Possible wrong-code bug in GCC?

[Haoxin Tu <haoxintu@gmail.com>]

Dear developers,

May I seek your confirmation to check whether the following program
triggers a true wrong-code issue in GCC? The following piece of code looks
too simple and I am not quite sure whether it's a bug or not.

Here is the test program (s.c):
```
int a = 0, b = 0;
int main() {
for (; a <= 6; a++) {
c:
b++;
if (b) {
goto c;
}
}
return 0;
}

```
$ gcc-trunk  -O1 s.c ; ./a.out
(infinite loop)
$ gcc-trunk -O2 s.c ;./a.out

Godbolt: https://godbolt.org/z/dx6efvv7x

I guess the behavior of -O2 is normal as the if statement inside the
for-loop will be 0 after certain iterations. It's worth noting that almost
all versions of GCC behave the same in this case. Also, note that LLVM
behaves the same under the two optimization options; they all terminate the
execution in seconds.

So, before I make any noise in the GCC bug repo, may I quickly check with
you and see whether the `s.c` is a potential wrong code bug in GCC, or
did I miss any important information here? I will file a new bug report
for this issue if it is a true bug.

Thank you so much and looking forward to your reply!


Best regards,
Haoxin