Index: lib/CodeGen/CodeGenTBAA.cpp
===================================================================
--- lib/CodeGen/CodeGenTBAA.cpp
+++ lib/CodeGen/CodeGenTBAA.cpp
@@ -127,7 +127,8 @@
     return getBaseTypeInfo(QTy);
 
   const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
-  if (llvm::MDNode *N = MetadataCache[Ty])
+  llvm::MDNode *&N = MetadataCache[Ty];
+  if (N)
     return N;
 
   // Handle builtin types.
@@ -160,8 +161,7 @@
     // treating wchar_t, char16_t, and char32_t as distinct from their
     // "underlying types".
     default:
-      return MetadataCache[Ty] =
-        createTBAAScalarType(BTy->getName(Features), getChar());
+      return N = createTBAAScalarType(BTy->getName(Features), getChar());
     }
   }
 
@@ -169,14 +169,13 @@
   // an object through a glvalue of other than one of the following types the
   // behavior is undefined: [...] a char, unsigned char, or std::byte type."
   if (Ty->isStdByteType())
-    return MetadataCache[Ty] = getChar();
+    return N = getChar();
 
   // Handle pointers and references.
   // TODO: Implement C++'s type "similarity" and consider dis-"similar"
   // pointers distinct.
   if (Ty->isPointerType() || Ty->isReferenceType())
-    return MetadataCache[Ty] = createTBAAScalarType("any pointer",
-                                                    getChar());
+    return N = createTBAAScalarType("any pointer", getChar());
 
   // Enum types are distinct types. In C++ they have "underlying types",
   // however they aren't related for TBAA.
@@ -186,16 +185,16 @@
     // TODO: Is there a way to get a program-wide unique name for a
     // decl with local linkage or no linkage?
     if (!Features.CPlusPlus || !ETy->getDecl()->isExternallyVisible())
-      return MetadataCache[Ty] = getChar();
+      return N = getChar();
 
     SmallString<256> OutName;
     llvm::raw_svector_ostream Out(OutName);
     MContext.mangleTypeName(QualType(ETy, 0), Out);
-    return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
+    return N = createTBAAScalarType(OutName, getChar());
   }
 
   // For now, handle any other kind of type conservatively.
-  return MetadataCache[Ty] = getChar();
+  return N = getChar();
 }
 
 TBAAAccessInfo CodeGenTBAA::getVTablePtrAccessInfo() {
@@ -244,11 +243,10 @@
   return true;
 }
 
-llvm::MDNode *
-CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
+llvm::MDNode *CodeGenTBAA::getTBAAStructInfo(QualType QTy) {
   const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
-
-  if (llvm::MDNode *N = StructMetadataCache[Ty])
+  llvm::MDNode *&N = StructMetadataCache[Ty];
+  if (N)
     return N;
 
   SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields;
@@ -256,7 +254,7 @@
     return MDHelper.createTBAAStructNode(Fields);
 
   // For now, handle any other kind of type conservatively.
-  return StructMetadataCache[Ty] = nullptr;
+  return N = nullptr;
 }
 
 llvm::MDNode *CodeGenTBAA::getBaseTypeInfo(QualType QTy) {
@@ -264,7 +262,8 @@
     return nullptr;
 
   const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
-  if (llvm::MDNode *N = BaseTypeMetadataCache[Ty])
+  llvm::MDNode *&N = BaseTypeMetadataCache[Ty];
+  if (N)
     return N;
 
   if (const RecordType *TTy = QTy->getAs<RecordType>()) {
@@ -279,7 +278,7 @@
       llvm::MDNode *FieldNode = isValidBaseType(FieldQTy) ?
           getBaseTypeInfo(FieldQTy) : getTypeInfo(FieldQTy);
       if (!FieldNode)
-        return BaseTypeMetadataCache[Ty] = nullptr;
+        return N = nullptr;
       Fields.push_back(std::make_pair(
           FieldNode, Layout.getFieldOffset(idx) / Context.getCharWidth()));
     }
@@ -293,11 +292,10 @@
       OutName = RD->getName();
     }
     // Create the struct type node with a vector of pairs (offset, type).
-    return BaseTypeMetadataCache[Ty] =
-      MDHelper.createTBAAStructTypeNode(OutName, Fields);
+    return N = MDHelper.createTBAAStructTypeNode(OutName, Fields);
   }
 
-  return BaseTypeMetadataCache[Ty] = nullptr;
+  return N = nullptr;
 }
 
 llvm::MDNode *CodeGenTBAA::getAccessTagInfo(TBAAAccessInfo Info) {