https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101578
Bug ID: 101578
Summary: wrong code with "-O3 -fpack-struct"
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: suochenyao at 163 dot com
Target Milestone: ---
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OS and Platform:
CentOS Linux release 7.8.2003 (Core), x86_64 GNU/Linux
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Program:
int printf(const char *, ...);
struct a {
short b;
long c;
};
union {
int d;
struct a c;
} e = {0505355};
int main() {
e.c.c = 0;
printf("%d\n", e.d);
}
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gcc version:
$ gcc -v
Using built-in specs.
COLLECT_GCC=/data/bin/gcc-dev/bin/gcc
COLLECT_LTO_WRAPPER=/data/bin/gcc-dev/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/data/bin/gcc-dev --disable-multilib
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210721 (experimental) (GCC)
git version: e4d306cf706eef83f99d510c308eda1539d05875
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Command Lines:
$ gcc -O0 a.c -o a.out0
$ gcc -O3 -fpack-struct -Wall -Wextra -fno-strict-aliasing -fwrapv a.c -o
a.outf
$ ./a.out0
166637
$ ./a.outf
35565
