On Wed, 7 Dec 2016, Richard Biener wrote: > >Agreed, that's what I've been using in the past for glibc test cases. > > > >If that doesn't work, we'll need something else. Separate compilation > >of test cases just to thwart compiler optimizations is a significant > >burden, and will stop working once we have LTO anyway. > > > >What about making the function definitions weak? Would that be more > >reliable? > > Adding attribute((used)) should do the trick. It introduces unknown callers > and thus without cloning disables IPA.
Hm, depending on the case I think this may be not enough: it thwarts IPA on the callee side, but still allows the compiler to optimize the caller: for example, deduce that callee is pure/const (in which case optimizations in the caller may cause it to be called fewer times than intended or never at all), apply IPA-RA, or (perhaps in future) deduce that the callee always returns non-NULL and optimize the caller accordingly. I think attribute-weak works to suppress IPA on the caller side, but that is not a good solution because it also has an effect on linking semantics, may be not available on non-ELF platforms, etc. Alexander
