> > Hello. > > Maybe a silly question, but isn't the code only an obfuscation? > What about doing: > > if (__builtin_constant_p(x)) > return x < 2 ? 0 : __builtin_clz(x); > > which is fully eliminated in a c.031t.ccp1 pass right after einline happens > for a call context where 'x' is a constant. > > Isn't the right place for fix in Linux kernel?
Yes, Linux kernel should be fixed and that is discussed in the corresponding PR (there is also correct replacement for that log1 function suggested already). However there are many additional examples of similar inline functions doing (ab)use of builtin_constant_p (and not all of them translating to an existing gcc builtin). So adding a heuristics seems useful (since it is quite reliable heuristics I would say). Also in the context of decreasing the -O2 inliner defaults in gcc10 I think number of such inliner became unlucky and are no longer inlined as expected (a problem I did not realize until looking into the PR) Honza > > Martin
