(It's interesting to me if gcc doesn't warn about that libcxx code, since the whole point of the gnuc 5.0 check there was "the compiler should check this for us now"...)

Just a few more nits, and this LGTM. Thanks again!

Should we also have a quick test-case in Sema/ verifying that we still get the warnings that Eli mentioned?

Thanks for looking into this!

Thanks for reviewing!

I don't immediately see any issues with this patch, but it's outside of my area of expertise, so I'll defer to the other reviewers :)

Thanks!

Thanks for this!

Does this have any significant impact on -fsyntax-only performance?

Addressed feedback

Thanks!

LGTM, since this is a workaround to keep things rolling while we work on a more general fix.

thanks!

Thanks!

Apologies for the latency of my updates.

Chatted with Eli offline; updated here to reflect the conclusions of that.

thanks for this!

Thanks for this!

thanks!

(Now that we have D67307, is this still needed? Happy to review if so, but this seems to be addressing primarily debuginfo-related bits)

Thanks for this!

Thanks!

Assuming the test in D66495 (in part) covers this, LGTM with an optional nit.

lgtm with a few nits. Thanks!

Thanks!

Thanks!

Thanks for this! Two nits and a question

Thanks for this!

Thanks for this!

SGTM. Thanks for the review!

Thanks! If it's easy to come up with a small regression test (like David mentioned on the bug, reverse_iteration may be a great help), please do so and commit it with this. Otherwise, LGTM as-is.

LGTM with one change -- thanks!

thanks for this!

just a few drive-by nits/comments from me. as usual, not super familiar with clang-tidy, so i won't be able to stamp this.

LGTM

Thanks for this!

Thanks!

Thanks!

Thanks!

just two stylistic nits; lgtm afterward. thanks for this!

Thanks!

ping :)

ping :)

Thanks for adding this!

Please also add a test before committing if doing so is reasonably possible. If the test is super convoluted, I'm OK with this as-is.

Fair enough; thanks again!

Will submit once gribozavr indicates that they're happy with the new test names. Thanks again for working on this!

Thanks you both! LGTM with a test, assuming that adding the test is straightforward.

Thanks for this!

Thanks for the feedback!

Addressed feedback, modulo the constant foldable comment thread.

Address comments -- thanks!

neonfp isn't passed as a feature in the first place; there's a separate API setFPMath which is used for that. We translate it into a target feature for the sake of the backend. So I'm not sure what you're proposing.

Rebased

I'm happy to give rebasing it a shot later this week. My recollection of the prior state of this patch was that we wanted some backend work done to double-check that no illegal ops get generated by optimizations and such, since these checks are purely done in the frontend. I don't foresee myself having time in the near future to make that happen, so is that something that we want to continue to block this patch on? If so, then someone else is probably going to need to do that piece. Otherwise, I think people were happy enough with this patch as-is?

Thanks for this!

just letting George mark it as accepted when he's happy too

Thanks!

LGTM after two nits; thanks!

MSSA bits LGTM modulo a few nits. Feel free to commit when Chandler is happy.

I don't mean to interrupt the ongoing discussion; just wanted to send a few nits about the MSSA-specific bits. Thanks!

This sounds like people are fine with me doing this...

I can't find any users of this flag, so I'm in favor of s/EnableEarlyCSEMemSSA/true/ if that simplifies things.

Thanks!

LGTM after a nit is addressed. Thanks!

LGTM modulo one nit; thanks again!

Thanks again!

Thanks for this!

Only a few more nits on my side, and this LGTM. WDYT, arichardson?

(Forgot to refresh before pressing 'Submit', so maybe efriedma's comment answers all of the questions in mine ;) )

We have warnings like -Wdivision-by-zero that take reachability into account: https://godbolt.org/z/3PD-eF. I don't immediately know how it's all done (e.g. in batch because CFG construction is expensive? ...), but looking there for inspiration may be useful.

Thanks for this!

Thanks for this!