[JIT] Recognize when length is never negative for Span<T>::.ctor(void*, int32) #119466
Description
static unsafe Span<byte> M1(byte* p, int b) => new(p, (byte)b);
static unsafe Span<byte> M2(byte* p, byte b) => new(p, b);; Core CLR 9.0.525.21509 on x64
C.M1(Byte*, Int32)
L0000: sub rsp, 0x28
L0004: movzx eax, r8b
L0008: test eax, eax
L000a: jl short L001a
L000c: mov [rcx], rdx
L000f: mov [rcx+8], eax
L0012: mov rax, rcx
L0015: add rsp, 0x28
L0019: ret
L001a: mov rax, 0x7ffebaa16d00
L0024: call qword ptr [rax]
L0026: int3
C.M2(Byte*, Byte)
L0000: movzx eax, r8b
L0004: mov [rcx], rdx
L0007: mov [rcx+8], eax
L000a: mov rax, rcx
L000d: retcodgen: sharplab.io, godbolt.org
References: #83248