A simplification on Compiler process

1. Parsing ("front end"). Breaks down the code to elementary operations, and generates debug information. The C++ front end (but not the C front end) inlines some functions that were explicitly or implicitly declared inline. Both C and C++ can mark functions for the back end as "please generate inline."

2. Code generation ("back end"). Generates code, with variable levels of optimizing. Function inlining can occur at -xO3 by request, and at -xO4 or -xO5 even if not requested.

The -g option affects primarily the front ends. The back ends disable some optimizations when -g is in effect. The -g option disables front-end inlining by the C++ compiler; the -g0 option enables front-end inlining.

Most of the remaining optimization options primarily affect the back end, and are the same for C and C++. A few options are available only in C. You need to check the documentation for the compiler version you use, because new options are added from time to time.

The -fast option is really a macro that expands to a series of options based on the details of the system running the compiler. If you run the resulting program on a different machine, results will be sub-optimal, maybe even slower than if it were not compiled with -fast.

The -xOn options select optimizations that are useful across a range of systems.