Inlined functions can give rise to bogus warnings when they contain statically
determined branches. Testcase:

static inline int f(int x) { if (1) return 17; }
int h(int z) { return f(z); }

foo$ gcc -O2 -Wall -c foo.c
foo.c: In function 'h':
foo.c:2: warning: control may reach end of non-void function 'f' being inlined

This kind of code is not uncommon, nor bad style, and makes -Werror useless.
This is a regression from gcc 3.4.0.
The same warning is given with:

static inline int f(int x, int q) { if (q) return 17; }
int h(int z) { return f(z, 1); }