On Tue, 14 Jun 2022, 12:44 Jakub Jelinek, <ja...@redhat.com> wrote: > On Mon, Jun 13, 2022 at 03:53:13PM -0400, Jason Merrill via Gcc-patches > wrote: > > When not optimizing, we can't do anything useful with unreachability in > > terms of code performance, so we might as well improve debugging by > turning > > __builtin_unreachable into a trap. In the PR richi suggested > introducing an > > -funreachable-traps flag for this, but this functionality is already > > implemented as -fsanitize=unreachable > -fsanitize-undefined-trap-on-error, we > > just need to set those flags by default. > > > > I think it also makes sense to do this when we're explicitly optimizing > for > > the debugging experience. > > > > I then needed to make options-save handle -fsanitize and > > -fsanitize-undefined-trap-on-error; since -fsanitize is has custom > parsing, > > that meant handling it explicitly in the awk scripts. I also noticed we > > weren't setting it in opts_set. > > > > Do we still want -funreachable-traps as an alias (or separate flag) for > this > > behavior that doesn't mention the sanitizer? > > I do not like doing it this way, -fsanitize-undefined-trap-on-error is > (unfortunately for compatibility with llvm misdesign, users should have > ways to control which of the enabled sanitizers should be handled which > way, > where the 3 ways are runtime diagnostics without abort, runtime diagnostics > with abort and __builtin_trap ()) an all or nothing option which affects > all > the sanitizers.
It looks like clang has addressed this deficiency now: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#usage You can choose a different outcome for different checks. They also have a smaller, intended-for-production runtime now: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#minimal-runtime
