Add support for array initialization based on RuntimeHelpers.CreateSpan<T>

Author: ds5678

ICSharpCode.Decompiler.Tests/TestCases/Pretty/InitializerTests.cs

@@ -805,6 +805,19 @@ private static void OutOfMemory()
 			array[0] = 1;
 			Console.WriteLine(array.Length);
 		}
+
+#if !NET40 && CS70
+		public static ReadOnlySpan<byte> ReadOnlySpanInitializer_ByteArray()
+		{
+			return new byte[3] { 1, 2, 3 };
+		}
+
+		public static ReadOnlySpan<int> ReadOnlySpanInitializer_Int32Array()
+		{
+			return new int[3] { 1, 2, 3 };
+		}
+#endif
+
 		#endregion
 
 		#region Object initializers

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -289,6 +289,12 @@ protected internal override void VisitCall(Call inst)
 				replacement.AcceptVisitor(this);
 				return;
 			}
+			if (TransformArrayInitializers.TransformRuntimeHelpersCreateSpanInitialization(inst, context, out var replacement2))
+			{
+				context.Step("TransformRuntimeHelpersCreateSpanInitialization: single-dim", inst);
+				inst.ReplaceWith(replacement2);
+				return;
+			}
 			base.VisitCall(inst);
 			TransformAssignment.HandleCompoundAssign(inst, context);
 		}

ICSharpCode.Decompiler/IL/Transforms/TransformArrayInitializers.cs

@@ -143,6 +143,40 @@ internal static bool TransformSpanTArrayInitialization(NewObj inst, StatementTra
 			return false;
 		}
 
+		internal static bool TransformRuntimeHelpersCreateSpanInitialization(Call inst, StatementTransformContext context, out ILInstruction replacement)
+		{
+			replacement = null;
+			if (!context.Settings.ArrayInitializers)
+				return false;
+			if (MatchRuntimeHelpersCreateSpan(inst, context, out var elementType, out var field))
+			{
+				if (field.HasFlag(System.Reflection.FieldAttributes.HasFieldRVA))
+				{
+					var valuesList = new List<ILInstruction>();
+					var initialValue = field.GetInitialValue(context.PEFile, context.TypeSystem);
+					var elementTypeSize = elementType.GetSize();
+					if (elementTypeSize <= 0 || initialValue.Length % elementTypeSize != 0)
+						return false;
+
+					var size = initialValue.Length / elementTypeSize;
+					if (context.Settings.Utf8StringLiterals &&
+						elementType.IsKnownType(KnownTypeCode.Byte) &&
+						DecodeUTF8String(initialValue, size, out string text))
+					{
+						replacement = new LdStrUtf8(text);
+						return true;
+					}
+					if (DecodeArrayInitializer(elementType, initialValue, new[] { size }, valuesList))
+					{
+						var tempStore = context.Function.RegisterVariable(VariableKind.InitializerTarget, new ArrayType(context.TypeSystem, elementType));
+						replacement = BlockFromInitializer(tempStore, elementType, new[] { size }, valuesList.ToArray());
+						return true;
+					}
+				}
+			}
+			return false;
+		}
+
 		private static unsafe bool DecodeUTF8String(BlobReader blob, int size, out string text)
 		{
 			if (size > blob.RemainingBytes)
@@ -187,6 +221,27 @@ static bool MatchSpanTCtorWithPointerAndSize(NewObj newObj, StatementTransformCo
 			return true;
 		}
 
+		static bool MatchRuntimeHelpersCreateSpan(Call inst, StatementTransformContext context, out IType elementType, out FieldDefinition field)
+		{
+			field = default;
+			elementType = null;
+			IType type = inst.Method.DeclaringType;
+			if (type.Namespace != "System.Runtime.CompilerServices" || type.Name != "RuntimeHelpers" || type.TypeParameterCount != 0)
+				return false;
+			if (inst.Arguments.Count != 1)
+				return false;
+			IMethod method = inst.Method;
+			if (method.Name != "CreateSpan" || method.TypeArguments.Count != 1)
+				return false;
+			elementType = method.TypeArguments[0];
+			if (!inst.Arguments[0].UnwrapConv(ConversionKind.StopGCTracking).MatchLdMemberToken(out var member))
+				return false;
+			if (member.MetadataToken.IsNil)
+				return false;
+			field = context.PEFile.Metadata.GetFieldDefinition((FieldDefinitionHandle)member.MetadataToken);
+			return true;
+		}
+
 		bool DoTransformMultiDim(ILFunction function, Block body, int pos)
 		{
 			if (pos >= body.Instructions.Count - 2)