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.
