<div dir="ltr">On Sat, Feb 9, 2013 at 3:56 AM, Johan Holmquist <span dir="ltr"><<a href="mailto:holmisen@gmail.com" target="_blank">holmisen@gmail.com</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
The code goes into production and, disaster. The new "improved"<br>
version runs 3 times slower than the old, making it practically<br>
unusable. The new version has to be rolled back with loss of uptime<br>
and functionality and  management is not happy with P.<br>
<br>
It just so happened that the old code triggered some aggressive<br>
optimization unbeknownst to everyone, **including the original<br>
developer**, while the new code did not. (This optimization maybe even<br></blockquote><div><br></div><div>This leads ultimately to not allowing compilers to optimize at all. Â I suspect that's a bad plan. Â Keep in mind that a modern web application may be heavily enough used that it doesn't even need to be a "hyper-optimization"; even small changes in performance can scale to large performance differences.</div>
<div><br></div><div>Also... what happens when it's not just manual optimization but a bug fix that triggers this?</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Maybe this is something that would never happen in practice, but how<br>
to be sure...<br></blockquote><div>Â </div><div>If this really scares you, disable all compiler optimization. Â Now you can be sure even at large scales where even small changes can have huge effects... and now you'd better be good at hand optimization. Â And writing code in assembly language so you can get that optimization.</div>
<div><br></div><div>This sounds like going backwards to me.</div><div><br></div></div>-- <br><div dir="ltr"><div>brandon s allbery kf8nh                sine nomine associates</div><div><a href="mailto:allbery.b@gmail.com" target="_blank">allbery.b@gmail.com</a>                  <a href="mailto:ballbery@sinenomine.net" target="_blank">ballbery@sinenomine.net</a></div>
<div>unix, openafs, kerberos, infrastructure, xmonad     <a href="http://sinenomine.net" target="_blank">http://sinenomine.net</a></div></div>
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