[llvm] [FuncSpec] Update function specialization to handle phi-chains (PR #71442)

[Momchil Velikov via llvm-commits]

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@@ -262,30 +267,86 @@ Cost InstCostVisitor::estimateBranchInst(BranchInst &I) {
   return estimateBasicBlocks(WorkList);
 }
 
+void InstCostVisitor::discoverStronglyConnectedComponent(PHINode *PN,
+                                                         unsigned Depth) {
+  if (Depth > MaxDiscoveryDepth)
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momchil-velikov wrote:

Even assuming the "SCC" algorithm itself works, exceeding the time/depth limit would mean that we bail - because we cannot say anything useful about PHIs that are in `StronglyConnectedPHIs` or about PHIs that are **not** in `StronglyConnectedPHIs. Yet, this case is indistinguishable from normal termination.

https://github.com/llvm/llvm-project/pull/71442