https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96369
Bug ID: 96369
Summary: Wrong evaluation order of || operator
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: frank_yzg at outlook dot com
Target Milestone: ---
The following code snippet:
#include <stdio.h>
int main(void)
{
const long ONE = 1L;
long y = 0L;
long x = ((long) (ONE || (y = 1L)) % 8L);
printf("x = %ld, y = %ld\n", x, y); // with -O1/-O2/-O3 flag, gcc prints
x = 1, y = 1 where clang prints x = 1, y = 0
}
> $ /usr/gcc-trunk/bin/gcc -O2 -Wall -Wextra bug.c -o a.out
> $ ./a.out
> x = 1, y = 1
If the first operand of a logical-OR operation has a nonzero value, the second
operand is not evaluated. Therefore (y = 1L) should not be evaluated. It should
print y = 0 instead of y = 1.
This bug appears in GCC-4.8, GCC-6.4.0, GCC-7.5.0, GCC-8.4.0, GCC-9.3.0,
GCC-10.2.0 and GCC-11.0.0 20200501.
