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Re: [Emacs-diffs] master 81a1088: Tweak builtin symbol order for speed
From: |
Pip Cet |
Subject: |
Re: [Emacs-diffs] master 81a1088: Tweak builtin symbol order for speed |
Date: |
Fri, 12 Jul 2019 07:12:42 +0000 |
On Fri, Jul 12, 2019 at 6:07 AM Paul Eggert <address@hidden> wrote:
> branch: master
> commit 81a1088ee8b833cd30a3363782195d6c4d575672
> Author: Paul Eggert <address@hidden>
> Commit: Paul Eggert <address@hidden>
>
> Tweak builtin symbol order for speed
>
> * lib-src/make-docfile.c (compare_globals):
> Make symbols 1 through 4 be t, unbound, error, lambda.
> This is in addition to symbol 0 being nil.
> This change improved ‘make compile-always’ performance by 0.6%
> on my platform.
Hmm. I don't understand why this would improve performance this
significantly (maybe because it allows 8-bit offsets to be used rather
than 32-bit ones?). It will make debugging a tad easier, though.
XIL(0x30) for Qt is easy to remember.
Maybe it would be a good idea to make Vdead a symbol (or a tagged NULL
pointer) and treat it similarly, if this actually improves
performance.
> ---> lib-src/make-docfile.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
> index 4d25b0a..368150b 100644
> --- a/lib-src/make-docfile.c
> +++ b/lib-src/make-docfile.c
> @@ -641,13 +641,24 @@ compare_globals (const void *a, const void *b)
> return ga->type - gb->type;
>
> /* Consider "nil" to be the least, so that iQnil is zero. That
> - way, Qnil's internal representation is zero, which is a bit faster. */
> + way , Qnil's internal representation is zero, which is a bit faster.
> + Similarly, consideer "t" to be the second-least, and so forth. */
"consider"
> if (ga->type == SYMBOL)
> {
> - bool a_nil = strcmp (ga->name, "Qnil") == 0;
> - bool b_nil = strcmp (gb->name, "Qnil") == 0;
> - if (a_nil | b_nil)
> - return b_nil - a_nil;
> + /* Common symbols in decreasing popularity order. */
> + static char const commonsym[][8]
I'm curious, why isn't this simply "static char *commonsym[]"?