Fix #1854

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

@@ -379,11 +379,33 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return UseSpan(span);
 		}
 
+		public string GetSpan3()
+		{
+			Span<decimal> span = stackalloc decimal[GetSize()];
+			return UseSpan(span);
+		}
+
+		public string GetSpan4()
+		{
+			Span<decimal> span = stackalloc decimal[4] {
+				1m,
+				2m,
+				3m,
+				4m
+			};
+			return UseSpan(span);
+		}
+
 		public string UseSpan(Span<int> span)
 		{
 			throw new NotImplementedException();
 		}
 
+		public string UseSpan(Span<decimal> span)
+		{
+			throw new NotImplementedException();
+		}
+
 		public int GetSize()
 		{
 			throw new NotImplementedException();

ICSharpCode.Decompiler/IL/PointerArithmeticOffset.cs

@@ -77,6 +77,8 @@ namespace ICSharpCode.Decompiler.IL
 				case KnownTypeCode.UInt64:
 				case KnownTypeCode.Double:
 					return 8;
+				case KnownTypeCode.Decimal:
+					return 16;
 			}
 			return null;
 		}

ICSharpCode.Decompiler/IL/Transforms/ExpressionTransforms.cs

@@ -405,7 +405,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 		{
 			var pointerType = new PointerType(elementType);
 			var elementCountInstr = PointerArithmeticOffset.Detect(sizeInBytesInstr, pointerType.ElementType, checkForOverflow: true, unwrapZeroExtension: true);
-			if (!elementCountInstr.Match(elementCountInstr2).Success)
+			if (elementCountInstr == null || !elementCountInstr.Match(elementCountInstr2).Success)
 				return false;
 			return true;
 		}