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* [Bug c/50021] New: -Wsuggest-attribute=pure makes obviously-incorrect suggestion
@ 2011-08-08 7:16 eggert at gnu dot org
2011-08-08 10:14 ` [Bug tree-optimization/50021] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: eggert at gnu dot org @ 2011-08-08 7:16 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
Summary: -Wsuggest-attribute=pure makes obviously-incorrect
suggestion
Product: gcc
Version: 4.6.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: eggert@gnu.org
Created attachment 24948
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24948
v.i - input that causes GCC to generate incorrect warning
I ran into this problem when building coreutils (git master) using
GCC 4.6.1, x86-64, on Fedora 14.
For the attached program v.i, "gcc -Wsuggest-attribute=pure -O2 -S v.i" says:
v.i:3546:1: warning: function might be candidate for attribute 'pure' if it
is known to return normally [-Wsuggest-attribute=pure]
But the function in question is obviously not pure:
static void
advance (_Bool f)
{
++pos;
if (f && pos >= argc)
beyond ();
}
as it starts off with a side effect (adding 1 to the static variable 'pos').
Here's the output of "gcc -v -save-temps -Wsuggest-attribute=pure -O2 -S v.i":
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.6.1/configure
--prefix=/home/eggert/opt/Linux-x86_64/gcc-4.6.1 --disable-nls
Thread model: posix
gcc version 4.6.1 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wsuggest-attribute=pure' '-O2' '-S'
'-mtune=generic' '-march=x86-64'
/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/cc1
-fpreprocessed v.i -quiet -dumpbase v.i -mtune=generic -march=x86-64 -auxbase v
-O2 -Wsuggest-attribute=pure -version -o v.s
GNU C (GCC) version 4.6.1 (x86_64-unknown-linux-gnu)
compiled by GNU C version 4.6.1, GMP version 4.3.1, MPFR version 2.4.2,
MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (GCC) version 4.6.1 (x86_64-unknown-linux-gnu)
compiled by GNU C version 4.6.1, GMP version 4.3.1, MPFR version 2.4.2,
MPC version 0.8.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: b0a4f47793c670c0e36c6193e4fd175b
v.i:3546:1: warning: function might be candidate for attribute 'pure' if it
is known to return normally [-Wsuggest-attribute=pure]
COMPILER_PATH=/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/libexec/gcc/x86_64-unknown-linux-gnu/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/
LIBRARY_PATH=/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/home/eggert/opt/Linux-x86_64/gcc-4.6.1/lib/gcc/x86_64-unknown-linux-gnu/4.6.1/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wsuggest-attribute=pure' '-O2' '-S'
'-mtune=generic' '-march=x86-64'
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/50021] -Wsuggest-attribute=pure makes obviously-incorrect suggestion
2011-08-08 7:16 [Bug c/50021] New: -Wsuggest-attribute=pure makes obviously-incorrect suggestion eggert at gnu dot org
@ 2011-08-08 10:14 ` rguenth at gcc dot gnu.org
2011-08-08 20:49 ` hubicka at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2011-08-08 10:14 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Keywords| |diagnostic, wrong-code
Last reconfirmed| |2011.08.08 10:12:05
Component|c |tree-optimization
CC| |hubicka at gcc dot gnu.org,
| |rguenth at gcc dot gnu.org
Ever Confirmed|0 |1
--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-08-08 10:12:05 UTC ---
Confirmed. We suggest 'pure' for the head of the function which was split
by partial inlining. With -fno-partial-inlining the suggestion is gone.
Honza - we need to make sure to never suggest attributes for clones
(or heads of functions which I guess we are not representing as clone?).
The bug is really bad - and I'd rate this "diagnostic issue" as wrong-code,
as that is what we suggest.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/50021] -Wsuggest-attribute=pure makes obviously-incorrect suggestion
2011-08-08 7:16 [Bug c/50021] New: -Wsuggest-attribute=pure makes obviously-incorrect suggestion eggert at gnu dot org
2011-08-08 10:14 ` [Bug tree-optimization/50021] " rguenth at gcc dot gnu.org
@ 2011-08-08 20:49 ` hubicka at gcc dot gnu.org
2011-08-09 8:28 ` rguenther at suse dot de
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: hubicka at gcc dot gnu.org @ 2011-08-08 20:49 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
--- Comment #2 from Jan Hubicka <hubicka at gcc dot gnu.org> 2011-08-08 20:48:51 UTC ---
Yep, we need to mark partial clones and supress warnings there. Do we have way
to work out from DECL if it is a clone? (from callgraph it is bit tricky in
this case when it comes to ltrans partitioning. For sure I can stick flag there
through)
Honza
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/50021] -Wsuggest-attribute=pure makes obviously-incorrect suggestion
2011-08-08 7:16 [Bug c/50021] New: -Wsuggest-attribute=pure makes obviously-incorrect suggestion eggert at gnu dot org
2011-08-08 10:14 ` [Bug tree-optimization/50021] " rguenth at gcc dot gnu.org
2011-08-08 20:49 ` hubicka at gcc dot gnu.org
@ 2011-08-09 8:28 ` rguenther at suse dot de
2012-03-25 2:56 ` bruno at clisp dot org
2014-09-26 16:11 ` hubicka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: rguenther at suse dot de @ 2011-08-09 8:28 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> 2011-08-09 08:27:16 UTC ---
On Mon, 8 Aug 2011, hubicka at gcc dot gnu.org wrote:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
>
> --- Comment #2 from Jan Hubicka <hubicka at gcc dot gnu.org> 2011-08-08 20:48:51 UTC ---
> Yep, we need to mark partial clones and supress warnings there. Do we have way
> to work out from DECL if it is a clone? (from callgraph it is bit tricky in
> this case when it comes to ltrans partitioning. For sure I can stick flag there
> through)
I'm not sure - I probably would add a decl flag for this (might be useful
for debug info as well).
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/50021] -Wsuggest-attribute=pure makes obviously-incorrect suggestion
2011-08-08 7:16 [Bug c/50021] New: -Wsuggest-attribute=pure makes obviously-incorrect suggestion eggert at gnu dot org
` (2 preceding siblings ...)
2011-08-09 8:28 ` rguenther at suse dot de
@ 2012-03-25 2:56 ` bruno at clisp dot org
2014-09-26 16:11 ` hubicka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: bruno at clisp dot org @ 2012-03-25 2:56 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
bruno at clisp dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bruno at clisp dot org
--- Comment #4 from bruno at clisp dot org 2012-03-25 01:06:41 UTC ---
Apparently fixed in GCC 4.7.0.gcc -Wsuggest-attribute=pure -O2 -S v.i
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug tree-optimization/50021] -Wsuggest-attribute=pure makes obviously-incorrect suggestion
2011-08-08 7:16 [Bug c/50021] New: -Wsuggest-attribute=pure makes obviously-incorrect suggestion eggert at gnu dot org
` (3 preceding siblings ...)
2012-03-25 2:56 ` bruno at clisp dot org
@ 2014-09-26 16:11 ` hubicka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: hubicka at gcc dot gnu.org @ 2014-09-26 16:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50021
Jan Hubicka <hubicka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #5 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Yep, fixed in 4.7+
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2014-09-26 16:11 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2011-08-08 7:16 [Bug c/50021] New: -Wsuggest-attribute=pure makes obviously-incorrect suggestion eggert at gnu dot org
2011-08-08 10:14 ` [Bug tree-optimization/50021] " rguenth at gcc dot gnu.org
2011-08-08 20:49 ` hubicka at gcc dot gnu.org
2011-08-09 8:28 ` rguenther at suse dot de
2012-03-25 2:56 ` bruno at clisp dot org
2014-09-26 16:11 ` hubicka at gcc dot gnu.org
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