[llvm-dev] Possible soundness issue with available_externally (split from "RFC: Add guard intrinsics")

[Sanjoy Das via llvm-dev]

Just as a reality check, I wrote up a demonstration where one link
order causes a SIGFPE and another doesn't (and the program is well
defined, as far as I can tell).  All TUs are compiled with -O3.  This is also
an instance where we don't actually speculate an inline function, but only
DSE across it (after deducing readnone).

Here's the link https://github.com/sanjoy/comdat-ipo

I've tested this with my system clang:
  Apple LLVM version 7.0.2 (clang-700.1.81)
  Target: x86_64-apple-darwin15.3.0
  Thread model: posix

I didn't test with ToT, since I don't have a build lying around.

-- Sanjoy