New GCC 7 -Wformat-truncation suppressed by (and only by) -Og?

[Stephan Bergmann <sbergman at redhat dot com>]

At least with a recent GCC 7 trunk build ("gcc (GCC) 7.0.1 20170221 
(experimental)"), I noticed that -Wformat-truncation warnings happen to 
not be emitted if and only if -Og is given:

> $ cat test.c
> #include <stdio.h>
> int main() {
>     char buf[3];
>     snprintf(buf, sizeof buf, "%s", "foo");
>     return 0;
> }
> $ gcc -Wformat-truncation -Og ~/test.c
> $ gcc -Wformat-truncation -O ~/test.c
> test.c: In function ‘main’:
> test.c:4:34: warning: ‘snprintf’ output truncated before the last format character [-Wformat-truncation=]
>      snprintf(buf, sizeof buf, "%s", "foo");
>                                   ^
> test.c:4:5: note: ‘snprintf’ output 4 bytes into a destination of size 3
>      snprintf(buf, sizeof buf, "%s", "foo");
>      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Any other optimization level (-O1..3/s/fast) does emit the warning.  The 
documentation makes it clear that the behavior of that warning may be 
coupled to the optimization level, but this difference between -Og and 
everything else still looks somewhat odd.  Could it be by mistake?