On Tue, Jun 18, 2019 at 04:04:20PM -0700, Nathan Chancellor wrote: > On Tue, Jun 18, 2019 at 02:14:40PM -0700, Matthias Kaehlcke wrote: > > empty_child_inc/dec() use the ternary operator for conditional > > operations. The conditions involve the post/pre in/decrement > > operator and the operation is only performed when the condition > > is *not* true. This is hard to parse for humans, use a regular > > 'if' construct instead and perform the in/decrement separately. > > > > This also fixes two warnings that are emitted about the value > > of the ternary expression being unused, when building the kernel > > with clang + "kbuild: Remove unnecessary -Wno-unused-value" > > (https://lore.kernel.org/patchwork/patch/1089869/): > > > > CC net/ipv4/fib_trie.o > > net/ipv4/fib_trie.c:351:2: error: expression result unused > > [-Werror,-Wunused-value] > > ++tn_info(n)->empty_children ? : ++tn_info(n)->full_children; > > > > As an FYI, this is also being fixed in clang: > > https://bugs.llvm.org/show_bug.cgi?id=42239 > > https://reviews.llvm.org/D63369
Great, thanks! In this case it was actually useful to get the warning, even though it didn't point out the actual bug. I think in general it would be preferable to avoid such constructs, even when they are correct. But then again, it's the reviewers/maintainers task to avoid unnecessarily cryptic code from slipping in, and this just happens to be one instance where the compiler could have helped.
