[clang] ea22fdd - [Clang][DebugInfo] Cease turning instruction-referencing off by default

[Jeremy Morse via cfe-commits]

On Wed, Dec 22, 2021 at 4:34 PM David Blaikie via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> Is there a way to turn this off now, if it's broken for some user/use case? I guess using an -mllvm flag, instead of an -Xclang flag?

Yup, that should be achieved by "-mllvm
-experimental-debug-variable-locations=false", there's a test for that
in llvm/test/DebugInfo/X86/instr-ref-flag.ll.

> Generally I think for a significant change like this the process would be to add it under a flag, off by default, encourage people to test it by opting in via the flag, eventually change the default for the flag (letting people know they can opt-out using the flag if they see problems & to report them to you so they can be fixed & hopefully they can stop opting out) & then remove the flag when it's stable. Reverting a patch to disable a newly-on-by-default feature is a bit heavyweight and it can be nice to have a flag to control it while it's getting more exposure/experience.

Indeed, I'd hoped this was largely achieved with
https://lists.llvm.org/pipermail/llvm-dev/2021-July/151965.html , I
guess what's missing is better communicating in how to opt out now,
alas. It's unfortunate that people bisecting back are going to find
this commit; I couldn't think of another way of rectifying things
without pushing up several reverts and the re-applies at the same time
though.

--
Thanks,
Jeremy