OK, your program works. You've tested everything in sight. It's time to ship it. So you make a release version. 

And the world crumbles to dust.

You get memory access failures, dialogs don't come up, controls don't work, results come out incorrectly, or any or all of the above. Plus a few more problems that are specific to your application.

Now what?

That's what this essay is all about.

Some background

A bit of background: I have been working with optimizing compiler since 1969. My PhD dissertation (1975) was on the automatic generation of sophisticated optimizations for an optimizing compiler. My post-doctoral work involved the use of a highly optimizing compiler (Bliss-11) in the construction of a large (500K line source) operating system for a multiprocessor. After that, I was one of the architects of the PQCC (Production Quality Compiler-Compiler) effort at CMU, which was a research project to simplify the creation of sophisticated optimizing compilers. In 1981 I left the University to join Tartan Laboratories, a company that developed highly-optimizing compilers, where I was one of the major participants in the tooling development for the compilers. I've lived with, worked with, built, debugged, and survived optimizing compilers for over 30 years.

Compiler bugs

The usual first response is "the optimizer has bugs". While this can be true, it is actually a cause-of-last-resort. It is more likely that there is something else wrong with your program. We'll come back to the "compiler bugs" question a bit later. But the first assumption is that the compiler is correct, and you have a different problem. So we'll discuss those problems first.