On Sat, Nov 7, 2020 at 10:38 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I think there's a couple of others, like
>
> SEL(x, x, 0) -> x
>
> which looks insane, but I think these are the kinds of things that end
> up showing up when you inline things that return errors, and then you
> test them for zero etc.
Made-up crazy example:
extern int fn(int);
int t(int x)
{
int err = fn(x);
if (err)
return err;
return 0;
}
which is the kind of thing that can happen when you have various
config options and code goes away. It *should* just result in a no-op
(ie just call 'fn()' and return its value), but currently sparse
generates
call.32 %r2 <- fn, %arg1
select.32 %r6 <- %r2, %r2, $0
ret.32 %r6
instead of
call.32 %r2 <- fn, %arg1
ret.32 %r2
but I hadn't actually applied your patches when I did that test, so
maybe you had caught this case already without me realizing it.
Linus
