Re: Compiler Revisions Should go Out As Well as Going Up.

[adambeneschan@gmail.com]

On Wednesday, December 11, 2013 6:16:35 AM UTC-8, Simon Wright wrote:

> But in some cases upgrading is a real problem. I'm thinking of systems
> that have gone through extensive and expensive validation exercises,
> including for example avionics flight tests or missile firings; even if
> you trust the compiler team, you'll have an uphill task to persuade the
> person who signs off (Design Authority, Chief Engineer, ...).

Yup.  I was involved in a project where the customer wanted the compiler ported from one host to another, but for the same embedded target.  One of their desires was for the compiler on the new host to generate the exact same binary code as the previous host; even if the compiler generated incorrect code, they wanted the new compiler to generate the same incorrect code so that they wouldn't need to revalidate.

Another somewhat similar issue comes up when a compiler incorrectly accepts illegal Ada code, and because of that, the customer gets their program working with illegal Ada in it.  Then they run into problems with newer versions of the compiler that have the bug fixed.  I've had to add a number of "compatibility" options to our Ada compiler to get it to accept illegal code that was incorrectly accepted by a 15-year-old version of the compiler.  (Or, sometimes, by some other vendor's compiler.)

                               -- Adam