https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118258
Bug ID: 118258
Summary: dead code causes missed optimization at -O2
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: bouncy12578 at gmail dot com
Target Milestone: ---
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc-14
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/14/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
14-20240412-0ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-14/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=/usr
--with-gcc-major-version-only --program-suffix=-14
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-libstdcxx-backtrace --enable-gnu-unique-object --disable-vtable-verify
--enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-14-OQFzmN/gcc-14-14-20240412/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-14-OQFzmN/gcc-14-14-20240412/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver
--enable-checking=yes,extra,rtl --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.0.1 20240412 (experimental) [master r14-9935-g67e1433a94f]
(Ubuntu 14-20240412-0ubuntu1)
$ cat case.c
#include <stdint.h>
int g1, g2 = 0L;
volatile int8_t g3;
volatile int8_t *g4 = &g3;
uint8_t g5;
int8_t g6;
int main() {
if (g2) {
int8_t *l = &g3;
for (g5 = 0; g5 <= 1; g5 += 1) {
*l ^= 1;
g4 = (l = &g6, (void *)0);
for (g6 = 1; (g6 >= 0); g6 -= 1)
g1 = 0;
}
} else {
for (int i = 0; i > -23; i = (uint16_t)(i - 1)) {
g3 = (g1 == 0 ? 0 : 1 % g1);
}
}
return 0;
}
$ gcc case.c -o case -O2 && ./case
Floating point exception (core dumped)
$ gcc case.c -o case -O0 && ./case
(infinite loop, the program won't stop)
This bug can be reproduced from gcc 9 or higher(but works on trunk).
Any further modification would eliminate bug.
The program is a designed infinite loop. It would crash under -O2 optimization
for gcc 9-14, -O3(and -Ofast) for gcc 9-11.
