GNU bug report logs - #68267
[PATCH] maint: add attributes to two functions without side effects

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Pádraig Brady <P <at> draigBrady.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#68267: closed ([PATCH] maint: add attributes to two functions
 without side effects)
Date: Sat, 06 Jan 2024 15:35:01 +0000

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Your message dated Sat, 6 Jan 2024 15:34:07 +0000
with message-id <8f5a4d0c-4cd7-02ae-e48a-e2a8fa71e3e6 <at> draigBrady.com>
and subject line Re: bug#68267: [PATCH] maint: add attributes to two functions without side effects
has caused the debbugs.gnu.org bug report #68267,
regarding [PATCH] maint: add attributes to two functions without side effects
to be marked as done.

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-- 
68267: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=68267
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From: Samuel Tardieu <sam <at> rfc1149.net>
To: bug-coreutils <at> gnu.org
Cc: Samuel Tardieu <sam <at> rfc1149.net>
Subject: [PATCH] maint: add attributes to two functions without side effects
Date: Fri,  5 Jan 2024 17:44:06 +0100

* src/date.c (res_width): This function computes its result solely
from the value of its parameter and qualifies for the const attribute.
* src/tee.c (get_next_out): This function has no side effect and
qualifies for the pure attribute.

Those two functions were flagged by GCC 12.3.0.
---
Resent here, I sent it to the coreutils@ mailing-list while the hacking
doc says to send it here.

 src/date.c | 1 +
 src/tee.c  | 1 +
 2 files changed, 2 insertions(+)

diff --git a/src/date.c b/src/date.c
index 39fc0715d..03bf012e2 100644
--- a/src/date.c
+++ b/src/date.c
@@ -294,6 +294,7 @@ Show the local time for 9AM next Friday on the west coast of the US\n\
 /* Yield the number of decimal digits needed to output a time with the
    nanosecond resolution RES, without losing information.  */
 
+ATTRIBUTE_CONST
 static int
 res_width (long int res)
 {
diff --git a/src/tee.c b/src/tee.c
index 07d525c95..eb074427c 100644
--- a/src/tee.c
+++ b/src/tee.c
@@ -185,6 +185,7 @@ main (int argc, char **argv)
 /* Return the index of the first non-null descriptor after idx,
    or -1 if all are null.  */
 
+ATTRIBUTE_PURE
 static int
 get_next_out (FILE **descriptors, int nfiles, int idx)
 {
-- 
2.42.0

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From: Pádraig Brady <P <at> draigBrady.com>
To: Samuel Tardieu <sam <at> rfc1149.net>, 68267-done <at> debbugs.gnu.org
Subject: Re: bug#68267: [PATCH] maint: add attributes to two functions without
 side effects
Date: Sat, 6 Jan 2024 15:34:07 +0000

On 05/01/2024 16:44, Samuel Tardieu wrote:
> * src/date.c (res_width): This function computes its result solely
> from the value of its parameter and qualifies for the const attribute.
> * src/tee.c (get_next_out): This function has no side effect and
> qualifies for the pure attribute.
> 
> Those two functions were flagged by GCC 12.3.0.

I'm guessing GCC 12 needs help here as it can't determine the loops are finite.
(as per: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109914 )

Though I'm not seeing this suggestion with GCC 13.2.1,
so perhaps GCC 12 can determine the loops are finite?

I'll apply this since GCC 13 is less that a year old,
but in general we try to avoid littering code like this.

thanks,
Pádraig

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