[AsmParser] Simplify code with std::map::operator[] (NFC) (#111480)

Author: kazutakahirata

llvm/lib/AsmParser/LLParser.cpp

@@ -4000,11 +4000,7 @@ bool LLParser::parseValID(ValID &ID, PerFunctionState *PFS, Type *ExpectedTy) {
     if (!F) {
       // Make a global variable as a placeholder for this reference.
       GlobalValue *&FwdRef =
-          ForwardRefBlockAddresses.insert(std::make_pair(
-                                              std::move(Fn),
-                                              std::map<ValID, GlobalValue *>()))
-              .first->second.insert(std::make_pair(std::move(Label), nullptr))
-              .first->second;
+          ForwardRefBlockAddresses[std::move(Fn)][std::move(Label)];
       if (!FwdRef) {
         unsigned FwdDeclAS;
         if (ExpectedTy) {
@@ -4082,7 +4078,7 @@ bool LLParser::parseValID(ValID &ID, PerFunctionState *PFS, Type *ExpectedTy) {
       auto &FwdRefMap = (Fn.Kind == ValID::t_GlobalID)
                             ? ForwardRefDSOLocalEquivalentIDs
                             : ForwardRefDSOLocalEquivalentNames;
-      GlobalValue *&FwdRef = FwdRefMap.try_emplace(Fn, nullptr).first->second;
+      GlobalValue *&FwdRef = FwdRefMap[Fn];
       if (!FwdRef) {
         FwdRef = new GlobalVariable(*M, Type::getInt8Ty(Context), false,
                                     GlobalValue::InternalLinkage, nullptr, "",