NFC: make AtomicOrdering an enum class

Summary:
In the context of http://wg21.link/lwg2445 C++ uses the concept of
'stronger' ordering but doesn't define it properly. This should be fixed
in C++17 barring a small question that's still open.

The code currently plays fast and loose with the AtomicOrdering
enum. Using an enum class is one step towards tightening things. I later
also want to tighten related enums, such as clang's
AtomicOrderingKind (which should be shared with LLVM as a 'C++ ABI'
enum).

This change touches a few lines of code which can be improved later, I'd
like to keep it as NFC for now as it's already quite complex. I have
related changes for clang.

As a follow-up I'll add:
  bool operator<(AtomicOrdering, AtomicOrdering) = delete;
  bool operator>(AtomicOrdering, AtomicOrdering) = delete;
  bool operator<=(AtomicOrdering, AtomicOrdering) = delete;
  bool operator>=(AtomicOrdering, AtomicOrdering) = delete;
This is separate so that clang and LLVM changes don't need to be in sync.

Reviewers: jyknight, reames

Subscribers: jyknight, llvm-commits

Differential Revision: http://reviews.llvm.org/D18775

llvm-svn: 265602

1 files changed, 8 insertions, 7 deletions

diff --git a/llvm/lib/Target/CppBackend/CPPBackend.cpp b/llvm/lib/Target/CppBackend/CPPBackend.cpp
index cfa1f2ce619..a086e710d16 100644
--- a/llvm/lib/Target/CppBackend/CPPBackend.cpp
+++ b/llvm/lib/Target/CppBackend/CPPBackend.cpp
@@ -1091,13 +1091,14 @@ std::string CppWriter::getOpName(const Value* V) {
 
 static StringRef ConvertAtomicOrdering(AtomicOrdering Ordering) {
   switch (Ordering) {
-    case NotAtomic: return "NotAtomic";
-    case Unordered: return "Unordered";
-    case Monotonic: return "Monotonic";
-    case Acquire: return "Acquire";
-    case Release: return "Release";
-    case AcquireRelease: return "AcquireRelease";
-    case SequentiallyConsistent: return "SequentiallyConsistent";
+    case AtomicOrdering::NotAtomic: return "NotAtomic";
+    case AtomicOrdering::Unordered: return "Unordered";
+    case AtomicOrdering::Monotonic: return "Monotonic";
+    case AtomicOrdering::Acquire: return "Acquire";
+    case AtomicOrdering::Release: return "Release";
+    case AtomicOrdering::AcquireRelease: return "AcquireRelease";
+    case AtomicOrdering::SequentiallyConsistent:
+      return "SequentiallyConsistent";
   }
   llvm_unreachable("Unknown ordering");
 }