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* [Bug other/27417] New: wrong code or aliasing violation with missed diagnostic?
@ 2006-05-04 10:47 pluto at agmk dot net
2006-05-04 11:58 ` [Bug other/27417] " rguenth at gcc dot gnu dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: pluto at agmk dot net @ 2006-05-04 10:47 UTC (permalink / raw)
To: gcc-bugs
inline float quickBinaryToFloat( unsigned const& in )
{
return reinterpret_cast< float const& >( in ) ;
}
float foo( unsigned x )
{
unsigned y = ( x * 2 ) + 1;
return quickBinaryToFloat( y );
}
[ wrong-code generated ]
$ i486-gnu-linux-g++ bin2float.cpp -Wall -O2 -c -fomit-frame-pointer -m32
00000000 <foo(unsigned int)>:
0: 83 ec 10 sub $0x10,%esp
3: d9 44 24 0c flds 0xc(%esp)
7: 83 c4 10 add $0x10,%esp
a: c3 ret
[ correct code generated ]
$ i486-gnu-linux-g++ bin2float.cpp -Wall -O2 -c -fomit-frame-pointer -m32 \
-fno-strict-aliasing
00000000 <foo(unsigned int)>:
0: 83 ec 10 sub $0x10,%esp
3: 8b 44 24 14 mov 0x14(%esp),%eax
7: 8d 44 00 01 lea 0x1(%eax,%eax,1),%eax
b: 89 44 24 0c mov %eax,0xc(%esp)
f: d9 44 24 0c flds 0xc(%esp)
13: 83 c4 10 add $0x10,%esp
16: c3 ret
--
Summary: wrong code or aliasing violation with missed diagnostic?
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: pluto at agmk dot net
GCC build triplet: i486-linux
GCC host triplet: i486-linux
GCC target triplet: i486-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27417
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug other/27417] wrong code or aliasing violation with missed diagnostic?
2006-05-04 10:47 [Bug other/27417] New: wrong code or aliasing violation with missed diagnostic? pluto at agmk dot net
@ 2006-05-04 11:58 ` rguenth at gcc dot gnu dot org
2006-05-04 12:08 ` pluto at agmk dot net
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2006-05-04 11:58 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from rguenth at gcc dot gnu dot org 2006-05-04 11:58 -------
This missed diagnostic is known, as enabling a warning here would cause too
much "false" positives. But yes, you are violating strict-aliasing rules here.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27417
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug other/27417] wrong code or aliasing violation with missed diagnostic?
2006-05-04 10:47 [Bug other/27417] New: wrong code or aliasing violation with missed diagnostic? pluto at agmk dot net
2006-05-04 11:58 ` [Bug other/27417] " rguenth at gcc dot gnu dot org
@ 2006-05-04 12:08 ` pluto at agmk dot net
2006-05-04 14:00 ` rguenth at gcc dot gnu dot org
2006-05-05 15:10 ` pluto at agmk dot net
3 siblings, 0 replies; 5+ messages in thread
From: pluto at agmk dot net @ 2006-05-04 12:08 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from pluto at agmk dot net 2006-05-04 12:08 -------
(In reply to comment #1)
> This missed diagnostic is known, as enabling a warning here would cause too
> much "false" positives.
but what about -Wstrict-aliasing=2?
it doesn't report anything, so how can i check possible
violations with accepted false-positive level?
--
pluto at agmk dot net changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27417
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug other/27417] wrong code or aliasing violation with missed diagnostic?
2006-05-04 10:47 [Bug other/27417] New: wrong code or aliasing violation with missed diagnostic? pluto at agmk dot net
2006-05-04 11:58 ` [Bug other/27417] " rguenth at gcc dot gnu dot org
2006-05-04 12:08 ` pluto at agmk dot net
@ 2006-05-04 14:00 ` rguenth at gcc dot gnu dot org
2006-05-05 15:10 ` pluto at agmk dot net
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2006-05-04 14:00 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from rguenth at gcc dot gnu dot org 2006-05-04 14:00 -------
You cannot. Though you can try extending c-common.c:strict_aliasing_warning
and
cp/typeck.c:build_reinterpret_cast_1 to warn in this case.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27417
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug other/27417] wrong code or aliasing violation with missed diagnostic?
2006-05-04 10:47 [Bug other/27417] New: wrong code or aliasing violation with missed diagnostic? pluto at agmk dot net
` (2 preceding siblings ...)
2006-05-04 14:00 ` rguenth at gcc dot gnu dot org
@ 2006-05-05 15:10 ` pluto at agmk dot net
3 siblings, 0 replies; 5+ messages in thread
From: pluto at agmk dot net @ 2006-05-05 15:10 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from pluto at agmk dot net 2006-05-05 15:10 -------
(In reply to comment #3)
> You cannot. Though you can try extending c-common.c:strict_aliasing_warning
> and
> cp/typeck.c:build_reinterpret_cast_1 to warn in this case.
sorry, but i don't know compiler internals to do this.
btw, maybe we should collect in one PR examples of undetected
aliasing violations for future work on better detection?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27417
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2006-05-05 15:10 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2006-05-04 10:47 [Bug other/27417] New: wrong code or aliasing violation with missed diagnostic? pluto at agmk dot net
2006-05-04 11:58 ` [Bug other/27417] " rguenth at gcc dot gnu dot org
2006-05-04 12:08 ` pluto at agmk dot net
2006-05-04 14:00 ` rguenth at gcc dot gnu dot org
2006-05-05 15:10 ` pluto at agmk dot net
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