https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116690
Bug ID: 116690
Summary: Miscompile with different optimization flags
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: yunboni at smail dot nju.edu.cn
Target Milestone: ---
Created attachment 59101
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59101&action=edit
The preprocessed file when using -O2
When I compiled this code with -O0 and -O2 flags, its outputs were different:
```c
#include <stdint.h>
#include <stdio.h>
int32_t b = 2392213176;
uint32_t e(uint32_t, uint32_t f) { return -f; }
long a(int, int, int) {}
int16_t c(int64_t);
uint32_t d() { c(b); }
int16_t c(int64_t) {
for (b = 9; a(0, 0, 0) + b > 0; b = e(0, 3))
;
}
int main() {
d();
printf("%d\n", b);
}
```
With -O0, its output is -3, while its output is 9 with -O2.
I used gcc v11.1 to compile and this miscompile still exists. Details can be
found here: https://godbolt.org/z/hzq99xdfj
My gcc version is:
Using built-in specs.
COLLECT_GCC=/home/yunbo/eval/compilers/gcc_latest/bin/gcc
COLLECT_LTO_WRAPPER=/home/yunbo/eval/compilers/gcc_latest/libexec/gcc/x86_64-pc-linux-gnu/15.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++ --prefix=/home/yunbo/eval/compilers/gcc_latest
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.0 20240909 (experimental) (GCC)
