'ConvertOrWidenPrimitivesEnumsAndPointersIfPossible' in NativeAOT is unnecessarily rooting 'BigInteger' (and a bunch more stuff) due to 'Convert.*' calls

[Sergio0694]

While working on reducing the size for WinRT component using NativeAOT, we found some numeric stuff being kept:

Quoting @MichalStrehovsky on Discord:

"Looks like the Convert.ToSingle call in ConvertOrWidenPrimitivesEnumsAndPointersIfPossible is an overkill, we don't need code to parse floats since conversion from string to single would have been disallowed"

This is the entire set that needs to be supported:

runtime/src/coreclr/nativeaot/System.Private.CoreLib/src/System/InvokeUtils.cs

Lines 225 to 242 in fcc2408

	ReadOnlySpan<ushort> primitiveAttributes = [
	0x0000, // Unknown
	0x0000, // Void
	0x0004, // Boolean (W = BOOL)
	0xCf88, // Char (W = U2, CHAR, I4, U4, I8, U8, R4, R8)
	0xC550, // SByte (W = I1, I2, I4, I8, R4, R8)
	0xCFE8, // Byte (W = CHAR, U1, I2, U2, I4, U4, I8, U8, R4, R8)
	0xC540, // Int16 (W = I2, I4, I8, R4, R8)
	0xCF88, // UInt16 (W = U2, CHAR, I4, U4, I8, U8, R4, R8)
	0xC500, // Int32 (W = I4, I8, R4, R8)
	0xCE00, // UInt32 (W = U4, I8, R4, R8)
	0xC400, // Int64 (W = I8, R4, R8)
	0xC800, // UInt64 (W = U8, R4, R8)
	0x0000, // IntPtr
	0x0000, // UIntPtr
	0xC000, // Single (W = R4, R8)
	0x8000, // Double (W = R8)
	];

. Calling into convert just calls IConvertible methods so instead of the subset, one gets conversions from everything that was allocated in the app and supports IConvertible (that's why you get string -> double conversions). I don't know if there's a better mechanism in the BCL. One could just inline conversions for the whole matrix since there is an upper bound but that may not pass Jan's code review. If you can find a more narrow codepath in the BCL that handles the subset, that would be a good fix"

Opening this issue for tracking. @jkotas do you happen to know whether there's already some helper we can reuse here, or do you have any suggestions on how we could remove that dependency on Convert.* calls? Would hardcoding all possible combinations be acceptable, or something else? 🙂

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[jkotas]

We have number of copies of the wideling algorithm both in managed code

runtime/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Array.NativeAot.cs

Line 506 in af889b9

private static unsafe void CopyImplPrimitiveTypeWithWidening(Array sourceArray, int sourceIndex, Array destinationArray, int destinationIndex, int length, bool reliable)

runtime/src/coreclr/nativeaot/System.Private.CoreLib/src/System/InvokeUtils.cs

Line 102 in af889b9

private static Exception ConvertOrWidenPrimitivesEnumsAndPointersIfPossible(object srcObject, MethodTable* dstEEType, CheckArgumentSemantics semantics, out object? dstObject)

runtime/src/coreclr/System.Private.CoreLib/src/System/Array.CoreCLR.cs

Line 234 in af889b9

private static unsafe void CopyImplPrimitiveWiden(Array sourceArray, int sourceIndex, Array destinationArray, int destinationIndex, int length)

runtime/src/libraries/System.Private.CoreLib/src/System/Reflection/InvokeUtils.cs

Line 14 in af889b9

public static object ConvertOrWiden(RuntimeType srcType, object srcObject, RuntimeType dstType, CorElementType dstElementType)

And several more in native code.

Avoiding IConvertible,in in the native AOT implementations sounds good to me if it is only ever used for primitives. Bonus points for making the different implementations more uniform. Physically sharing the code may be too hard - I am not sure.