[Atomics] warn about atomic accesses using libcalls

If an atomic variable is misaligned (and that suspicion is why Clang emits
libcalls at all) the runtime support library will have to use a lock to safely
access it, with potentially very bad performance consequences. There's a very
good chance this is unintentional so it makes sense to issue a warning.

Also give it a named group so people can promote it to an error, or disable it
if they really don't care.

llvm-svn: 330566
3 files changed
tree: 5a8cedadab811c489ac6d8cff61641098286319a
  1. clang/
  2. clang-tools-extra/
  3. compiler-rt/
  4. debuginfo-tests/
  5. libclc/
  6. libcxx/
  7. libcxxabi/
  8. libunwind/
  9. lld/
  10. lldb/
  11. llgo/
  12. llvm/
  13. openmp/
  14. parallel-libs/
  15. polly/
  16. README.md
README.md

Low Level Virtual Machine (LLVM)

This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.