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

[Stephan Bergmann]

On 02/23/2017 02:51 PM, Stephan Bergmann wrote:
> 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

-O0..3, even

> 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?