Remove unnecessary cast for num elements expression (#72302)

Author: elinor-fung

src/libraries/System.Runtime.InteropServices/gen/Microsoft.Interop.SourceGeneration/Marshalling/AttributedMarshallingModelGeneratorFactory.cs

@@ -79,25 +79,40 @@ public IMarshallingGenerator Create(TypePositionInfo info, StubCodeContext conte
 
         private ExpressionSyntax GetNumElementsExpressionFromMarshallingInfo(TypePositionInfo info, CountInfo count, StubCodeContext context)
         {
-            return count switch
+            switch (count)
             {
-                SizeAndParamIndexInfo(int size, SizeAndParamIndexInfo.UnspecifiedParam) => GetConstSizeExpression(size),
-                ConstSizeCountInfo(int size) => GetConstSizeExpression(size),
-                SizeAndParamIndexInfo(SizeAndParamIndexInfo.UnspecifiedConstSize, TypePositionInfo param) => CheckedExpression(SyntaxKind.CheckedExpression, GetExpressionForParam(param)),
-                SizeAndParamIndexInfo(int size, TypePositionInfo param) => CheckedExpression(SyntaxKind.CheckedExpression, BinaryExpression(SyntaxKind.AddExpression, GetConstSizeExpression(size), GetExpressionForParam(param))),
-                CountElementCountInfo(TypePositionInfo elementInfo) => CheckedExpression(SyntaxKind.CheckedExpression, GetExpressionForParam(elementInfo)),
-                _ => throw new MarshallingNotSupportedException(info, context)
+                case SizeAndParamIndexInfo(int size, SizeAndParamIndexInfo.UnspecifiedParam):
+                    return GetConstSizeExpression(size);
+                case ConstSizeCountInfo(int size):
+                    return GetConstSizeExpression(size);
+                case SizeAndParamIndexInfo(SizeAndParamIndexInfo.UnspecifiedConstSize, TypePositionInfo param):
                 {
-                    NotSupportedDetails = SR.ArraySizeMustBeSpecified
-                },
-            };
+                    ExpressionSyntax expr = GetExpressionForParam(param, out bool isIntType);
+                    return isIntType ? expr : CheckedExpression(SyntaxKind.CheckedExpression, expr);
+                }
+                case SizeAndParamIndexInfo(int size, TypePositionInfo param):
+                    return CheckedExpression(SyntaxKind.CheckedExpression,
+                        BinaryExpression(SyntaxKind.AddExpression,
+                            GetConstSizeExpression(size),
+                            GetExpressionForParam(param, out _)));
+                case CountElementCountInfo(TypePositionInfo elementInfo):
+                {
+                    ExpressionSyntax expr = GetExpressionForParam(elementInfo, out bool isIntType);
+                    return isIntType ? expr : CheckedExpression(SyntaxKind.CheckedExpression, expr);
+                }
+                default:
+                    throw new MarshallingNotSupportedException(info, context)
+                    {
+                        NotSupportedDetails = SR.ArraySizeMustBeSpecified
+                    };
+            }
 
             static LiteralExpressionSyntax GetConstSizeExpression(int size)
             {
                 return LiteralExpression(SyntaxKind.NumericLiteralExpression, Literal(size));
             }
 
-            ExpressionSyntax GetExpressionForParam(TypePositionInfo paramInfo)
+            ExpressionSyntax GetExpressionForParam(TypePositionInfo paramInfo, out bool isIntType)
             {
                 ExpressionSyntax numElementsExpression = GetIndexedNumElementsExpression(
                            context,
@@ -132,7 +147,10 @@ ExpressionSyntax GetExpressionForParam(TypePositionInfo paramInfo)
                     };
                 }
 
-                return CastExpression(
+                isIntType = specialType.SpecialType == SpecialType.System_Int32;
+                return isIntType
+                    ? numElementsExpression
+                    : CastExpression(
                         PredefinedType(Token(SyntaxKind.IntKeyword)),
                         ParenthesizedExpression(numElementsExpression));
             }