[exDM69]

Exactly. The cost is not the overhead from the actual call - it's the fact that it inhibits other optimizations. The same applies to normal function calls when link time optimization is disabled.

This only becomes relevant in hot loops, but inlining can give big wins when combined with other optimizations.

[xorblurb]

I've seen some speculative inlining happening even without LTO (so obviously, in the same TU) with GCC.

[exDM69]

Absolutely. Seems like modern compilers inline everything they possibly can, regardless whether you mark your functions inline or not.