Stewart,

You're right that it's entirely up to the optimizer to optimize out that variable (and in fact I hope that it would). That should not change the "unused-variable" warning though, as that static analysis done by the compiler happens much earlier, as far as I know. That is, the detection of the variable being unused should be completely independent of the optimizer's decision to eliminate the variable entirely.

Regards,

Jeremy

On Wed, Aug 7, 2013 at 2:14 AM, Stewart Smith <stewart@flamingspork.com> wrote:

Jeremy Cole <jeremycole@google.com> writes:
> The attached patch adds what amounts to compile-time checking for unmatched
> DBUG_ENTER/DBUG_LEAVE (DBUG_RETURN, DBUG_VOID_RETURN) by introducing a
> variable in DBUG_ENTER which is only used in DBUG_LEAVE. This allows any
> compiler which can robustly detect unused variables to detect the mismatch
> at compile-time. There is already a run-time check for this case, but it is
> somewhat limited as it requires _db_return_ to be called in order to detect
> the mismatch, and this is in practice not always the case. Particularly
> three cases allow this to escape detection:

Ideally we'd be able to check for gcc attribute noreturn but I'm not
sure there's a way to do that (as it's not a preproceessor thing).

I'm pretty sure that with some optimization levels that the temp
variable can get optimized out (although I haven't looked at the
produced code).

Personally, looks good and I'm tempted to pull it into Percona Server.
--
Stewart Smith