Re: [PATCH 2/2] xdiff: optimize xdl_hash_record_verbatim

> Alexander Monakov <amonakov@ispras.ru> writes:
> 
> > +/*
> > + * Compiler reassociation barrier: pretend to modify X and Y to disallow
> > + * changing evaluation order with respect to following uses of X and Y.
> > + */
> > +#ifdef __GNUC__
> > +#define REASSOC_FENCE(x, y) asm("" : "+r"(x), "+r"(y))
> > +#else
> > +#define REASSOC_FENCE(x, y)
> > +#endif
> 
> With gcc we can build, but with clang, we unfortunately get this:
> 
>     $ make CC=clang DEVELOPER=YesPlease
>     xdiff/xutils.c:330:4: error: extension used [-Werror,-Wlanguage-extension-token]
>       330 |                         REASSOC_FENCE(c0, ha);
>           |                         ^
>     xdiff/xutils.c:302:29: note: expanded from macro 'REASSOC_FENCE'
>       302 | #define REASSOC_FENCE(x, y) asm("" : "+r"(x), "+r"(y))
>           |                             ^