On Sat, Feb 09, 2013 at 09:56:12AM +0100, Johan Holmquist wrote:
As a software developer, who typically inherits code to work on rather than simply writing new, I see a potential of aggressive compiler optimizations causing trouble. It goes like this:
Programmer P inherits some application/system to improve upon. Someday he spots some piece of rather badly written code. So he sets out and rewrites that piece, happy with the improvement it brings to clarity and likely also to efficiency.
The code goes into production and, disaster. The new "improved" version runs 3 times slower than the old, making it practically unusable. The new version has to be rolled back with loss of uptime and functionality and management is not happy with P.
It just so happened that the old code triggered some aggressive optimization unbeknownst to everyone, **including the original developer**, while the new code did not. (This optimization maybe even was triggered only on a certain version of the compiler, the one that happened to be in use at the time.)
I fear being P some day.
Maybe this is something that would never happen in practice, but how to be sure...
An interesting point, but I think here "P" is still at fault. If we're talking about important software, there will be regression tests, both in terms of quality and performance? Surely there will be a canary period, parallel running of the old and new system, etc.? regards, iustin