Re: Debug optimized code

On Mon, 22 Sep 2008 04:43:42 +0100, Stephen Horne
<sh006d3592@blueyonder.co.uk> wrote:


>On Sat, 20 Sep 2008 04:28:36 -0400, George Neuner
><gneuner2@comcast.net> wrote:
>
>>And please don't debug code at one level and then crank up the
>>optimization for a production compile. Your ship code should always
>>be exactly what you've debugged.
>
>I disagree.
>
>Your ship code should always be what you've tested.
>You debug to diagnose bugs - not to detect them.


I agree with you, but you misunderstood me. I am in no way advocating
debugging over testing. My point is that a developer should never
test/debug code compiled with one set of optimizations and then ship
untested/undebugged code compiled using a different set of
optimizations. "It works, now compile it for speed and ship it." I
have seen people do this and it always backfires.




>Probably 99% of errors in new code are simple logic errors. Around
>99% of those behave identically whether the optimiser is on or off.


Depending on the language, there are common mistakes that can be
masked by debug compiles or which may only become apparent under
certain optimizations. And the reverse is also true - in certain
languages it is possible to write code that works fine optimized but
will break when unoptimized.


Not to mention that the compiler itself is more likely to have
strangely interacting bugs in its higher optimization levels.


George

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