[llvm] [GVNSink] Fix non-determinisms by using Depth-First ordering (PR #90995)

[Eli Friedman via llvm-commits]

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@@ -222,20 +222,29 @@ raw_ostream &operator<<(raw_ostream &OS, const SinkingInstructionCandidate &C) {
 class ModelledPHI {
   SmallVector<Value *, 4> Values;
   SmallVector<BasicBlock *, 4> Blocks;
+  DominatorTree *DT;
 
 public:
   ModelledPHI() = default;
 
-  ModelledPHI(const PHINode *PN) {
+  ModelledPHI(const PHINode *PN, DominatorTree *DT) : DT(DT) {
     // BasicBlock comes first so we sort by basic block pointer order, then by value pointer order.
-    SmallVector<std::pair<BasicBlock *, Value *>, 4> Ops;
+    using OpsType = std::pair<BasicBlock *, Value *>;
+    SmallVector<OpsType, 4> Ops;
     for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I)
       Ops.push_back({PN->getIncomingBlock(I), PN->getIncomingValue(I)});
-    llvm::sort(Ops);
+
+    auto DFSOrder = [DT](OpsType O1, OpsType O2) {
+      return DT->getNode(O1.first) < DT->getNode(O2.first);
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efriedma-quic wrote:

DT->getNode() returns a pointer.  If you want the domtree to generate DFS numbers, you need to explicitly request them (see updateDFSNumbers()/getDFSNumIn()).

Splitting an edge with SplitBlockPredecessors will invalidate this numbering; not sure how you handle that.

https://github.com/llvm/llvm-project/pull/90995