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

[Eli Friedman via llvm-commits]

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@@ -575,6 +607,13 @@ class GVNSink {
     unsigned NumSunk = 0;
     ReversePostOrderTraversal<Function*> RPOT(&F);
     VN.setReachableBBs(BasicBlocksSet(RPOT.begin(), RPOT.end()));
+    // Populated DFSNumbers ahead of time to avoid updating dominator tree
+    // when CFG is modified. The DFSNumbers of newly created basic blocks
+    // are irrelevant because RPOT is also obtained ahead of time and only
+    // DFSNumbers of original CFG are relevant for sinkable candidates.
+    for (auto *BB : RPOT)
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efriedma-quic wrote:

At this point, do you actually need DFS numbering?  If any arbitrary numbering works, might as well just number in IR order.

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