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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
Jeremy Cole
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