Fix #2103: Support for `Stackalloc initializers` not working for `byte`

ICSharpCode.Decompiler.Tests/TestCases/Pretty/CS73_StackAllocInitializers.cs

@@ -396,6 +396,36 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return UseSpan(span);
 		}
 
+		public void Issue2103a()
+		{
+			Span<byte> span = stackalloc byte[3] {
+				1,
+				2,
+				3
+			};
+			Console.WriteLine(span[2] + span[0]);
+		}
+
+		public void Issue2103b()
+		{
+			Span<byte> span = stackalloc byte[3];
+			Console.WriteLine(span[0] + span[1]);
+		}
+
+		public void Issue2103c()
+		{
+			Console.WriteLine((stackalloc byte[3] {
+				1,
+				2,
+				3
+			})[2]);
+		}
+
+		public void Issue2103d()
+		{
+			Console.WriteLine((stackalloc byte[3])[1]);
+		}
+
 		public string UseSpan(Span<int> span)
 		{
 			throw new NotImplementedException();

ICSharpCode.Decompiler/CSharp/OutputVisitor/InsertParenthesesVisitor.cs

@@ -189,10 +189,15 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public override void VisitIndexerExpression(IndexerExpression indexerExpression)
 		{
 			ParenthesizeIfRequired(indexerExpression.Target, PrecedenceLevel.Primary);
-			ArrayCreateExpression ace = indexerExpression.Target as ArrayCreateExpression;
-			if (ace != null && (InsertParenthesesForReadability || ace.Initializer.IsNull)) {
-				// require parentheses for "(new int[1])[0]"
-				Parenthesize(indexerExpression.Target);
+			switch (indexerExpression.Target) {
+				case ArrayCreateExpression ace when InsertParenthesesForReadability || ace.Initializer.IsNull:
+					// require parentheses for "(new int[1])[0]"
+					Parenthesize(indexerExpression.Target);
+					break;
+				case StackAllocExpression sae when InsertParenthesesForReadability || sae.Initializer.IsNull:
+					// require parentheses for "(stackalloc int[1])[0]"
+					Parenthesize(indexerExpression.Target);
+					break;
 			}
 			base.VisitIndexerExpression(indexerExpression);
 		}

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -408,7 +408,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			var pointerType = new PointerType(elementType);
 			var elementCountInstr = PointerArithmeticOffset.Detect(sizeInBytesInstr, pointerType.ElementType, checkForOverflow: true, unwrapZeroExtension: true);
-			if (elementCountInstr == null || !elementCountInstr.Match(elementCountInstr2).Success)
+			if (elementCountInstr == null || !elementCountInstr.UnwrapConv(ConversionKind.ZeroExtend).Match(elementCountInstr2).Success)
 				return false;
 			return true;
 		}

ICSharpCode.Decompiler/IL/Transforms/TransformArrayInitializers.cs

@@ -227,17 +227,34 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				return false;
 			if (!dest.MatchLdLoc(v) || !src.MatchLdsFlda(out var field) || !size.MatchLdcI4((int)length))
 				return false;
-			if (field.MetadataToken.IsNil)
-				return false;
-			if (!block.Instructions[pos + 1].MatchStLoc(out var finalStore, out var value))
+			if (!(v.IsSingleDefinition && v.LoadCount == 2))
 				return false;
-			if (!value.MatchLdLoc(v))
+			if (field.MetadataToken.IsNil)
 				return false;
+			if (!block.Instructions[pos + 1].MatchStLoc(out var finalStore, out var value)) {
+				var otherLoadOfV = v.LoadInstructions.FirstOrDefault(l => !(l.Parent is Cpblk));
+				if (otherLoadOfV == null)
+					return false;
+				finalStore = otherLoadOfV.Parent.Extract();
+				value = ((StLoc)finalStore.StoreInstructions[0]).Value;
+				if (finalStore == null)
+					return false;
+			}
 			var fd = context.PEFile.Metadata.GetFieldDefinition((FieldDefinitionHandle)field.MetadataToken);
 			if (!fd.HasFlag(System.Reflection.FieldAttributes.HasFieldRVA))
 				return false;
+			if (value.MatchLdLoc(v)) {
+				elementType = ((PointerType)finalStore.Type).ElementType;
+			} else if (value is NewObj { Arguments: { Count: 2 } } newObj
+					&& newObj.Method.DeclaringType.IsKnownType(KnownTypeCode.SpanOfT)
+					&& newObj.Arguments[0].MatchLdLoc(v)
+					&& newObj.Arguments[1].MatchLdcI4((int)length))
+			{
+				elementType = ((ParameterizedType)newObj.Method.DeclaringType).TypeArguments[0];
+			} else {
+				return false;
+			}
 			blob = fd.GetInitialValue(context.PEFile.Reader, context.TypeSystem);
-			elementType = ((PointerType)finalStore.Type).ElementType;
 			return true;
 		}