diff --git a/lib/CodeGen/CGRTTI.cpp b/lib/CodeGen/CGRTTI.cpp
index d1b370a..b5cdd7f 100644
--- a/lib/CodeGen/CGRTTI.cpp
+++ b/lib/CodeGen/CGRTTI.cpp
@@ -779,28 +779,24 @@
     cast<CXXRecordDecl>(Base->getType()->getAs<RecordType>()->getDecl());
   
   if (Base->isVirtual()) {
-    if (Bases.VirtualBases.count(BaseDecl)) {
+    // Mark the virtual base as seen.
+    if (!Bases.VirtualBases.insert(BaseDecl)) {
       // If this virtual base has been seen before, then the class is diamond
       // shaped.
       Flags |= RTTIBuilder::VMI_DiamondShaped;
     } else {
       if (Bases.NonVirtualBases.count(BaseDecl))
         Flags |= RTTIBuilder::VMI_NonDiamondRepeat;
-
-      // Mark the virtual base as seen.
-      Bases.VirtualBases.insert(BaseDecl);
     }
   } else {
-    if (Bases.NonVirtualBases.count(BaseDecl)) {
+    // Mark the non-virtual base as seen.
+    if (!Bases.NonVirtualBases.insert(BaseDecl)) {
       // If this non-virtual base has been seen before, then the class has non-
       // diamond shaped repeated inheritance.
       Flags |= RTTIBuilder::VMI_NonDiamondRepeat;
     } else {
       if (Bases.VirtualBases.count(BaseDecl))
         Flags |= RTTIBuilder::VMI_NonDiamondRepeat;
-        
-      // Mark the non-virtual base as seen.
-      Bases.NonVirtualBases.insert(BaseDecl);
     }
   }
 
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 840a18e..72e3e5c 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -1051,12 +1051,10 @@
   // Lookup the entry, lazily creating it if necessary.
   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
   if (Entry) {
-    if (WeakRefReferences.count(Entry)) {
+    if (WeakRefReferences.erase(Entry)) {
       const FunctionDecl *FD = cast_or_null<FunctionDecl>(D.getDecl());
       if (FD && !FD->hasAttr<WeakAttr>())
         Entry->setLinkage(llvm::Function::ExternalLinkage);
-
-      WeakRefReferences.erase(Entry);
     }
 
     if (Entry->getType()->getElementType() == Ty)
@@ -1197,11 +1195,9 @@
   // Lookup the entry, lazily creating it if necessary.
   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
   if (Entry) {
-    if (WeakRefReferences.count(Entry)) {
+    if (WeakRefReferences.erase(Entry)) {
       if (D && !D->hasAttr<WeakAttr>())
         Entry->setLinkage(llvm::Function::ExternalLinkage);
-
-      WeakRefReferences.erase(Entry);
     }
 
     if (UnnamedAddr)
diff --git a/lib/Sema/SemaObjCProperty.cpp b/lib/Sema/SemaObjCProperty.cpp
index e465cd6..84b6096 100644
--- a/lib/Sema/SemaObjCProperty.cpp
+++ b/lib/Sema/SemaObjCProperty.cpp
@@ -1491,8 +1491,8 @@
     for (ObjCProtocolDecl::prop_iterator P = PDecl->prop_begin(),
          E = PDecl->prop_end(); P != E; ++P) {
       ObjCPropertyDecl *Prop = *P;
-      if (!PropMap.count(Prop->getIdentifier()))
-        PropMap[Prop->getIdentifier()] = Prop;
+      // Insert into PropMap if not there already.
+      PropMap.insert(std::make_pair(Prop->getIdentifier(), Prop));
     }
     // scan through protocol's protocols.
     for (ObjCProtocolDecl::protocol_iterator PI = PDecl->protocol_begin(),
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 3adbc57..ff46bf0 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -2631,7 +2631,7 @@
     
     for (unsigned I = 0, N = Mod->Imports.size(); I != N; ++I) {
       Module *Imported = Mod->Imports[I];
-      if (Visited.count(Imported))
+      if (!Visited.insert(Imported))
         continue;
       
       bool Acceptable = UnrestrictedWildcard;
@@ -2649,7 +2649,6 @@
       if (!Acceptable)
         continue;
       
-      Visited.insert(Imported);
       Stack.push_back(Imported);
     }
   }
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index cb21f82..1014658 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -2207,10 +2207,8 @@
       if (!D)
         return;
       
-      if (Deserialized.count(D)) {
-        Deserialized.erase(D);
+      if (Deserialized.erase(D))
         Chain.push_back(D);
-      }
     }
     
     void searchForID(ModuleFile &M, GlobalDeclID GlobalID) {
@@ -2331,9 +2329,8 @@
     
     void add(ObjCCategoryDecl *Cat) {
       // Only process each category once.
-      if (!Deserialized.count(Cat))
+      if (!Deserialized.erase(Cat))
         return;
-      Deserialized.erase(Cat);
       
       // Check for duplicate categories.
       if (Cat->getDeclName()) {