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* [Bug c++/99162] New: problem when compile with O2 or O3
@ 2021-02-19 12:19 haibin-zhang at 263 dot net
2021-02-19 13:28 ` [Bug c++/99162] " pinskia at gcc dot gnu.org
2021-02-19 14:00 ` redi at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: haibin-zhang at 263 dot net @ 2021-02-19 12:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99162
Bug ID: 99162
Summary: problem when compile with O2 or O3
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: haibin-zhang at 263 dot net
Target Milestone: ---
$ g++ --version
g++ (GCC) 4.9.2
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ cat a.C
#include <stdlib.h>
#include <stdio.h>
void f(int n) {
unsigned int u = abs(n);
while(true) {
if(u < 10) {
printf("u = %u\n", u);
break;
}
printf("u = %u\n", u);
u /= 10;
}
}
main() {
f(0x80000000);
}
//////////////////////// 02 or 03 can not work ////////////////////////
$ g++ a.C -O2
$ ./a.out
u = 2147483648
//////////////////////// O1 no problem ////////////////////////////////
$ g++ a.C -O1
$ ./a.out
u = 2147483648
u = 214748364
u = 21474836
u = 2147483
u = 214748
u = 21474
u = 2147
u = 214
u = 21
u = 2
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/99162] problem when compile with O2 or O3
2021-02-19 12:19 [Bug c++/99162] New: problem when compile with O2 or O3 haibin-zhang at 263 dot net
@ 2021-02-19 13:28 ` pinskia at gcc dot gnu.org
2021-02-19 14:00 ` redi at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-02-19 13:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99162
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Signed integer overflow is undefined behavior. Abs of most negative signed
integer is undefined because there is no way to represent the positive value so
it causes an overflow.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/99162] problem when compile with O2 or O3
2021-02-19 12:19 [Bug c++/99162] New: problem when compile with O2 or O3 haibin-zhang at 263 dot net
2021-02-19 13:28 ` [Bug c++/99162] " pinskia at gcc dot gnu.org
@ 2021-02-19 14:00 ` redi at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: redi at gcc dot gnu.org @ 2021-02-19 14:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99162
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Zhang Haibin from comment #0)
> $ g++ --version
> g++ (GCC) 4.9.2
This compiler is ancient and we're not interested in bug reports for it.
If you use a modern compiler you can use -fsanitize=undefined to find bugs like
this integer overflow problem.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-02-19 14:00 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-02-19 12:19 [Bug c++/99162] New: problem when compile with O2 or O3 haibin-zhang at 263 dot net
2021-02-19 13:28 ` [Bug c++/99162] " pinskia at gcc dot gnu.org
2021-02-19 14:00 ` redi at gcc dot gnu.org
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