Re: [PATCH v4 06/57] accel/tcg: Honor atomicity of loads

[Peter Maydell]

On Tue, 9 May 2023 at 15:27, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 5/9/23 13:04, Peter Maydell wrote:
> >> If the LDP is aligned mod 8, but not aligned mod 16, then both 8-byte 
> >> operations must be
> >> (separately) atomic, and we return MO_64.
> >
> > So there's an implicit "at most 2 atomic sub-operations
> > inside a WITHIN16 load" restriction? i.e. you can't
> > use WITHIN16 to say "do this 8 byte load atomically but
> > if it's not in a 16-byte region do it with 4 2-byte loads",
> > even though in theory MO_ATOM_WITHIN16 | MO_ATMAX_2 | MO_8
> > would describe that ?
>
> Correct on both counts.  While you're right that this is a valid 
> generalization, it's not
> something for which I've found a use case.

Yeah, that's fine -- but we should note the restrictions/
requirements in the doc comment for WITHIN16. (And maybe
an assert somewhere if there's somewhere convenient to
put it?)

thanks
-- PMM