Optimize unboxing for nullable #104954
Description
int? Unbox(object o) => (int?)o;Currently generates:
; Method Prog:Foo(System.Object):System.Nullable`1[int] (FullOpts)
G_M28087_IG01:
sub rsp, 40
mov r8, rcx
G_M28087_IG02:
lea rcx, [rsp+0x20]
mov rdx, 0x7FF8318BB750 ; System.Nullable`1[int]
call CORINFO_HELP_UNBOX_NULLABLE
mov rax, qword ptr [rsp+0x20]
G_M28087_IG03:
add rsp, 40
ret
; Total bytes of code: 37we should be able to avoid the unbox helper call here by inlining the fast path. E.g.
Nullable<int> stackLocal;
if (obj == null)
{
stackLocal = {0};
}
else if (obj->pMT == int)
{
stackLocal._hasValue = 1;
stackLocal._value = *((int*)(obj + 8);
}
else
{
CORINFO_HELP_UNBOX_NULLABLE(&stackLocal, obj, clsHandle); // cold fallback (no return?)
}NOTE: no, we can't unbox int? out of boxed uint - it's InvalidCastException so we're fine here.