https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71452
Bug ID: 71452
Summary: Wrong optimization of stores to _Bool via char*
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: ch3root at openwall dot com
Target Milestone: ---
Source code:
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#include <stdio.h>
int main()
{
_Bool b;
*(char *)&b = 123;
printf("%d\n", *(char *)&b);
}
----------------------------------------------------------------------
Results:
----------------------------------------------------------------------
$ gcc -std=c11 -pedantic -Wall -Wextra test.c && ./a.out
123
$ gcc -std=c11 -pedantic -Wall -Wextra -O3 test.c && ./a.out
1
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gcc version: gcc (GCC) 7.0.0 20160604 (experimental)
This is somewhat counterintuitive behavior and it's a bug according to
https://gcc.gnu.org/ml/gcc/2016-06/msg00046.html .
According to https://gcc.godbolt.org/ such optimization is observed with gcc
4.6.4 but not in gcc 4.5.3.
