PostgreSQL and compiler warnings

Recently, I did some work on backpatching a few commits from PostgreSQL master, and I noticed that with the current tools, the old branches create tons of compiler warnings. In PostgreSQL 8.3, the oldest currently supported branch, a make all with GCC 4.6.3 produces 231 warnings! (Also note that there are only 751 .c files, so that's a warning every three files.) We do a lot of work cleaning up any and all compiler warnings, at least those issued by the latest GCC. These kinds of noisy builds are quite troublesome to work with, because it is more difficult to check whether your changes introduced any new, more serious warnings.

Let's take a look at the current number of compiler warnings in different PostgreSQL branches with different compilers:

	gcc 4.4	gcc 4.5	gcc 4.6	gcc 4.7	clang
8.3	173	51	231	207	665
8.4	12	17	201	201	673
9.0	13	13	89	89	780
9.1	24	24	40	40	25
master	1	1	1	1	1

Obviously, GCC 4.6 introduced many new warnings. If you use the compiler that was current around the time the branch was originally released, you'll be better off. But even then, you should expect a few surprises. (8.3 would probably require gcc 4.3, but I don't have that available anymore.)

Fortunately, it looks as though GCC 4.7, which is currently in release candidate state, will spare us of new warnings. Also note that clang (version 3.0) is now as good as GCC, as far as noise is concerned.