On Sun, Oct 10, 2021 at 10:03 PM Florian Weimer <f...@deneb.enyo.de> wrote:
>
> * Fangrui Song:
>
> > An output constraint takes a lvalue. While GCC happily strips the
> > incorrect lvalue to rvalue conversion, Clang rejects the code by default:
> >
> > error: invalid use of a cast in a inline asm context requiring an
> > lvalue: remove the cast or build with -fheinous-gnu-extensions
> >
> > The file appears to share the same origin with gmplib longlong.h but
> > they differ much now (gmplib version is much longer).
> >
> > I don't have write access to the git repo.
> > ---
> > include/longlong.h | 186 ++++++++++++++++++++++-----------------------
> > 1 file changed, 93 insertions(+), 93 deletions(-)
> >
> > diff --git a/include/longlong.h b/include/longlong.h
> > index c3e92e54ecc..0a21a441d2d 100644
> > --- a/include/longlong.h
> > +++ b/include/longlong.h
> > @@ -194,8 +194,8 @@ extern UDItype __udiv_qrnnd (UDItype *, UDItype,
> > UDItype, UDItype);
> > #if defined (__arc__) && W_TYPE_SIZE == 32
> > #define add_ssaaaa(sh, sl, ah, al, bh, bl) \
> > __asm__ ("add.f %1, %4, %5\n\tadc %0, %2, %3" \
> > - : "=r" ((USItype) (sh)), \
> > - "=&r" ((USItype) (sl)) \
> > + : "=r" (sh), \
> > + "=&r" (sl) \
> > : "%r" ((USItype) (ah)), \
> > "rICal" ((USItype) (bh)), \
> > "%r" ((USItype) (al)), \
>
> This seems to alter the meanining of existing programs if sh and sl do
> not have the expected type.
>
> I think you need to add a compound expression and temporaries of type
> USItype if you want to avoid the cast.
Add folks who may comment on the output constraint behavior when a
lvalue to rvalue conversion like (`(USItype)`) is added.
