[WebAssembly] Support for atomic fences
Summary:
This adds support for translation of LLVM IR fence instruction. We
convert a singlethread fence to a pseudo compiler barrier which becomes
0 instructions in final binary, and a thread fence to an idempotent
atomicrmw instruction to a memory address.
Reviewers: dschuff, jfb, sunfish, tlively
Subscribers: sbc100, jgravelle-google, llvm-commits
Differential Revision: https://reviews.llvm.org/D50277
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@361884
91177308-0d34-0410-b5e6-
96231b3b80d8