diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 3e1adaf84f6f..30de50dc3c88 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -14,6 +14,7 @@
 
 #include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
@@ -814,7 +815,7 @@ AliasResult BasicAAResult::alias(const MemoryLocation &LocA,
   AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags, LocB.Ptr,
                                  LocB.Size, LocB.AATags, AAQI);
 
-  VisitedPhiBBs.clear();
+  assert(VisitedPhiBBs.empty());
   return Alias;
 }
 
@@ -1654,7 +1655,11 @@ AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
   // In the recursive alias queries below, we may compare values from two
   // different loop iterations. Keep track of visited phi blocks, which will
   // be used when determining value equivalence.
-  VisitedPhiBBs.insert(PN->getParent());
+  auto Pair = VisitedPhiBBs.insert(PN->getParent());
+  auto _ = make_scope_exit([&]() {
+    if (Pair.second)
+      VisitedPhiBBs.erase(PN->getParent());
+  });
 
   AliasResult Alias = aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0], PNSize,
                                  PNAAInfo, AAQI, UnderV2);
diff --git a/llvm/test/Analysis/BasicAA/phi-aa.ll b/llvm/test/Analysis/BasicAA/phi-aa.ll
index 299dc01e7e90..aa2e078000a7 100644
--- a/llvm/test/Analysis/BasicAA/phi-aa.ll
+++ b/llvm/test/Analysis/BasicAA/phi-aa.ll
@@ -116,7 +116,7 @@ end:
 }
 
 ; CHECK-LABEL: phi_and_select
-; CHECK: MayAlias: i32* %p, i32* %s
+; CHECK: MustAlias: i32* %p, i32* %s
 define void @phi_and_select(i1 %c, i1 %c2, i32* %x, i32* %y) {
 entry:
   br i1 %c, label %true, label %false