[llvm] [SimplifyCFG] Avoid increasing too many phi entries when removing empty blocks (PR #104887)

[Yingwei Zheng via llvm-commits]

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@@ -1047,6 +1053,34 @@ CanRedirectPredsOfEmptyBBToSucc(BasicBlock *BB, BasicBlock *Succ,
   return true;
 }
 
+// Check whether removing BB will make the phis in its Succ have too
+// many incoming entries. This function does not check whether BB is foldable
+// or not.
+static bool introduceTooManyPhiEntries(BasicBlock *BB, BasicBlock *Succ) {
+  // If BB only has one predecessor, then removing it will not introduce more
+  // incoming edges for phis.
+  if (BB->hasNPredecessors(1))
+    return false;
+  unsigned NumPreds = pred_size(BB);
+  unsigned NumChangedPhi = 0;
+  for (auto &Phi : Succ->phis()) {
+    // If the incoming value is a phi and the phi is defined in BB,
+    // then removing BB will not increase the total phi entries of the ir.
+    if (PHINode *IncomingPhi =
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dtcxzyw wrote:

Missing test for this case.


https://github.com/llvm/llvm-project/pull/104887