On Mon, 21 Jun 2021 at 15:02, Richard Henderson <richard.hender...@linaro.org> wrote: > > On 6/21/21 6:51 AM, Peter Maydell wrote: > > On Mon, 21 Jun 2021 at 14:41, Peter Maydell <peter.mayd...@linaro.org> > > wrote: > >> > >> On Mon, 14 Jun 2021 at 09:43, Richard Henderson > >> <richard.hender...@linaro.org> wrote: > >>> > >>> This will eventually simplify front-end usage, and will allow > >>> backends to unset TCG_TARGET_HAS_MEMORY_BSWAP without loss of > >>> optimization. > >>> > >>> The argument is added during expansion, not currently exposed > >>> to the front end translators. Non-zero values are not yet > >>> supported by any backends. > >> > >> Here we say non-zero values are not yet supported by the backend... > > > > Looking at the tcg/README docs, I think what you mean is that > > at the moment all the backends assume/require that the caller passes > > one of TCG_BSWAP_IZ or (TCG_BSWAP_IZ | TCG_BSWAP_OZ), since the > > pre-flags implementation requires the top bytes to be zero and leaves > > them that way. > > Correct. > > > But then the parts of your patch that pass in a zero > > flags word would be wrong... > > The parts that pass in a zero flags word are covered by, from the README: > > > The flags are ignored -- the argument is present > > for consistency with the smaller bswaps.
Ah, I see. If you fix up the commit message, maybe something like # The argument is added during expansion, not currently exposed # to the front end translators. The backends currently only support # a flags value of either TCG_BSWAP_IZ, or (TCG_BSWAP_IZ | TCG_BSWAP_OZ), # since they all require zero top bytes and leave them that way. # At the existing callsites we pass in (TCG_BSWAP_IZ | TCG_BSWAP_OZ), # except for the flags-ignored cases of a 32-bit swap of a 32-bit # value and or a 64-bit swap of a 64-bit value, where we pass 0. then Reviewed-by: Peter Maydell <peter.mayd...@linaro.org> It would be nice to document the actual flag values/names in the user-facing documentation, too. thanks -- PMM
