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, 5 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index eb3f0350846..8ff00194b25 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -20464,7 +20464,7 @@ X86TargetLowering::lowerIdempotentRMWIntoFencedLoad(AtomicRMWInst *AI) const {
   // r1 = r2 = 0 is impossible, but becomes possible if the idempotent rmw is
   // lowered to just a load without a fence. A mfence flushes the store buffer,
   // making the optimization clearly correct.
-  // FIXME: it is required if isAtLeastRelease(Order) but it is not clear
+  // FIXME: it is required if isReleaseOrStronger(Order) but it is not clear
   // otherwise, we might be able to be more aggressive on relaxed idempotent
   // rmw. In practice, they do not look useful, so we don't try to be
   // especially clever.
@@ -20503,7 +20503,8 @@ static SDValue LowerATOMIC_FENCE(SDValue Op, const X86Subtarget &Subtarget,
 
   // The only fence that needs an instruction is a sequentially-consistent
   // cross-thread fence.
-  if (FenceOrdering == SequentiallyConsistent && FenceScope == CrossThread) {
+  if (FenceOrdering == AtomicOrdering::SequentiallyConsistent &&
+      FenceScope == CrossThread) {
     if (Subtarget.hasMFence())
       return DAG.getNode(X86ISD::MFENCE, dl, MVT::Other, Op.getOperand(0));
 
@@ -20986,7 +20987,8 @@ static SDValue LowerATOMIC_STORE(SDValue Op, SelectionDAG &DAG) {
   // FIXME: On 32-bit, store -> fist or movq would be more efficient
   //        (The only way to get a 16-byte store is cmpxchg16b)
   // FIXME: 16-byte ATOMIC_SWAP isn't actually hooked up at the moment.
-  if (cast<AtomicSDNode>(Node)->getOrdering() == SequentiallyConsistent ||
+  if (cast<AtomicSDNode>(Node)->getOrdering() ==
+          AtomicOrdering::SequentiallyConsistent ||
       !DAG.getTargetLoweringInfo().isTypeLegal(VT)) {
     SDValue Swap = DAG.getAtomic(ISD::ATOMIC_SWAP, dl,
                                  cast<AtomicSDNode>(Node)->getMemoryVT(),