NAOT: fold "always false" typechecks #97601
Description
If an interface/abstract class has no subclasses or they were trimmed out - all typechecks against that subclass should be folded, e.g.:
interface IMyInterface { }
class Program
{
static void Main()
{
Test(null);
}
[MethodImpl(MethodImplOptions.NoInlining)]
static void Test(object o)
{
if (o is IMyInterface) // there are no types implementing this interface
Console.WriteLine("MyInterface!");
}
}Current codegen with NativeAOT for Test:
; Assembly listing for method Program:Test(System.Object) (FullOpts)
sub rsp, 40
mov rdx, rcx
lea rcx, [(reloc 0x4000000000422e10)] ; IMyInterface
call CORINFO_HELP_ISINSTANCEOFINTERFACE
test rax, rax
je SHORT G_M3485_IG04
lea rcx, gword ptr [(reloc 0x4000000000422e28)] ; '"MyInterface!"'
call System.Console:WriteLine(System.String)
G_M3485_IG04:
nop
add rsp, 40
ret
; Total bytes of code 42Expected codegen:
; Assembly listing for method Program:Test(System.Object) (FullOpts)
ret
; Total bytes of code 1,cc @MichalStrehovsky. I presume for that we need to make 0 a meaningful result for getExactClasses API.