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* [Bug tree-optimization/113271] New: [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization)
@ 2024-01-08 12:08 652023330028 at smail dot nju.edu.cn
2024-01-08 12:16 ` [Bug tree-optimization/113271] " jakub at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: 652023330028 at smail dot nju.edu.cn @ 2024-01-08 12:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113271
Bug ID: 113271
Summary: [Regression] Wrong code at -O1/2/3 since GCC-9 (could
be due to wrong optimization)
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: 652023330028 at smail dot nju.edu.cn
Target Milestone: ---
Hello, we note that gcc may introduce erroneous code due to optimization:
https://godbolt.org/z/8vbn3KdqP
#include <iostream>
int a, b, c;
void func() {
a=-b;
//std::cout<<-a<<std::endl; //Line 5
c=(a)/(-2147483647-1);
}
int main(){
b= -2147483647 - 1;
func();
std::cout<<c;
}
The output of GCC-O0 is:
1
The output of GCC-O3 is:
0
If we uncomment the fifth line:
#include <iostream>
int a, b, c;
void func() {
a=-b;
std::cout<<-a<<std::endl; //Line 5
c=(a)/(-2147483647-1);
}
int main(){
b= -2147483647 - 1;
func();
std::cout<<c;
}
we get the correct output (GCC-O3):
-2147483648
1
This issue is probably due to a bad optimization of "func" by gcc -O3:
func():
mov DWORD PTR c[rip], 0
mov eax, DWORD PTR b[rip]
neg eax
mov DWORD PTR a[rip], eax
ret
Thank you very much for your time and effort! We look forward to hearing from
you.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/113271] [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization)
2024-01-08 12:08 [Bug tree-optimization/113271] New: [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization) 652023330028 at smail dot nju.edu.cn
@ 2024-01-08 12:16 ` jakub at gcc dot gnu.org
2024-01-09 6:14 ` xry111 at gcc dot gnu.org
2024-01-09 6:27 ` 652023330028 at smail dot nju.edu.cn
2 siblings, 0 replies; 4+ messages in thread
From: jakub at gcc dot gnu.org @ 2024-01-08 12:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113271
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
CC| |jakub at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Garbage in, garbage out.
This is UB, as can be seen if you compile with -fsanitize=undefined:
runtime error: negation of -2147483648 cannot be represented in type 'int';
cast to an unsigned type to negate this value to itself
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/113271] [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization)
2024-01-08 12:08 [Bug tree-optimization/113271] New: [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization) 652023330028 at smail dot nju.edu.cn
2024-01-08 12:16 ` [Bug tree-optimization/113271] " jakub at gcc dot gnu.org
@ 2024-01-09 6:14 ` xry111 at gcc dot gnu.org
2024-01-09 6:27 ` 652023330028 at smail dot nju.edu.cn
2 siblings, 0 replies; 4+ messages in thread
From: xry111 at gcc dot gnu.org @ 2024-01-09 6:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113271
Xi Ruoyao <xry111 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |xry111 at gcc dot gnu.org
--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
-fsanitize=undefined is even explicitly mentioned in the bug report guideline
at https://gcc.gnu.org/bugs/. And the red banner in the new bug page also
mentions -fwrapv.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/113271] [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization)
2024-01-08 12:08 [Bug tree-optimization/113271] New: [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization) 652023330028 at smail dot nju.edu.cn
2024-01-08 12:16 ` [Bug tree-optimization/113271] " jakub at gcc dot gnu.org
2024-01-09 6:14 ` xry111 at gcc dot gnu.org
@ 2024-01-09 6:27 ` 652023330028 at smail dot nju.edu.cn
2 siblings, 0 replies; 4+ messages in thread
From: 652023330028 at smail dot nju.edu.cn @ 2024-01-09 6:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113271
--- Comment #3 from Yi <652023330028 at smail dot nju.edu.cn> ---
(In reply to Xi Ruoyao from comment #2)
> -fsanitize=undefined is even explicitly mentioned in the bug report
> guideline at https://gcc.gnu.org/bugs/. And the red banner in the new bug
> page also mentions -fwrapv.
I'm sorry about this issue. I knew what you mentioned. I seemed a little out of
my mind when I brought up the issue.
(In reply to Jakub Jelinek from comment #1)
> This is UB, as can be seen if you compile with -fsanitize=undefined:
I'm sorry again.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2024-01-09 6:27 UTC | newest]
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2024-01-08 12:08 [Bug tree-optimization/113271] New: [Regression] Wrong code at -O1/2/3 since GCC-9 (could be due to wrong optimization) 652023330028 at smail dot nju.edu.cn
2024-01-08 12:16 ` [Bug tree-optimization/113271] " jakub at gcc dot gnu.org
2024-01-09 6:14 ` xry111 at gcc dot gnu.org
2024-01-09 6:27 ` 652023330028 at smail dot nju.edu.cn
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