Hi,
David Kastrup <d...@gnu.org> skribis:
> Ludovic Courtès <l...@gnu.org> writes:
[...]
>> Thus we could go with the patch below, though I doubt it would make a
>> measurable difference (and it actually adds tests for other cases).
>
> It made a considerable measurable difference in LilyPond
You measured with and without the patch I sent? Or something else?
>> diff --git a/libguile/eq.c b/libguile/eq.c
>> index 627d6f09b..16c5bfb3f 100644
>> --- a/libguile/eq.c
>> +++ b/libguile/eq.c
>> @@ -303,6 +303,8 @@ scm_equal_p (SCM x, SCM y)
>> return SCM_BOOL_F;
>> if (SCM_IMP (y))
>> return SCM_BOOL_F;
>> + if (scm_is_symbol (x) || scm_is_symbol (y))
>> + return SCM_BOOL_F;
>> if (scm_is_pair (x) && scm_is_pair (y))
>> {
>> if (scm_is_false (scm_equal_p (SCM_CAR (x), SCM_CAR (y))))
>>
>
> Yes, that looks reasonable. scm_is_symbol checks some tag subset that
> the code for equal_p later looks at closer as well: if you worry about
> the extra cost of the scm_is_symbol check, one could try folding the
> symbol check into that later code passage, which would slow down the
> symbol check and effect the more costly fallbacks less. But since those
> fallbacks _are_ more costly, I doubt it would be worth the trouble.
Looking at eq.c, I don’t see what “costly fallbacks” you’re referring
to. For a symbol, AIUI, we end up here:
switch (SCM_TYP7 (x))
{
default:
/* Check equality between structs of equal type (see cell-type test
above). */
if (SCM_STRUCTP (x))
{
if (SCM_INSTANCEP (x))
goto generic_equal;
else
return scm_i_struct_equalp (x, y);
}
break; // <- here, meaning we return SCM_BOOL_F
All the checks leading to this line are type tag comparisons.
Am I overlooking something?
Thanks,
Ludo’.
