* Re: [Emacs-diffs] trunk r117007: Optimize cl-struct-slot-value; fix test
[not found] <E1WcRjt-0001M5-8b@vcs.savannah.gnu.org>
@ 2014-04-22 4:34 ` Stefan Monnier
2014-04-22 4:35 ` Daniel Colascione
0 siblings, 1 reply; 3+ messages in thread
From: Stefan Monnier @ 2014-04-22 4:34 UTC (permalink / raw)
To: Daniel Colascione; +Cc: emacs-devel
> - (elt inst (cl-struct-slot-offset struct-type slot-name)))
> + ;; We could use `elt', but since the byte compiler will resolve the
> + ;; branch below at compile time, it's more efficient to use the
> + ;; type-specific accessor.
> + (if (eq (cl-struct-sequence-type struct-type) 'vector)
> + (aref inst (cl-struct-slot-offset struct-type slot-name))
> + (nth (cl-struct-slot-offset struct-type slot-name) inst)))
It won't always resolve the (eq (cl-struct-sequence-type struct-type)
'vector) test at compile-time, tho.
Stefan
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Emacs-diffs] trunk r117007: Optimize cl-struct-slot-value; fix test
2014-04-22 4:34 ` [Emacs-diffs] trunk r117007: Optimize cl-struct-slot-value; fix test Stefan Monnier
@ 2014-04-22 4:35 ` Daniel Colascione
2014-04-22 15:14 ` Stefan Monnier
0 siblings, 1 reply; 3+ messages in thread
From: Daniel Colascione @ 2014-04-22 4:35 UTC (permalink / raw)
To: Stefan Monnier; +Cc: emacs-devel
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On 04/21/2014 09:34 PM, Stefan Monnier wrote:
>> - (elt inst (cl-struct-slot-offset struct-type slot-name)))
>> + ;; We could use `elt', but since the byte compiler will resolve the
>> + ;; branch below at compile time, it's more efficient to use the
>> + ;; type-specific accessor.
>> + (if (eq (cl-struct-sequence-type struct-type) 'vector)
>> + (aref inst (cl-struct-slot-offset struct-type slot-name))
>> + (nth (cl-struct-slot-offset struct-type slot-name) inst)))
>
> It won't always resolve the (eq (cl-struct-sequence-type struct-type)
> 'vector) test at compile-time, tho.
It did in my tests, when struct-type was a symbol. When struct-type is
something that might vary, the branch shows up in the bytecode. Maybe
the comment should say "will resolve...when possible".
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Emacs-diffs] trunk r117007: Optimize cl-struct-slot-value; fix test
2014-04-22 4:35 ` Daniel Colascione
@ 2014-04-22 15:14 ` Stefan Monnier
0 siblings, 0 replies; 3+ messages in thread
From: Stefan Monnier @ 2014-04-22 15:14 UTC (permalink / raw)
To: Daniel Colascione; +Cc: emacs-devel
>> It won't always resolve the (eq (cl-struct-sequence-type struct-type)
>> 'vector) test at compile-time, tho.
> It did in my tests, when struct-type was a symbol.
Yes, it does for the case where we could have used the accessor instead
(tho I understand there are cases where using the accessor is impractical).
But I'm not convinced this should be a common case.
> When struct-type is something that might vary, the branch shows up in
> the bytecode.
Not only the branch but the cl-struct-sequence-type call as well.
Ends up much more expansive than an `elt'.
I used `elt' in my original code because my benchmark made me think that
replacing `elt' with `aref' is not worth the extra cost when we can't do
that (the speed difference just for the elt/aref call is less than 10%,
which gets drowned in the noise when you add the typep test; for the
setter, the impact is a bit higher since we end up adding a listp test
which can't be optimized away (contrary to your test), but there again,
the difference is pretty small in practice).
Anyway, either code is fine. I just wanted to share the results of
my benchmarketting.
Stefan
^ permalink raw reply [flat|nested] 3+ messages in thread
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[not found] <E1WcRjt-0001M5-8b@vcs.savannah.gnu.org>
2014-04-22 4:34 ` [Emacs-diffs] trunk r117007: Optimize cl-struct-slot-value; fix test Stefan Monnier
2014-04-22 4:35 ` Daniel Colascione
2014-04-22 15:14 ` Stefan Monnier
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