From: Paul Eggert <eggert@cs.ucla.edu>
To: Stefan Monnier <monnier@IRO.UMontreal.CA>
Cc: 11935@debbugs.gnu.org
Subject: bug#11935: XINT etc. should be functions
Date: Tue, 24 Jul 2012 21:07:28 -0700 [thread overview]
Message-ID: <500F7100.9080407@cs.ucla.edu> (raw)
In-Reply-To: <jwvzk6oesd7.fsf-monnier+emacs@gnu.org>
On 07/24/2012 02:57 PM, Stefan Monnier wrote:
> It seems to define XLI first as
> a macro then as a function. Is that right?
Yes. The macro is purely for performance with -O0.
The function is for all other purposes, including
having XLI work in expressions given to GDB.
> why is it any better than using only the macro form?
Mostly for debuggability, though there's also a small
performance win when compiling with default (-O2)
optimization. Having the functions makes GDB more useful
when printing expressions. Here's a trivial example:
(gdb) p SYMBOLP (Qnil)
$3 = 1
With the patch, this works if one compiles with -g -O0,
regardless of whether -DINLINING=0 is also specified.
This is because SYMBOLP is defined as a function,
regardless of whether it is also defined as a macro.
Also, having the functions makes backtraces work better,
even when compiling with default optimization. For example,
here's the start of a GDB backtrace of a patched Emacs
compiled with default optimization:
(gdb) where
#0 XTYPE (a=0) at lisp.h:461
#1 VECTORLIKEP (x=0) at lisp.h:2018
#2 PSEUDOVECTORP (code=2, a=0) at lisp.h:2080
#3 PROCESSP (a=0) at lisp.h:2102
#4 Fget_process (name=0) at process.c:680
#5 0x0000000000573e87 in eval_sub (form=form@entry=16514534) at eval.c:2146
...
When the macro forms are used, levels #0 through #3 are lost,
which makes things harder to follow, particularly when one
is not expert in the code.
This debuggability win is partly lost when compiling with
plain -O0, because then some functions turn into macros.
But that's OK, since one can compile with -O0 -DINLINING=0
to get nicer debugging.
next prev parent reply other threads:[~2012-07-25 4:07 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-13 15:07 bug#11935: XINT etc. should be functions Paul Eggert
2012-07-14 2:20 ` bug#11935: [TRUNCATED MESSAGE 2746 87596] " Richard Stallman
2012-07-15 13:41 ` Paul Eggert
2012-07-15 22:06 ` Stefan Monnier
2012-07-16 14:54 ` Paul Eggert
2012-07-16 16:12 ` Eli Zaretskii
2012-07-16 21:40 ` Paul Eggert
2012-07-16 18:19 ` Richard Stallman
2012-07-16 22:46 ` Paul Eggert
2012-07-17 3:04 ` Eli Zaretskii
2012-07-17 3:54 ` Paul Eggert
2012-07-24 2:20 ` Paul Eggert
2012-07-24 9:07 ` Stefan Monnier
2012-07-24 13:45 ` Paul Eggert
2012-07-24 21:57 ` Stefan Monnier
2012-07-25 4:07 ` Paul Eggert [this message]
2012-07-15 14:41 ` Chong Yidong
2012-07-15 16:40 ` Paul Eggert
2012-07-16 2:22 ` Chong Yidong
2012-07-16 14:54 ` Paul Eggert
2013-06-06 15:56 ` Paul Eggert
2013-06-06 16:36 ` Andreas Schwab
2013-06-13 16:30 ` Paul Eggert
2013-06-06 16:42 ` Stefan Monnier
2013-06-09 0:52 ` Paul Eggert
2013-06-09 3:04 ` Stefan Monnier
2013-06-09 4:37 ` James Cloos
2013-06-09 6:59 ` Jan Djärv
2013-06-09 7:13 ` Paul Eggert
2013-06-09 15:57 ` Stefan Monnier
2013-06-13 14:45 ` Paul Eggert
2013-06-13 20:08 ` Stefan Monnier
2013-06-15 6:43 ` Paul Eggert
2013-06-15 14:22 ` Stefan Monnier
2013-06-17 6:05 ` Paul Eggert
2013-06-09 6:56 ` Jan Djärv
2013-06-09 7:23 ` Paul Eggert
2013-06-09 9:18 ` Jan Djärv
2013-06-09 14:25 ` Juanma Barranquero
2013-06-09 16:05 ` Jan Djärv
2013-06-10 13:40 ` Barry OReilly
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