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, 6 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Utils/GlobalStatus.cpp b/llvm/lib/Transforms/Utils/GlobalStatus.cpp
index 3893a752503..8be42aed972 100644
--- a/llvm/lib/Transforms/Utils/GlobalStatus.cpp
+++ b/llvm/lib/Transforms/Utils/GlobalStatus.cpp
@@ -20,11 +20,11 @@ using namespace llvm;
 /// and release, then return AcquireRelease.
 ///
 static AtomicOrdering strongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
-  if (X == Acquire && Y == Release)
-    return AcquireRelease;
-  if (Y == Acquire && X == Release)
-    return AcquireRelease;
-  return (AtomicOrdering)std::max(X, Y);
+  if (X == AtomicOrdering::Acquire && Y == AtomicOrdering::Release)
+    return AtomicOrdering::AcquireRelease;
+  if (Y == AtomicOrdering::Acquire && X == AtomicOrdering::Release)
+    return AtomicOrdering::AcquireRelease;
+  return (AtomicOrdering)std::max((unsigned)X, (unsigned)Y);
 }
 
 /// It is safe to destroy a constant iff it is only used by constants itself.
@@ -185,4 +185,4 @@ GlobalStatus::GlobalStatus()
     : IsCompared(false), IsLoaded(false), StoredType(NotStored),
       StoredOnceValue(nullptr), AccessingFunction(nullptr),
       HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
-      Ordering(NotAtomic) {}
+      Ordering(AtomicOrdering::NotAtomic) {}