On Mon, Aug 28, 2023 at 03:51:00PM -0700, Nick Desaulniers wrote: > On Mon, Aug 28, 2023 at 05:18:37PM +0000, David Laight wrote: > > From: Heiko Carstens > > > Sent: 28 August 2023 16:32 > > > if (strlen(uid.vduit) > 0) > > > > Does the compiler know enough to optimise that brain-dead test? > > > > For the purposes of skipping diagnostics, no; clang performs semantic > analysis BEFORE optimization (which is handled by LLVM). As such, clang > will produce diagnostics on dead code. > > Partly because LLVM isn't very ergonomic at emitting diagnostics from > the backend, partly because Clang code owner and developers don't want > clang to emit diagnostics dependent on optimization level. > > I disagree with my compatriots, and you can read more thoughts here: > https://discourse.llvm.org/t/rfc-improving-clangs-middle-and-back-end-diagnostics/69261?u=nickdesaulniers Maybe I misunderstand what you write above, however clang (latest+greatest) does indeed optimize the strlen() away and generates code which only tests if uid.vduit[0] is zero or not. Unlike gcc, which does not optimize this away and which uses the strlen() inline assembly provided via string.h...
