Re: [Emacs-diffs] trunk r117897: Port USE_LOCAL_ALLOCATORS code to clang 3.4 x86-64.

[Stefan Monnier]

> +/* Alignment fixup needed for alloca.  GCC aligns alloca properly already,
> +   Clang sometimes doesn't, and play it safe for other random compilers.  */
> +# if __GNUC__ && !__clang__
> +enum { ALLOCA_FIXUP = 0 };
> +# else
> +enum { ALLOCA_FIXUP = GCALIGNMENT - 1 };
> +# endif
> +
> +/* Declare a void * variable PTR and set it to a properly-aligned array of
> +   N newly allocated bytes with function lifetime.  */
> +# define LOCAL_ALLOCA(ptr, n)                                \
> +    void *ptr = alloca ((n) + ALLOCA_FIXUP);         \
> +    ptr = (void *) ((intptr_t) ptr_ & ~(ALLOCA_FIXUP))

I find this hideous.  I'd prefer we just don't use alloca in
those cases where alignment would be a problem.


        Stefan