Re: [Qemu-devel] [PATCH v2] target/xtensa: rework zero overhead loops implementation

[Max Filippov]

On Fri, Jan 11, 2019 at 2:17 PM Richard Henderson
<address@hidden> wrote:
>
> On 1/12/19 9:14 AM, Max Filippov wrote:
> >>> +        /*
> >>> +         * 0 in the csbase_lend field means that there may not be a 
> >>> loopback
> >>> +         * for any instruction that starts inside this page. Any other 
> >>> value
> >>> +         * means that an instruction that ends at this offset from the 
> >>> page
> >>> +         * start may loop back.
> >>
> >> Nit: s/may/will/g
> >>
> >> Using "may" makes it seem like we may have missed a case that should have
> >> looped back.
> >
> > Using "will" makes it seem like it always loops back, but it doesn't do it
> > when LCOUNT is 0.
>
> Err, no, you covered that in the first sentence, where 0 means that it will 
> not
> loop back.

What I'm saying is that "Any other value means that an instruction that ends
at this offset from the page start will loop back." sounds like that instruction
will loop back unconditionally. LCOUNT = 0 is the condition when this doesn't
happen, and it's not encoded in the TB flags. It's checked in the generated
loopback code.

-- 
Thanks.
-- Max