSpan : UnaryInstruction
+	{
+		public LocAllocSpan(ILInstruction argument, IType type) : base(OpCode.LocAllocSpan, argument)
+		{
+			this.type = type;
+		}
+		IType type;
+		/// <summary>Returns the type operand.</summary>
+		public IType Type {
+			get { return type; }
+			set { type = value; InvalidateFlags(); }
+		}
+		public override StackType ResultType { get { return StackType.O; } }
+		protected override InstructionFlags ComputeFlags()
+		{
+			return base.ComputeFlags() | InstructionFlags.MayThrow;
+		}
+		public override InstructionFlags DirectFlags {
+			get {
+				return base.DirectFlags | InstructionFlags.MayThrow;
+			}
+		}
+		public override void WriteTo(ITextOutput output, ILAstWritingOptions options)
+		{
+			ILRange.WriteTo(output, options);
+			output.Write(OpCode);
+			output.Write(' ');
+			type.WriteTo(output);
+			output.Write('(');
+			Argument.WriteTo(output, options);
+			output.Write(')');
+		}
+		public override void AcceptVisitor(ILVisitor visitor)
+		{
+			visitor.VisitLocAllocSpan(this);
+		}
+		public override T AcceptVisitor<T>(ILVisitor<T> visitor)
+		{
+			return visitor.VisitLocAllocSpan(this);
+		}
+		public override T AcceptVisitor<C, T>(ILVisitor<C, T> visitor, C context)
+		{
+			return visitor.VisitLocAllocSpan(this, context);
+		}
+		protected internal override bool PerformMatch(ILInstruction other, ref Patterns.Match match)
+		{
+			var o = other as LocAllocSpan;
+			return o != null && this.Argument.PerformMatch(o.Argument, ref match) && type.Equals(o.type);
+		}
+	}
+}
+namespace ICSharpCode.Decompiler.IL
 {
 	/// <summary>memcpy(destAddress, sourceAddress, size);</summary>
 	public sealed partial class Cpblk : ILInstruction, ISupportsVolatilePrefix, ISupportsUnalignedPrefix
@@ -6497,6 +6553,10 @@ namespace ICSharpCode.Decompiler.IL
 		{
 			Default(inst);
 		}
+		protected internal virtual void VisitLocAllocSpan(LocAllocSpan inst)
+		{
+			Default(inst);
+		}
 		protected internal virtual void VisitCpblk(Cpblk inst)
 		{
 			Default(inst);
@@ -6875,6 +6935,10 @@ namespace ICSharpCode.Decompiler.IL
 		{
 			return Default(inst);
 		}
+		protected internal virtual T VisitLocAllocSpan(LocAllocSpan inst)
+		{
+			return Default(inst);
+		}
 		protected internal virtual T VisitCpblk(Cpblk inst)
 		{
 			return Default(inst);
@@ -7253,6 +7317,10 @@ namespace ICSharpCode.Decompiler.IL
 		{
 			return Default(inst, context);
 		}
+		protected internal virtual T VisitLocAllocSpan(LocAllocSpan inst, C context)
+		{
+			return Default(inst, context);
+		}
 		protected internal virtual T VisitCpblk(Cpblk inst, C context)
 		{
 			return Default(inst, context);
@@ -7470,6 +7538,7 @@ namespace ICSharpCode.Decompiler.IL
 			"ldtypetoken",
 			"ldmembertoken",
 			"localloc",
+			"localloc.span",
 			"cpblk",
 			"initblk",
 			"ldflda",
@@ -7816,6 +7885,18 @@ namespace ICSharpCode.Decompiler.IL
 			argument = default(ILInstruction);
 			return false;
 		}
+		public bool MatchLocAllocSpan(out ILInstruction argument, out IType type)
+		{
+			var inst = this as LocAllocSpan;
+			if (inst != null) {
+				argument = inst.Argument;
+				type = inst.Type;
+				return true;
+			}
+			argument = default(ILInstruction);
+			type = default(IType);
+			return false;
+		}
 		public bool MatchCpblk(out ILInstruction destAddress, out ILInstruction sourceAddress, out ILInstruction size)
 		{
 			var inst = this as Cpblk;

ICSharpCode.Decompiler/IL/Instructions.tt

@@ -218,6 +218,8 @@
 			CustomClassName("LdMemberToken"), NoArguments, HasMemberOperand, ResultType("O")),
 		new OpCode("localloc", "Allocates space in the stack frame",
 			CustomClassName("LocAlloc"), Unary, ResultType("I"), MayThrow),
+		new OpCode("localloc.span", "Allocates space in the stack frame and wraps it in a Span",
+			CustomClassName("LocAllocSpan"), Unary, HasTypeOperand, ResultType("O"), MayThrow),
 		new OpCode("cpblk", "memcpy(destAddress, sourceAddress, size);",
 			CustomArguments(("destAddress", new[] { "I", "Ref" }), ("sourceAddress", new[] { "I", "Ref" }), ("size", new[] { "I4" })),
 			MayThrow, MemoryAccess,

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -262,15 +262,82 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 		protected internal override void VisitNewObj(NewObj inst)
 		{
-			LdcDecimal decimalConstant;
-			if (TransformDecimalCtorToConstant(inst, out decimalConstant)) {
+			if (TransformDecimalCtorToConstant(inst, out LdcDecimal decimalConstant)) {
 				context.Step("TransformDecimalCtorToConstant", inst);
 				inst.ReplaceWith(decimalConstant);
 				return;
 			}
+			if (TransformSpanTCtorContainingStackAlloc(inst, out ILInstruction locallocSpan)) {
+				inst.ReplaceWith(locallocSpan);
+				Block block = null;
+				ILInstruction stmt = locallocSpan;
+				while (stmt.Parent != null) {
+					if (stmt.Parent is Block b) {
+						block = b;
+						break;
+					}
+					stmt = stmt.Parent;
+				}
+				//ILInlining.InlineIfPossible(block, stmt.ChildIndex - 1, context);
+				return;
+			}
 			base.VisitNewObj(inst);
 		}
-		
+
+		/// <summary>
+		/// newobj Span..ctor(localloc(conv i4->u &lt;zero extend&gt;(ldc.i4 sizeInBytes)), numberOfElementsExpr)
+		/// =>
+		/// localloc.span T(numberOfElementsExpr)
+		/// 
+		/// -or-
+		/// 
+		/// newobj Span..ctor(Block IL_0000 (StackAllocInitializer) {
+		///		stloc I_0(localloc(conv i4->u&lt;zero extend>(ldc.i4 sizeInBytes)))
+		///		...
+		///		final: ldloc I_0
+		///	}, numberOfElementsExpr)
+		/// =>
+		/// Block IL_0000 (StackAllocInitializer) {
+		///		stloc I_0(localloc.span T(numberOfElementsExpr))
+		///		...
+		///		final: ldloc I_0
+		/// }
+		/// </summary>
+		bool TransformSpanTCtorContainingStackAlloc(NewObj newObj, out ILInstruction locallocSpan)
+		{
+			locallocSpan = null;
+			IType type = newObj.Method.DeclaringType;
+			if (!type.IsKnownType(KnownTypeCode.SpanOfT) && !type.IsKnownType(KnownTypeCode.ReadOnlySpanOfT))
+				return false;
+			if (newObj.Arguments.Count != 2 || type.TypeArguments.Count != 1)
+				return false;
+			if (newObj.Arguments[0] is LocAlloc) {
+				locallocSpan = new LocAllocSpan(newObj.Arguments[1], type);
+				return true;
+			}
+			if (newObj.Arguments[0] is Block initializer && initializer.Kind == BlockKind.StackAllocInitializer) {
+				if (!initializer.Instructions[0].MatchStLoc(out var initializerVariable, out var value))
+					return false;
+				if (!value.MatchLocAlloc(out _))
+					return false;
+				var newVariable = initializerVariable.Function.RegisterVariable(VariableKind.InitializerTarget, type);
+				foreach (var load in initializerVariable.LoadInstructions.ToArray()) {
+					ILInstruction newInst = new LdLoc(newVariable);
+					newInst.AddILRange(load.ILRange);
+					if (load.Parent != initializer)
+						newInst = new Conv(newInst, PrimitiveType.I, false, Sign.None);
+					load.ReplaceWith(newInst);
+				}
+				foreach (var store in initializerVariable.StoreInstructions.ToArray()) {
+					store.Variable = newVariable;
+				}
+				value.ReplaceWith(new LocAllocSpan(newObj.Arguments[1], type));
+				locallocSpan = initializer;
+				return true;
+			}
+			return false;
+		}
+
 		bool TransformDecimalCtorToConstant(NewObj inst, out LdcDecimal result)
 		{
 			IType t = inst.Method.DeclaringType;

ICSharpCode.Decompiler/IL/Transforms/ILInlining.cs

@@ -359,6 +359,8 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					if (parent.Parent.OpCode == OpCode.DynamicCompoundAssign)
 						return true; // inline into dynamic compound assignments
 					break;
+				case OpCode.LocAllocSpan:
+					return true; // inline size-expressions into localloc.span
 			}
 			// decide based on the target into which we are inlining
 			switch (next.OpCode) {

ICSharpCode.Decompiler/IL/Transforms/TransformArrayInitializers.cs

@@ -128,7 +128,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					context.Step("HandleCpblkInitializer", inst);
 					var block = new Block(BlockKind.StackAllocInitializer);
 					var tempStore = context.Function.RegisterVariable(VariableKind.InitializerTarget, new PointerType(elementType));
-					block.Instructions.Add(new StLoc(tempStore, new LocAlloc(lengthInst)));
+					block.Instructions.Add(new StLoc(tempStore, locallocExpr));
 
 					while (blob.RemainingBytes > 0) {
 						block.Instructions.Add(StElemPtr(tempStore, blob.Offset, new LdcI4(blob.ReadByte()), elementType));
@@ -138,18 +138,20 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					body.Instructions[pos] = new StLoc(v, block);
 					body.Instructions.RemoveAt(pos + 1);
 					ILInlining.InlineIfPossible(body, pos, context);
+					ExpressionTransforms.RunOnSingleStatement(body.Instructions[pos], context);
 					return true;
 				}
-				if (HandleSequentialLocAllocInitializer(body, pos + 1, v, lengthInst, out elementType, out StObj[] values, out int instructionsToRemove)) {
+				if (HandleSequentialLocAllocInitializer(body, pos + 1, v, locallocExpr, out elementType, out StObj[] values, out int instructionsToRemove)) {
 					context.Step("HandleSequentialLocAllocInitializer", inst);
 					var block = new Block(BlockKind.StackAllocInitializer);
 					var tempStore = context.Function.RegisterVariable(VariableKind.InitializerTarget, new PointerType(elementType));
-					block.Instructions.Add(new StLoc(tempStore, new LocAlloc(lengthInst)));
+					block.Instructions.Add(new StLoc(tempStore, locallocExpr));
 					block.Instructions.AddRange(values.Where(value => value != null).Select(value => RewrapStore(tempStore, value, elementType)));
 					block.FinalInstruction = new LdLoc(tempStore);
 					body.Instructions[pos] = new StLoc(v, block);
 					body.Instructions.RemoveRange(pos + 1, instructionsToRemove);
 					ILInlining.InlineIfPossible(body, pos, context);
+					ExpressionTransforms.RunOnSingleStatement(body.Instructions[pos], context);
 					return true;
 				}
 			}
@@ -178,7 +180,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			return true;
 		}
 
-		bool HandleSequentialLocAllocInitializer(Block block, int pos, ILVariable store, ILInstruction lengthInstruction, out IType elementType, out StObj[] values, out int instructionsToRemove)
+		bool HandleSequentialLocAllocInitializer(Block block, int pos, ILVariable store, ILInstruction locAllocInstruction, out IType elementType, out StObj[] values, out int instructionsToRemove)
 		{
 			int elementCount = 0;
 			long minExpectedOffset = 0;
@@ -186,10 +188,13 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			elementType = null;
 			instructionsToRemove = 0;
 
+			if (!locAllocInstruction.MatchLocAlloc(out var lengthInstruction))
+				return false;
+
 			if (block.Instructions[pos].MatchInitblk(out var dest, out var value, out var size)
 				&& lengthInstruction.MatchLdcI(out long byteCount))
 			{
-				if (!dest.MatchLdLoc(store) || !value.MatchLdcI4(0) || !size.MatchLdcI(byteCount))
+				if (!dest.MatchLdLoc(store) || !size.MatchLdcI(byteCount))
 					return false;
 				instructionsToRemove++;
 				pos++;