Re: struct optimizations

[Ludovic Courtès]

Hi Andy,

Andy Wingo <address@hidden> writes:

> Some comments:
>
>     -#define SCM_VTABLE_FLAG_RESERVED_0 (1L << 5)
>     -#define SCM_VTABLE_FLAG_RESERVED_1 (1L << 6)
>     +#define SCM_VTABLE_FLAG_SIMPLE (1L << 5) /* instances of this vtable 
> have only "pr" fields */
>     +#define SCM_VTABLE_FLAG_SIMPLE_RW (1L << 6) /* instances of this vtable 
> have only "pw" fields */
>
> The comments do not appear to be correct, given a later check:
>
>     +  if (SCM_LIKELY (SCM_VTABLE_FLAG_IS_SET (vtable, SCM_VTABLE_FLAG_SIMPLE)
>     +                   && SCM_VTABLE_FLAG_IS_SET (vtable, 
> SCM_VTABLE_FLAG_SIMPLE_RW)
>     +                   && p < SCM_STRUCT_DATA_REF (vtable, 
> scm_vtable_index_size)))
>     +    /* The fast path: HANDLE is a struct with only "p" fields.  */
>     +    data[p] = SCM_UNPACK (val);
>
> It seems that currently SIMPLE is for all pr *or* all pw slots.

True.

> But we should be more orthogonal than that; let's have SIMPLE be for
> having all slots be readable p slots. (Note that this still allows a
> mix of readable and writable slots.)
>
> Then perhaps we can change SIMPLE_RW to be MUTABLE or something, to
> indicate that all slots of this object are mutable.
>
> What do you think?

I agree and I’ll look into it.

Thanks for the review!

Ludo’.