Fix a bug in the definition of isUnordered on MachineMemOperand

Background: At the moment, we record the AtomicOrdering of an access in the MMO, but also mark any atomic access as volatile in SelectionDAG. GlobalISEL keeps the two separate, but currently doesn't know how to lower an atomic G_LOAD at all. See https://reviews.llvm.org/D57601 for context.

The definition used for unordered was only checking volatility, not atomicity. As noted above, all atomic MMOs are currently also volatile, so this is a latent bug only. Copy the definition used in IR, after auditing the two (2) uses of the function to be sure the desired semantics are the same.

Differential Revision: https://reviews.llvm.org/D57593

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@352898 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/MachineMemOperand.h b/include/llvm/CodeGen/MachineMemOperand.h
index 3a80c69232a1279d83ce42ae95241fc85696d921..12fae2f5663db2a3e40d20b656acaf07b5f970a2 100644 (file)
--- a/include/llvm/CodeGen/MachineMemOperand.h
+++ b/include/llvm/CodeGen/MachineMemOperand.h
@@ -266,13 +266,13 @@ public:
   bool isAtomic() const { return getOrdering() != AtomicOrdering::NotAtomic; }
 
   /// Returns true if this memory operation doesn't have any ordering
-  /// constraints other than normal aliasing. Volatile and atomic memory
-  /// operations can't be reordered.
-  ///
-  /// Currently, we don't model the difference between volatile and atomic
-  /// operations. They should retain their ordering relative to all memory
-  /// operations.
-  bool isUnordered() const { return !isVolatile(); }
+  /// constraints other than normal aliasing. Volatile and (ordered) atomic
+  /// memory operations can't be reordered. 
+  bool isUnordered() const {
+    return (getOrdering() == AtomicOrdering::NotAtomic ||
+            getOrdering() == AtomicOrdering::Unordered) &&
+           !isVolatile();
+  }
 
   /// Update this MachineMemOperand to reflect the alignment of MMO, if it has a
   /// greater alignment. This must only be used when the new alignment applies