https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82437
Bug ID: 82437
Summary: false-positive -Wtautological-compare warning with
-std=gnu89
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: arnd at linaro dot org
Target Milestone: ---
I found several instances of a new warning in the linux kernel, building with
"gcc-8.0.0 -std=gnu89", reduced a test case to this:
$ arm-linux-gnueabi-gcc-8.0.0 -c vfpmodule.c -std=c89 -Wall
int f(unsigned int x)
{
if ((x & ((1 << 31) | (1 << 28))) != ((1 << 31) | (1 << 28)))
return 0;
return 1;
}
vfpmodule.c: In function 'f':
vfpmodule.c:3:36: warning: bitwise comparison always evaluates to true
[-Wtautological-compare]
if ((x & ((1 << 31) | (1 << 28))) != ((1 << 31) | (1 << 28)))
The object code that gets produces looks correct, so I assume this is simply a
warning problem, possibly related to pr81783 that introduced new warnings.
