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* [Bug middle-end/44321] attribute warn_unused_result fails under inlining.
2010-05-29 11:33 [Bug middle-end/44321] New: attribute warn_unused_result fails under inlining davek at gcc dot gnu dot org
@ 2010-05-29 11:33 ` davek at gcc dot gnu dot org
2010-05-29 11:40 ` rguenth at gcc dot gnu dot org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: davek at gcc dot gnu dot org @ 2010-05-29 11:33 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from davek at gcc dot gnu dot org 2010-05-29 11:33 -------
Created an attachment (id=20771)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=20771&action=view)
testcase as per initial comment.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44321
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/44321] New: attribute warn_unused_result fails under inlining.
@ 2010-05-29 11:33 davek at gcc dot gnu dot org
2010-05-29 11:33 ` [Bug middle-end/44321] " davek at gcc dot gnu dot org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: davek at gcc dot gnu dot org @ 2010-05-29 11:33 UTC (permalink / raw)
To: gcc-bugs
In the (to-be) attached testcase, GCC warns about an unused result when the
return value of the function is ignored, or cast to void, but it fails to warn
when the cast-to-void is hidden inside an inline function, like so:
$ cat -n wur.c
1
2 static inline void ignore_value (int i) { (void) i; }
3
4 extern int foo (void) __attribute__ ((warn_unused_result));
5
6 void bar1 (void)
7 {
8 foo ();
9 }
10
11 void bar2 (void)
12 {
13 (void) foo ();
14 }
15
16 void bar3 (void)
17 {
18 ignore_value (foo ());
19 }
$ gcc-4 -c wur.c -o wur.o --save-temps -W -Wall -Wextra
wur.c: In function 'bar2':
wur.c:13:3: warning: ignoring return value of 'foo', declared with attribute
war
n_unused_result [-Wunused-result]
wur.c: In function 'bar1':
wur.c:8:7: warning: ignoring return value of 'foo', declared with attribute
warn
_unused_result [-Wunused-result]
This happens at all -O levels. I haven't filled in the host/target/build
triplets because I don't suppose it is in any way specific to any of them.
BTW, it's interesting that the warnings come out in reverse order, is that
supposed to happen?
--
Summary: attribute warn_unused_result fails under inlining.
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: davek at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44321
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/44321] attribute warn_unused_result fails under inlining.
2010-05-29 11:33 [Bug middle-end/44321] New: attribute warn_unused_result fails under inlining davek at gcc dot gnu dot org
2010-05-29 11:33 ` [Bug middle-end/44321] " davek at gcc dot gnu dot org
@ 2010-05-29 11:40 ` rguenth at gcc dot gnu dot org
2010-05-29 17:32 ` bonzini at gnu dot org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2010-05-29 11:40 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from rguenth at gcc dot gnu dot org 2010-05-29 11:40 -------
You can add
void bar4 (void)
{
int dummy;
dummy = foo ();
}
so I'm not sure the ignore_value () function call isn't a use. In fact
if you externalize that function it is at least a possible use.
Which also raises the question whether (void) is really more "ignoring"
the result than the assignment to a dummy variable.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44321
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/44321] attribute warn_unused_result fails under inlining.
2010-05-29 11:33 [Bug middle-end/44321] New: attribute warn_unused_result fails under inlining davek at gcc dot gnu dot org
2010-05-29 11:33 ` [Bug middle-end/44321] " davek at gcc dot gnu dot org
2010-05-29 11:40 ` rguenth at gcc dot gnu dot org
@ 2010-05-29 17:32 ` bonzini at gnu dot org
2010-05-29 17:46 ` rguenth at gcc dot gnu dot org
2010-05-30 6:43 ` bonzini at gnu dot org
4 siblings, 0 replies; 6+ messages in thread
From: bonzini at gnu dot org @ 2010-05-29 17:32 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from bonzini at gnu dot org 2010-05-29 17:32 -------
I don't think this bug is of any use. Unlike nonnull, unused return values do
not trigger undesirable optimizations and (as far as I can tell) cannot
possibly result in miscompilation.
This bug is indeed about a loophole, and one that could indeed cause some bugs
(even security bugs). But, fixing it would also make it impossible for many
projects to use -Werror, since they have to deal with the fact that __wur was
used inappropriately by glibc.
Adding another attribute and making __wur overridable BTW would not be a
solution since glibc would certainly switch to the new __really_wur attribute
and we'd be in the same situation. :-)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44321
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/44321] attribute warn_unused_result fails under inlining.
2010-05-29 11:33 [Bug middle-end/44321] New: attribute warn_unused_result fails under inlining davek at gcc dot gnu dot org
` (2 preceding siblings ...)
2010-05-29 17:32 ` bonzini at gnu dot org
@ 2010-05-29 17:46 ` rguenth at gcc dot gnu dot org
2010-05-30 6:43 ` bonzini at gnu dot org
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2010-05-29 17:46 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from rguenth at gcc dot gnu dot org 2010-05-29 17:46 -------
(In reply to comment #3)
> I don't think this bug is of any use. Unlike nonnull, unused return values do
> not trigger undesirable optimizations and (as far as I can tell) cannot
> possibly result in miscompilation.
>
> This bug is indeed about a loophole, and one that could indeed cause some bugs
> (even security bugs). But, fixing it would also make it impossible for many
> projects to use -Werror, since they have to deal with the fact that __wur was
> used inappropriately by glibc.
>
> Adding another attribute and making __wur overridable BTW would not be a
> solution since glibc would certainly switch to the new __really_wur attribute
> and we'd be in the same situation. :-)
True, but if int dummy = foo() works then we can also make (void) foo ()
work.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44321
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug middle-end/44321] attribute warn_unused_result fails under inlining.
2010-05-29 11:33 [Bug middle-end/44321] New: attribute warn_unused_result fails under inlining davek at gcc dot gnu dot org
` (3 preceding siblings ...)
2010-05-29 17:46 ` rguenth at gcc dot gnu dot org
@ 2010-05-30 6:43 ` bonzini at gnu dot org
4 siblings, 0 replies; 6+ messages in thread
From: bonzini at gnu dot org @ 2010-05-30 6:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from bonzini at gnu dot org 2010-05-30 06:42 -------
Richi, I think we're saying the same thing from two different directions.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44321
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2010-05-30 6:43 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2010-05-29 11:33 [Bug middle-end/44321] New: attribute warn_unused_result fails under inlining davek at gcc dot gnu dot org
2010-05-29 11:33 ` [Bug middle-end/44321] " davek at gcc dot gnu dot org
2010-05-29 11:40 ` rguenth at gcc dot gnu dot org
2010-05-29 17:32 ` bonzini at gnu dot org
2010-05-29 17:46 ` rguenth at gcc dot gnu dot org
2010-05-30 6:43 ` bonzini at gnu dot org
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