1 files changed, 12 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/MemorySSAUpdater.cpp b/llvm/lib/Analysis/MemorySSAUpdater.cpp
index ce74c708df1..f2d56b05d96 100644
--- a/llvm/lib/Analysis/MemorySSAUpdater.cpp
+++ b/llvm/lib/Analysis/MemorySSAUpdater.cpp
@@ -44,15 +44,15 @@ MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(
   // First, do a cache lookup. Without this cache, certain CFG structures
   // (like a series of if statements) take exponential time to visit.
   auto Cached = CachedPreviousDef.find(BB);
-  if (Cached != CachedPreviousDef.end()) {
+  if (Cached != CachedPreviousDef.end())
     return Cached->second;
-  }
 
   // If this method is called from an unreachable block, return LoE.
   if (!MSSA->DT->isReachableFromEntry(BB))
     return MSSA->getLiveOnEntryDef();
 
-  if (BasicBlock *Pred = BB->getSinglePredecessor()) {
+  if (BasicBlock *Pred = BB->getUniquePredecessor()) {
+    VisitedBlocks.insert(BB);
     // Single predecessor case, just recurse, we can only have one definition.
     MemoryAccess *Result = getPreviousDefFromEnd(Pred, CachedPreviousDef);
     CachedPreviousDef.insert({BB, Result});
@@ -96,9 +96,15 @@ MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(
     // See if we can avoid the phi by simplifying it.
     auto *Result = tryRemoveTrivialPhi(Phi, PhiOps);
     // If we couldn't simplify, we may have to create a phi
-    if (Result == Phi && UniqueIncomingAccess && SingleAccess)
+    if (Result == Phi && UniqueIncomingAccess && SingleAccess) {
+      // A concrete Phi only exists if we created an empty one to break a cycle.
+      if (Phi) {
+        assert(Phi->operands().empty() && "Expected empty Phi");
+        Phi->replaceAllUsesWith(SingleAccess);
+        removeMemoryAccess(Phi);
+      }
       Result = SingleAccess;
-    else if (Result == Phi && !(UniqueIncomingAccess && SingleAccess)) {
+    } else if (Result == Phi && !(UniqueIncomingAccess && SingleAccess)) {
       if (!Phi)
         Phi = MSSA->createMemoryPhi(BB);
 
@@ -237,6 +243,7 @@ MemoryAccess *MemorySSAUpdater::tryRemoveTrivialPhi(MemoryPhi *Phi,
 void MemorySSAUpdater::insertUse(MemoryUse *MU, bool RenameUses) {
   InsertedPHIs.clear();
   MU->setDefiningAccess(getPreviousDef(MU));
+
   // In cases without unreachable blocks, because uses do not create new
   // may-defs, there are only two cases:
   // 1. There was a def already below us, and therefore, we should not have