diff --git a/llvm/include/llvm/IR/ModuleSummaryIndexYAML.h b/llvm/include/llvm/IR/ModuleSummaryIndexYAML.h
index 3381e1777217a..ccb77e75492af 100644
--- a/llvm/include/llvm/IR/ModuleSummaryIndexYAML.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndexYAML.h
@@ -79,7 +79,7 @@ struct CustomMappingTraits<
       }
       Args.push_back(Arg);
     }
-    io.mapRequired(Key.str().c_str(), V[Args]);
+    io.mapRequired(Key, V[Args]);
   }
   static void output(
       IO &io,
@@ -91,7 +91,7 @@ struct CustomMappingTraits<
           Key += ',';
         Key += llvm::utostr(Arg);
       }
-      io.mapRequired(Key.c_str(), P.second);
+      io.mapRequired(Key, P.second);
     }
   }
 };
@@ -122,11 +122,11 @@ struct CustomMappingTraits<std::map<uint64_t, WholeProgramDevirtResolution>> {
       io.setError("key not an integer");
       return;
     }
-    io.mapRequired(Key.str().c_str(), V[KeyInt]);
+    io.mapRequired(Key, V[KeyInt]);
   }
   static void output(IO &io, std::map<uint64_t, WholeProgramDevirtResolution> &V) {
     for (auto &P : V)
-      io.mapRequired(llvm::utostr(P.first).c_str(), P.second);
+      io.mapRequired(llvm::utostr(P.first), P.second);
   }
 };
 
@@ -215,7 +215,7 @@ namespace yaml {
 template <> struct CustomMappingTraits<GlobalValueSummaryMapTy> {
   static void inputOne(IO &io, StringRef Key, GlobalValueSummaryMapTy &V) {
     std::vector<GlobalValueSummaryYaml> GVSums;
-    io.mapRequired(Key.str().c_str(), GVSums);
+    io.mapRequired(Key, GVSums);
     uint64_t KeyInt;
     if (Key.getAsInteger(0, KeyInt)) {
       io.setError("key not an integer");
@@ -290,7 +290,7 @@ template <> struct CustomMappingTraits<GlobalValueSummaryMapTy> {
         }
       }
       if (!GVSums.empty())
-        io.mapRequired(llvm::utostr(P.first).c_str(), GVSums);
+        io.mapRequired(llvm::utostr(P.first), GVSums);
     }
   }
   static void fixAliaseeLinks(GlobalValueSummaryMapTy &V) {
@@ -313,12 +313,12 @@ template <> struct CustomMappingTraits<GlobalValueSummaryMapTy> {
 template <> struct CustomMappingTraits<TypeIdSummaryMapTy> {
   static void inputOne(IO &io, StringRef Key, TypeIdSummaryMapTy &V) {
     TypeIdSummary TId;
-    io.mapRequired(Key.str().c_str(), TId);
+    io.mapRequired(Key, TId);
     V.insert({GlobalValue::getGUIDAssumingExternalLinkage(Key), {Key, TId}});
   }
   static void output(IO &io, TypeIdSummaryMapTy &V) {
     for (auto &TidIter : V)
-      io.mapRequired(TidIter.second.first.str().c_str(), TidIter.second.second);
+      io.mapRequired(TidIter.second.first, TidIter.second.second);
   }
 };
 
diff --git a/llvm/include/llvm/ProfileData/MemProfYAML.h b/llvm/include/llvm/ProfileData/MemProfYAML.h
index d66e16dda51d6..c55f7806d73a6 100644
--- a/llvm/include/llvm/ProfileData/MemProfYAML.h
+++ b/llvm/include/llvm/ProfileData/MemProfYAML.h
@@ -141,7 +141,7 @@ template <> struct CustomMappingTraits<memprof::PortableMemInfoBlock> {
 #define MIBEntryDef(NameTag, Name, Type)                                       \
   if (KeyStr == #Name) {                                                       \
     uint64_t Value;                                                            \
-    Io.mapRequired(KeyStr.str().c_str(), Value);                               \
+    Io.mapRequired(KeyStr, Value);                                             \
     MIB.Name = static_cast<Type>(Value);                                       \
     MIB.Schema.set(llvm::to_underlying(memprof::Meta::Name));                  \
     return;                                                                    \
diff --git a/llvm/include/llvm/Support/YAMLTraits.h b/llvm/include/llvm/Support/YAMLTraits.h
index 3d36f41ca1a04..b53b28dd00fd1 100644
--- a/llvm/include/llvm/Support/YAMLTraits.h
+++ b/llvm/include/llvm/Support/YAMLTraits.h
@@ -1921,12 +1921,12 @@ template <typename T> struct StdMapStringCustomMappingTraitsImpl {
   using map_type = std::map<std::string, T>;
 
   static void inputOne(IO &io, StringRef key, map_type &v) {
-    io.mapRequired(key.str().c_str(), v[std::string(key)]);
+    io.mapRequired(key, v[std::string(key)]);
   }
 
   static void output(IO &io, map_type &v) {
     for (auto &p : v)
-      io.mapRequired(p.first.c_str(), p.second);
+      io.mapRequired(p.first, p.second);
   }
 };
 
diff --git a/llvm/lib/BinaryFormat/MsgPackDocumentYAML.cpp b/llvm/lib/BinaryFormat/MsgPackDocumentYAML.cpp
index 3de3dccce0c6c..80b421d5f752e 100644
--- a/llvm/lib/BinaryFormat/MsgPackDocumentYAML.cpp
+++ b/llvm/lib/BinaryFormat/MsgPackDocumentYAML.cpp
@@ -209,12 +209,12 @@ template <> struct CustomMappingTraits<MapDocNode> {
   static void inputOne(IO &IO, StringRef Key, MapDocNode &M) {
     ScalarDocNode KeyObj = M.getDocument()->getNode();
     KeyObj.fromString(Key, "");
-    IO.mapRequired(Key.str().c_str(), M.getMap()[KeyObj]);
+    IO.mapRequired(Key, M.getMap()[KeyObj]);
   }
 
   static void output(IO &IO, MapDocNode &M) {
     for (auto I : M.getMap()) {
-      IO.mapRequired(I.first.toString().c_str(), I.second);
+      IO.mapRequired(I.first.toString(), I.second);
     }
   }
 };
diff --git a/llvm/lib/CGData/OutlinedHashTreeRecord.cpp b/llvm/lib/CGData/OutlinedHashTreeRecord.cpp
index cc760634d7fae..2b6e2f0537524 100644
--- a/llvm/lib/CGData/OutlinedHashTreeRecord.cpp
+++ b/llvm/lib/CGData/OutlinedHashTreeRecord.cpp
@@ -37,7 +37,7 @@ template <> struct MappingTraits<HashNodeStable> {
 template <> struct CustomMappingTraits<IdHashNodeStableMapTy> {
   static void inputOne(IO &io, StringRef Key, IdHashNodeStableMapTy &V) {
     HashNodeStable NodeStable;
-    io.mapRequired(Key.str().c_str(), NodeStable);
+    io.mapRequired(Key, NodeStable);
     unsigned Id;
     if (Key.getAsInteger(0, Id)) {
       io.setError("Id not an integer");
@@ -48,7 +48,7 @@ template <> struct CustomMappingTraits<IdHashNodeStableMapTy> {
 
   static void output(IO &io, IdHashNodeStableMapTy &V) {
     for (auto Iter = V.begin(); Iter != V.end(); ++Iter)
-      io.mapRequired(utostr(Iter->first).c_str(), Iter->second);
+      io.mapRequired(utostr(Iter->first), Iter->second);
   }
 };
 
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h b/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
index ff4d64693284a..ee575e3527673 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
@@ -207,8 +207,7 @@ template <> struct MappingTraits<WebAssemblyFunctionInfo> {
 template <> struct CustomMappingTraits<BBNumberMap> {
   static void inputOne(IO &YamlIO, StringRef Key,
                        BBNumberMap &SrcToUnwindDest) {
-    YamlIO.mapRequired(Key.str().c_str(),
-                       SrcToUnwindDest[std::atoi(Key.str().c_str())]);
+    YamlIO.mapRequired(Key, SrcToUnwindDest[std::atoi(Key.str().c_str())]);
   }
 
   static void output(IO &YamlIO, BBNumberMap &SrcToUnwindDest) {
diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp
index 1823a534a301a..ba14d5639898f 100644
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp
@@ -202,7 +202,7 @@ struct CustomMappingTraits<std::map<exegesis::ValidationEvent, int64_t>> {
       Io.setError("Key is not a valid validation event");
       return;
     }
-    Io.mapRequired(KeyStr.str().c_str(), VI[*Key]);
+    Io.mapRequired(KeyStr, VI[*Key]);
   }
 
   static void output(IO &Io, std::map<exegesis::ValidationEvent, int64_t> &VI) {
diff --git a/llvm/unittests/Support/YAMLIOTest.cpp b/llvm/unittests/Support/YAMLIOTest.cpp
index 283e5f829ba46..7446c07ccb9a8 100644
--- a/llvm/unittests/Support/YAMLIOTest.cpp
+++ b/llvm/unittests/Support/YAMLIOTest.cpp
@@ -3221,12 +3221,12 @@ template <> struct TaggedScalarTraits<Scalar> {
 
 template <> struct CustomMappingTraits<Map> {
   static void inputOne(IO &IO, StringRef Key, Map &M) {
-    IO.mapRequired(Key.str().c_str(), M[Key]);
+    IO.mapRequired(Key, M[Key]);
   }
 
   static void output(IO &IO, Map &M) {
     for (auto &N : M)
-      IO.mapRequired(N.getKey().str().c_str(), N.getValue());
+      IO.mapRequired(N.getKey(), N.getValue());
   }
 };