https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109820
Bug ID: 109820
Summary: False-positive in tautological-compare
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: ansuelsmth at gmail dot com
Target Milestone: ---
Created attachment 55058
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55058&action=edit
preprocessed file
Hi, while having fun with fixing some compilation warning to enforce WERROR on
kernel linux I faced this interesting false-positive warning.
The simple repro code is this
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
int main() {
uint32_t test;
if (((test >> 4) & 0x15) == 0x9)
return 1;
return 0;
}
Compiled with gcc -o test test.c -Wall -Werror
Result in warning
test.c: In function ‘main’:
test.c:10:34: error: bitwise comparison always evaluates to false
[-Werror=tautological-compare]
10 | if (((test >> 4) & 0x15) == 0x9)
| ^~
cc1: all warnings being treated as errors
Decreasing the 0x9 to something like 0x5 mute the warning.
It's either a false positive or a warning that gets not triggered in some
corner case.
I have attached the .i as asked in the guidelines. Don't know if -v is needed.
This is simple gcc installed from ubuntu devel
I also verified that this is present in gcc 13.1
