[clang] Use *Map::try_emplace (NFC) (#140477)

We can simplify the code with *Map::try_emplace where we need
default-constructed values while avoding calling constructors when
keys are already present.

Author: kazutakahirata

clang/lib/AST/DeclBase.cpp

@@ -1924,8 +1924,7 @@ DeclContext::lookupImpl(DeclarationName Name,
       Map = CreateStoredDeclsMap(getParentASTContext());
 
     // If we have a lookup result with no external decls, we are done.
-    std::pair<StoredDeclsMap::iterator, bool> R =
-        Map->insert(std::make_pair(Name, StoredDeclsList()));
+    std::pair<StoredDeclsMap::iterator, bool> R = Map->try_emplace(Name);
     if (!R.second && !R.first->second.hasExternalDecls())
       return R.first->second.getLookupResult();
 

clang/lib/Basic/Diagnostic.cpp

@@ -150,8 +150,7 @@ void DiagnosticsEngine::Reset(bool soft /*=false*/) {
 
 DiagnosticMapping &
 DiagnosticsEngine::DiagState::getOrAddMapping(diag::kind Diag) {
-  std::pair<iterator, bool> Result =
-      DiagMap.insert(std::make_pair(Diag, DiagnosticMapping()));
+  std::pair<iterator, bool> Result = DiagMap.try_emplace(Diag);
 
   // Initialize the entry if we added it.
   if (Result.second) {

clang/lib/Basic/SourceManager.cpp

@@ -1726,7 +1726,7 @@ void SourceManager::computeMacroArgsCache(MacroArgsMap &MacroArgsCache,
   assert(FID.isValid());
 
   // Initially no macro argument chunk is present.
-  MacroArgsCache.insert(std::make_pair(0, SourceLocation()));
+  MacroArgsCache.try_emplace(0);
 
   int ID = FID.ID;
   while (true) {

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -11350,7 +11350,7 @@ CGOpenMPRuntime::LastprivateConditionalRAII::LastprivateConditionalRAII(
     LastprivateConditionalData &Data =
         CGM.getOpenMPRuntime().LastprivateConditionalStack.emplace_back();
     for (const Decl *VD : NeedToAddForLPCsAsDisabled)
-      Data.DeclToUniqueName.insert(std::make_pair(VD, SmallString<16>()));
+      Data.DeclToUniqueName.try_emplace(VD);
     Data.Fn = CGF.CurFn;
     Data.Disabled = true;
   }

clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp

@@ -1020,7 +1020,7 @@ llvm::Function *CGOpenMPRuntimeGPU::emitTeamsOutlinedFunction(
         for (const auto &Pair : MappedDeclsFields) {
           assert(Pair.getFirst()->isCanonicalDecl() &&
                  "Expected canonical declaration");
-          Data.insert(std::make_pair(Pair.getFirst(), MappedVarData()));
+          Data.try_emplace(Pair.getFirst());
         }
       }
       Rt.emitGenericVarsProlog(CGF, Loc);
@@ -2025,7 +2025,7 @@ void CGOpenMPRuntimeGPU::emitFunctionProlog(CodeGenFunction &CGF,
   DeclToAddrMapTy &Data = I->getSecond().LocalVarData;
   for (const ValueDecl *VD : VarChecker.getEscapedDecls()) {
     assert(VD->isCanonicalDecl() && "Expected canonical declaration");
-    Data.insert(std::make_pair(VD, MappedVarData()));
+    Data.try_emplace(VD);
   }
   if (!NeedToDelayGlobalization) {
     emitGenericVarsProlog(CGF, D->getBeginLoc());

clang/lib/Lex/PPLexerChange.cpp

@@ -711,7 +711,7 @@ void Preprocessor::EnterSubmodule(Module *M, SourceLocation ImportLoc,
   ModMap.resolveConflicts(M, /*Complain=*/false);
 
   // If this is the first time we've entered this module, set up its state.
-  auto R = Submodules.insert(std::make_pair(M, SubmoduleState()));
+  auto R = Submodules.try_emplace(M);
   auto &State = R.first->second;
   bool FirstTime = R.second;
   if (FirstTime) {

clang/lib/Lex/Preprocessor.cpp

@@ -319,7 +319,7 @@ Preprocessor::macro_begin(bool IncludeExternalMacros) const {
 
   // Make sure we cover all macros in visible modules.
   for (const ModuleMacro &Macro : ModuleMacros)
-    CurSubmoduleState->Macros.insert(std::make_pair(Macro.II, MacroState()));
+    CurSubmoduleState->Macros.try_emplace(Macro.II);
 
   return CurSubmoduleState->Macros.begin();
 }

clang/lib/Sema/SemaDecl.cpp

@@ -20342,7 +20342,7 @@ bool Sema::IsValueInFlagEnum(const EnumDecl *ED, const llvm::APInt &Val,
   assert(ED->isClosedFlag() && "looking for value in non-flag or open enum");
   assert(ED->isCompleteDefinition() && "expected enum definition");
 
-  auto R = FlagBitsCache.insert(std::make_pair(ED, llvm::APInt()));
+  auto R = FlagBitsCache.try_emplace(ED);
   llvm::APInt &FlagBits = R.first->second;
 
   if (R.second) {