Automerge: [ProfileData] Use DenseMap::try_emplace (NFC) (#140394)

We can simplify the code with structured binding and try_emplace.
Note that try_emplace default-constructs the value if omitted.

FWIW, structured binding, a C++17 feature, wasn't available in our
codebase at the time the code was written.

Author: kazutakahirata

llvm/lib/ProfileData/InstrProfWriter.cpp

@@ -178,10 +178,7 @@ void InstrProfWriter::overlapRecord(NamedInstrProfRecord &&Other,
     return;
   }
   auto &ProfileDataMap = It->second;
-  bool NewFunc;
-  ProfilingData::iterator Where;
-  std::tie(Where, NewFunc) =
-      ProfileDataMap.insert(std::make_pair(Hash, InstrProfRecord()));
+  auto [Where, NewFunc] = ProfileDataMap.try_emplace(Hash);
   if (NewFunc) {
     Overlap.addOneMismatch(FuncLevelOverlap.Test);
     return;
@@ -200,10 +197,7 @@ void InstrProfWriter::addRecord(StringRef Name, uint64_t Hash,
                                 function_ref<void(Error)> Warn) {
   auto &ProfileDataMap = FunctionData[Name];
 
-  bool NewFunc;
-  ProfilingData::iterator Where;
-  std::tie(Where, NewFunc) =
-      ProfileDataMap.insert(std::make_pair(Hash, InstrProfRecord()));
+  auto [Where, NewFunc] = ProfileDataMap.try_emplace(Hash);
   InstrProfRecord &Dest = Where->second;
 
   auto MapWarn = [&](instrprof_error E) {