[llvm] [SelectionDAG] Fix D66309: Allow unordered atomics to have some optimizations done for them (PR #85589)

[Matt Arsenault via llvm-commits]

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@@ -27934,8 +27929,7 @@ void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain,
   SmallPtrSet<SDNode *, 16> Visited;  // Visited node set.
 
   // Get alias information for node.
-  // TODO: relax aliasing for unordered atomics (see D66309)
-  const bool IsLoad = isa<LoadSDNode>(N) && cast<LoadSDNode>(N)->isSimple();
+  const bool IsLoad = isa<LoadSDNode>(N) && cast<LoadSDNode>(N)->isUnordered();
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arsenm wrote:

loads aren't tested 

https://github.com/llvm/llvm-project/pull/85589