RFR: 8263718: unused-result warning happens at os_linux.cpp

[Thomas Stuefe]

On Thu, 18 Mar 2021 09:48:27 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>>> "Note that a logical negation prior to cast to void is sufficient to suppress the warning:
>>> 
>>> ```
>>>   int void_cast_should_not_warn() {
>>>      (void) !foo();
>>>      //     ^-- here
>>>      return 0;
>>>   }
>>> ```
>>> 
>>> "
>> 
>> The warning has gone with `(void)!`, but isn't is strange a bit? IMHO code changes or pragma (or compiler option) are suitable than it.
>
> I can't really comment on which is better -- it's up to you hotspot developers.
> 
> Nevertheless, my personal preference is that `(void)` would have been best since it's a well-established idiom. If gcc is buggy about this, then I think I'd preferred to use this workaround with a comment `// the ! is needed to workaround gcc bug`, to keep with the idiom as much as possible. Pragmas also work, but I personally consider them ugly and a last resort. But once again, don't listen to what I'm saying :-)

I agree with Magnus. BTW, we are sure that alloca() call is not simply optimized away, right? Otherwise I would assign the return value to some file static volatile holder.

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PR: https://git.openjdk.java.net/jdk/pull/3042