https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95141
Bug ID: 95141
Summary: Incorrect integer overflow warning message for bitand
expression
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: yadongh at vt dot edu
Target Milestone: ---
C code:
#include <stdint.h>
uint64_t test(uint8_t IA1)
{
return (uint8_t)(IA1 & 158) & 1UL;
}
Command:
gcc -c test.c
Warning message:
test.c: In function ‘test’:
test.c:5:31: warning: integer overflow in expression ‘(long unsigned int)IA1 &
158 & 1’ of type ‘long unsigned int’ results in ‘0’ [-Woverflow]
return (uint8_t)(IA1 & 158) & 1UL;
~~~~~~~~~~~~~~~~~~~~~^~~~~
gcc -v output:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 8.3.0-6'
--with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-
major-version-only --program-suffix=-8 --program-prefix=x86_64-linux-gnu-
--enable-shared --enable-linker-build-id --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --libdir=/usr/lib --enab
le-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-pl
ugin --enable-default-pie --with-system-zlib --with-target-system-zlib
--enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-mult
ilib --with-tune=generic --enable-offload-targets=nvptx-none
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 8.3.0 (Debian 8.3.0-6)
Note that I find this reproducible starting from GCC 7.1 to 10.1 (on GodBolt).
Platform:
Debian 10 Linux
Problem statement:
There are a lot of explicit/implicit integer type casts here, but in no way I
think integer overflow can happen. Note that essentially we are returning zero
here as 158 & 1 is just zero.
Some other interesting observations:
(uint8_t)(IA1 & 159) & 1UL; --- No Warning
(uint8_t)(IA1 & 158U) & 1UL; --- No Warning
(uint8_t)(IA1 & 254) & 1UL; --- Warning
(uint8_t)(IA1 & 2) & 1UL; --- No Warning
