On Tue, May 5, 2020 at 8:33 AM Arnd Bergmann <a...@arndb.de> wrote: > > On Tue, May 5, 2020 at 4:08 PM Andy Shevchenko > <andy.shevche...@gmail.com> wrote: > > On Tue, May 5, 2020 at 4:58 PM Arnd Bergmann <a...@arndb.de> wrote: > > > Clang normally does not warn about certain issues in inline functions when > > > it only happens in an eliminated code path. However if something else > > > goes wrong, it does tend to complain about the definition of > > > hweight_long() > > > on 32-bit targets: > > > > Shouldn't it be fixed in CLang? > > > > > include/linux/bitops.h:75:41: error: shift count >= width of type > > > [-Werror,-Wshift-count-overflow] > > > return sizeof(w) == 4 ? hweight32(w) : hweight64(w); > > > ^~~~~~~~~~~~ > > > > sizeof(w) is compile-time constant. It can easily drop the second part > > without even looking at it. > > > > > Adding an explicit cast to __u64 avoids that warning and makes it easier > > > to read other output. > > > > Looks like papering over the real issue. > > I'm not sure if there is anything to be done about it in clang, since it > always does syntactic analysis before dead-code elimination by design.
That's pretty much it. We had a patch to Clang to use delayed diagnostics to delay emitting the warning in case the AST node was dropped, but it wasn't accepted in code review. > > It is a bit odd though that it only prints the warning sometimes, but Sometimes? > I suspect this is also something that works as designed. Maybe someone > on the clang-built-linux list knows more about the background. -- Thanks, ~Nick Desaulniers
