https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98880
Bug ID: 98880
Summary: [10/11 Regression] assignment unexpectedly optimized
away with -O
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at jochen dot sprickerhof.de
Target Milestone: ---
The following code:
#include <assert.h>
#include <unistd.h>
struct sh_lq {
ssize_t slh_first;
};
struct sh_le {
ssize_t sle_next;
};
static void sh_l_discard(struct sh_lq *list) {
struct sh_le *ele;
ele = (struct sh_le *)((char *)list + list->slh_first);
assert(ele->sle_next == -1);
}
int main() {
struct sh_lq list;
struct sh_le ele;
ele.sle_next = -1;
list.slh_first = (ssize_t)((char *)&ele - (char *)&list);
sh_l_discard(&list);
return 0;
}
compiled with gcc-10 -O fails on the assert(). It works fine with gcc-9 -O and
with gcc-10 without -O.
Tested with gcc -v:
Using built-in specs.
COLLECT_GCC=/usr/bin/gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 10.2.1-6'
--with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-10
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-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-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --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-10-Km9U7s/gcc-10-10.2.1/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-10-Km9U7s/gcc-10-10.2.1/debian/tmp-gcn/usr,hsa
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-mutex
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.1 20210110 (Debian 10.2.1-6)
Also tried with godbot: https://godbolt.org/z/xrKPj8 (without the static to
make the problem more visible)
This is extracted from:
https://sources.debian.org/src/db5.3/5.3.28+dfsg1-0.6/src/dbinc/shqueue.h/
